View source for Mauna Loa

{{short description|Volcano in Hawaii, United States}}
{{distinguish|Mauna Kea}}
{{Other uses}}
{{pp-semi-indef}}
{{pp-move-indef}}
{{Use mdy dates|date=November 2022}}
{{Infobox mountain
 | name              = Mauna Loa
 | photo             = Mauna Loa Volcano.jpg
 | photo_caption     = Mauna Loa as seen from the air.<br />[[Hualālai]] is visible in the background.
 | photo_size        = 300px
 | elevation_ft      = 13679
 | elevation_ref     = <ref name=usgs/>
 | prominence_ft     = 7079
 | prominence_ref    = <ref name="peakbagger">{{cite peakbagger|pid=11915|title=Mauna Loa, Hawaii|access-date=December 12, 2012}}</ref>
 | listing           = {{unbulleted list
 | [[List of the highest major summits of the United States|US highest major peaks]] 66th
 | [[List of the most prominent summits of the United States|US most prominent peaks]] 38th
 | [[List of the highest major summits of Hawaii|Hawaii highest major peaks]] 2nd}}
 | location          = Hawaii, U.S.
 | range             = [[Hawaiian Islands]]
 | map               = United States Hawaii (island)#USA Hawaii
 | range_coordinates = 
 | coordinates       = {{coord|19|28|46|N|155|36|10|W|type:mountain_region:US-HI_scale:100000|format=dms|display=inline,title}}
 | coordinates_ref   = 
 | topo              = [[United States Geological Survey|USGS]] Mauna Loa
 | type              = [[Shield volcano]]
 | age               = 700,000–1 million<ref name=hvo-loa />
 | volcanic_zone     = [[Hawaiian-Emperor seamount chain]]
 | last_eruption     = [[2022 eruption of Mauna Loa|November 27 – December 13, 2022]]
 | first_ascent      = Ancient times
 | easiest_route     = [[Ainapo Trail]]}}
'''Mauna Loa''' ({{IPAc-en|ˌ|m|ɔː|n|ə|_|ˈ|l|oʊ|.|ə|,_|ˌ|m|aʊ|n|ə|_|-}}, {{IPA|haw|ˈmɐwnə ˈlowə|Lang|link=yes}}; {{lit|Long Mountain}}<ref name=usgs>{{cite web
 | url          = https://www.usgs.gov/volcanoes/mauna-loa
 | title        = Mauna Loa
 | work         = [[USGS]]
 | access-date  = 2023-12-19}}</ref>) is one of [[Hawaii (island)#Volcanism|five volcanoes]] that form the [[Hawaii (island)|Island of Hawaii]] in the U.S. state of Hawaii in the [[North Pacific Ocean|Pacific Ocean]]. Mauna Loa is Earth's largest [[Volcano#Active|active]] volcano<ref name=usgs/> by both mass and volume. It was historically considered to be the largest volcano on Earth until the submarine mountain [[Tamu Massif]] was discovered to be larger.<ref name="tamu" /> Mauna Loa is a [[shield volcano]] with relatively gentle slopes, and a volume estimated at {{convert|18000|mi3|km3}},<ref>{{cite conference
 | last         = Kaye|first=G.D.
 | title        = Using GIS to estimate the total volume of Mauna Loa Volcano, Hawaii
 | url          = http://gsa.confex.com/gsa/2002CD/finalprogram/abstract_34712.htm
 | work         = 98th Annual Meeting
 | conference   = Geological Society of America
 | date         = 2002-05-14
 | access-date  = August 5, 2007
 | archive-url  = https://web.archive.org/web/20090125194545/http://gsa.confex.com/gsa/2002CD/finalprogram/abstract_34712.htm
 | archive-date = 2009-01-25
 }}</ref> although its peak is about {{convert|125|ft|m|0}} lower than that of its neighbor, [[Mauna Kea]].<ref name=maunakea>{{cite web
 | title        = Mauna Kea
 | url          = http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=TU2314
 | work         = NGS Station Datasheet
 | publisher    = [[United States National Geodetic Survey]]
 | date         = 2022-11-28}}</ref> Lava eruptions from Mauna Loa are [[silica]]-poor and very fluid, and tend to be [[Hawaiian eruption|non-explosive]].

Mauna Loa has likely been erupting for at least 700,000&nbsp;years, and may have emerged above sea level about 400,000&nbsp;years ago. Some dated rocks are 470,000&nbsp;years old.<ref name=Jicha2012>{{cite journal
 | last1         = Jicha
 | first1        = B.R.
 | last2         = Rhodes
 | first2        = J.M.
 | last3         = Singer
 | first3        = B.S. 
 | last4         = Garcia
 | first4        = M.O.
 | title         = 40Ar/39Ar geochronology of submarine Mauna Loa volcano, Hawaii
 | journal       = Journal of Geophysical Research: Solid Earth
 | year          = 2012
 | volume        = 117
 | issue         = B9
 | doi           = 10.1029/2012JB009373
 | doi-access    = free}}
</ref> The volcano's [[magma]] comes from the [[Hawaii hotspot]], which has been responsible for the creation of the [[Hawaiian Islands|Hawaiian Island chain]] over tens of millions of years. The slow [[Plate tectonics#Continental drift|drift]] of the [[Pacific Plate]] will eventually carry Mauna Loa away from the hotspot within 500,000 to one million years from now, at which point it will become extinct.

[[2022 eruption of Mauna Loa|Mauna Loa's most recent eruption]] began on November 27, 2022, and ended on December 13, 2022. It was the first eruption since [[1984 eruption of Mauna Loa|1984]].<ref name="hvo-loa-2022">{{Cite web
 | title        = HAWAIIAN VOLCANO OBSERVATORY VOLCANO OBSERVATORY NOTICE FOR AVIATION Monday, November 28, 2022, 09:45 UTC {{!}} USGS Hazard Notification System (HANS) for Volcanoes
 | url          = https://volcanoes.usgs.gov/hans2/view/notice/DOI-USGS-HVO-2022-11-28T01:28:44-08:00
 | date         = 2022-11-27
 | access-date  = 2022-11-28
 | website      = volcanoes.usgs.gov}}</ref><ref>{{Cite news |title=Hawaii's Mauna Loa volcano erupts for first time in 38 years |language=en-US |newspaper=[[The Washington Post]] |url=https://www.washingtonpost.com/nation/2022/11/28/hawaii-volcano-mauna-loa-eruption/ |access-date=2022-11-29 |issn=0190-8286}}</ref> No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of [[Hilo]] is partly built on lava flows from the late 19th century.

Because of the potential hazards it poses to population centers, Mauna Loa is part of the [[Decade Volcanoes]] program, which encourages studies of the world's most dangerous volcanoes. Mauna Loa has been monitored intensively by the [[Hawaiian Volcano Observatory]] since 1912. Observations of the atmosphere are undertaken at the [[Mauna Loa Observatory]], and of the Sun at the [[Mauna Loa Solar Observatory]], both located near the mountain's summit. [[Hawaii Volcanoes National Park]] covers the summit and portions of the southeastern and southwestern flanks of the volcano, and also incorporates [[Kīlauea]], a separate volcano.

==Geology==
===Setting===
{{multiple image | direction = horizontal | align=left| width1 = 187 | width2 = 200 |image1=Mapmaunaloa.svg|caption1=Position of Mauna Loa on [[Hawaii (island)|Hawaiʻi island]]|image2=Island of Hawai'i - Landsat mosaic.jpg|caption2=[[Landsat]] mosaic; recent lava flows appear in black}}

Like all Hawaiian volcanoes, Mauna Loa was created as the [[Pacific Plate|Pacific tectonic plate]] moved over the [[Hawaii hotspot]] in the Earth's underlying [[mantle (geology)|mantle]].<ref name=usgs-map>{{cite web|title=Geologic Map of the State of Hawaiʻi|url=https://pubs.usgs.gov/of/2007/1089/Hawaii_expl_pamphlet.pdf|work=Open-File Report 2007–1089|publisher=[[United States Geological Survey]]|access-date=December 9, 2012|pages=50–51|year=2007|author1=David R. Sherrod |author2=John M. Sinton |author3=Sarah E. Watkins |author4=Kelly M. Brunt |name-list-style=amp}}</ref> The Hawaii island volcanoes are the most recent evidence of this process that, over 70&nbsp;million years, has created the {{convert|3700|mi|km|abbr=on}}-long [[Hawaiian–Emperor seamount chain]].<ref name="Watson">{{cite web|last=Watson|first=Jim|title=The long trail of the Hawaiian hotspot|url=https://pubs.usgs.gov/gip/dynamic/Hawaiian.html|publisher=United States Geological Survey|access-date=August 26, 2010|date=May 5, 1999}}</ref> The prevailing view states that the hotspot has been largely stationary within the planet's mantle for much, if not all of the [[Cenozoic]] Era.<ref name="Watson"/><ref>{{cite web|url=http://www.mantleplumes.org/Hawaii.html|title=The Emperor and Hawaiian Volcanic Chains: How well do they fit the plume hypothesis?|author1=Foulger, G.R |author2=Anderson, Don L.
|publisher=MantlePlumes.org|date=March 11, 2006|access-date=April 1, 2009}}</ref> However, while the Hawaiian [[mantle plume]] is well understood and extensively studied, the nature of hotspots themselves remains fairly enigmatic.<ref>{{Cite book|year=1987 |title=Volcanism in Hawaii: papers to commemorate the 75th anniversary of the founding of the Hawaii Volcano Observatory |chapter=The Hawaiian-Emperor Volcanic Chain – Geological Evolution |publisher=United States Geological Survey |volume=1 |series=Professional Paper 1350 |chapter-url=https://pubs.usgs.gov/pp/1987/1350/pdf/chapters/pp1350_ch1.pdf |page=32 |author1=Clague, David A. |author2=Dalrymple, G. Brent}}</ref>

Mauna Loa is one of five [[subaerial]]{{efn|occurring on or near the&nbsp;Earth's land surface as opposed to submarine (below the sea), sub-glacial (below a glacier), etc.}} volcanoes that make up the island of [[Hawaii (island)|Hawaiʻi]].<ref>{{cite book |editor1-last=Juvik |editor1-first=Sonia P. |editor2-last=Juvik |editor2-first=James O. |title=Atlas of Hawaiʻi |date=1998 |publisher=University of Hawaiʻi Press |isbn=0-8248-2125-4 |page=44 |edition=3rd |quote=Hawaiʻi Island. Hawaiʻi consists of five coalescent, subaerial (above sea level) volcanoes...}}</ref> The oldest volcano on the island, [[Kohala (mountain)|Kohala]], is more than a million years old,<ref>{{cite web |last1=Sherrod |first1=David R. |last2=Sinton |first2=James M. |last3=Watkins |first3=Sarah E. |last4=Brunt |first4=Kelly M. |title=Geologic Map of the State of Hawaiʻi |date=2007 |publisher=United States Geological Survey |location=Reston, Virginia |page=41 |url=https://pubs.usgs.gov/of/2007/1089/Hawaii_expl_pamphlet.pdf}}</ref> and [[Kīlauea]], the youngest, is believed to be between 210,000 and 280,000 years of age.<ref>{{cite web |title=Kīlauea: Geology and History |url=https://www.usgs.gov/volcanoes/kilauea/geology-and-history |website=U.S. Geological Survey |access-date=December 25, 2021}}</ref> [[Kamaʻehuakanaloa Seamount|Kamaʻehuakanaloa]] (formerly Lōʻihi) on the island's flank is even younger, but has yet to breach the surface of the Pacific Ocean.<ref>{{cite book |author1=David A. Clague |author2=David R. Sherrod |editor1-last=Poland |editor1-first=Michael P. |editor2-last=Takahashi |editor2-first=T. Jane |editor3-last=Landowski |editor3-first=Claire M. |title=Characteristics of Hawaiian volcanoes, Professional Paper 1801 |date=2014 |publisher=U.S. Geological Survey |location=Reston, VA |chapter=Growth and degradation of Hawaiian volcanoes|page=104|url=https://pubs.usgs.gov/pp/1801/downloads/pp1801_Chap3_Clague.pdf}}</ref> At 1&nbsp;million to 600,000 years of age,<ref name="USGS-Mauna Loa history">{{cite web|title=Mauna Loa: Earth's Largest Volcano|url=https://www.usgs.gov/volcanoes/mauna-loa/geology-and-history|publisher=Hawaiian Volcano Observatory – [[United States Geological Service]]|access-date=January 29, 2022}}</ref> Mauna Loa is the second youngest of the five volcanoes on the island, making it the [[List of volcanoes in the Hawaiian – Emperor seamount chain|third]] youngest volcano in the [[Hawaiian – Emperor seamount chain]], a chain of [[shield volcano]]es and [[seamount]]s extending from [[Hawaii]] to the [[Kuril–Kamchatka Trench]] in [[Russia]].<ref name="USGS Hotspots">{{cite book|url=https://pubs.usgs.gov/gip/dynamic/hotspots.html|title="Hotspots": Mantle thermal plumes|publisher=United States Geological Survey|edition=1.14|year=1996|isbn=978-0-16-048220-5|author1=W. J. Kious |author2=R. I. Tilling |name-list-style=amp |access-date=December 9, 2012}}</ref>

[[File:mauna loa from hilo bay.JPG|thumb|Mauna Loa from Hilo Bay, December 2017]]

Following the [[Evolution of Hawaiian volcanoes|pattern]] of Hawaiian volcano formation, Mauna Loa would have started as a [[submarine volcano]], gradually building itself up through underwater eruptions of [[alkali]] [[basalt]] before emerging from the sea through a series of [[surtseyan eruption]]s<ref name=hov-evolution>{{cite web|title=Evolution of Hawaiian Volcanoes|url=https://www.usgs.gov/news/volcano-watch-evolution-hawaiian-volcanoes|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 29, 2022|date=March 26, 1998}}</ref> about 400,000 years ago. Since then, the volcano has remained active, with a history of [[Hawaiian eruption|effusive]] and [[explosive eruption|explosive]] eruptions, including 34 eruptions since the first well-documented eruption in 1843.<ref name="hvo-loa">{{cite web |title=Mauna Loa |url=https://www.usgs.gov/volcanoes/mauna-loa |website=US Geological Survey |access-date=January 29, 2022}}</ref>

===Structure===
{{multiple image
| align     = right
| direction = vertical
| width     = 300
| image1    = Mauna Loa Observatory.jpg
| caption1  = Mauna Loa's summit, overlaid with {{convert|100|m|ft|0|abbr=on}} [[contour lines]]; its rift zones are visible from the air.
| image2    = Mokuaweoweo from the air.gif
| caption2  = Mokuʻāweoweo, Mauna Loa's [[caldera|summit caldera]], covered in snow.}}

Mauna Loa is the largest active volcano on Earth and the planet's third largest volcano behind [[Gardner Pinnacles|Pūhāhonu]],<ref name=Garcia2020>{{Cite journal |last1=Garcia |first1=Michael O. |last2=Tree |first2=Jonathan P. |last3=Wessel |first3=Paul |last4=Smith |first4=John R. |date=2020-07-15 |title=Pūhāhonu: Earth's biggest and hottest shield volcano |journal=Earth and Planetary Science Letters |language=en |volume=542 |article-number=116296 |doi=10.1016/j.epsl.2020.116296 |issn=0012-821X|doi-access=free |bibcode=2020E&PSL.54216296G}}</ref> which is also in the Hawaiian chain, and the [[Tamu Massif]].<ref name=tamu>{{cite magazine | magazine = National Geographic | title = New Giant Volcano Below Sea Is Largest in the World | url = http://news.nationalgeographic.com/news/2013/09/130905-tamu-massif-shatsky-rise-largest-volcano-oceanography-science/ | archive-url = https://web.archive.org/web/20130906013208/http://news.nationalgeographic.com/news/2013/09/130905-tamu-massif-shatsky-rise-largest-volcano-oceanography-science/ | archive-date = September 6, 2013 | author = Brian Clark Howard | date = September 5, 2013}}</ref><ref name="ngs">{{Cite journal | journal = Nature Geoscience | volume = 6 | issue = 11 | pages = 976–981 | title = An immense shield volcano within the Shatsky Rise oceanic plateau, northwest Pacific Ocean | last = Sager |first=William W. |author2=Zhang, Jinchang |author3=Korenaga, Jun |author4=Sano, Takashi |author5=Koppers, Anthony A. P. |author6=Widdowson, Mike |author7= Mahoney, John J. | date = September 6, 2013 |doi=10.1038/ngeo1934 | bibcode= 2013NatGe...6..976S}}</ref> It covers a land area of {{convert|5271|km2|mi2|0|abbr=on}} and spans a maximum width of {{convert|120|km|mi|0|abbr=on}}.<ref name="hvo-loa"/> Consisting of approximately {{convert|65000|to|80000|km3|mi3|-2|abbr=on}} of solid rock,<ref name=nps-loa>{{cite web|title=Mauna Loa, Fiery Colossus of the Pacific|author1=G. Macdonald|author2=D. Hubbard|name-list-style=amp|orig-date=1951, 7th ed. revision December 1974|url=http://www.cr.nps.gov/history/online_books/hawaii-notes/vol4-2-7e.htm|publisher=[[National Park Service]]|access-date=December 9, 2012|date=March 24, 2006|archive-url=https://web.archive.org/web/20131020022158/http://www.cr.nps.gov/history/online_books/hawaii-notes/vol4-2-7e.htm|archive-date=October 20, 2013}}</ref> it makes up more than half of the surface area of the island of Hawaiʻi. Combining the volcano's extensive submarine flanks ({{convert|5000|m|ft|-2|abbr=on}} to the sea floor) and {{convert|4170|m|ft|-1|abbr=on}} subaerial height, Mauna Loa rises {{convert|9170|m|ft|0|abbr=on}} from base to summit,<ref name="hvo-loa"/><ref name=soest-loa>{{cite web|title=Mauna Loa Volcano|url=http://www.soest.hawaii.edu/GG/HCV/maunaloa.html|author1=Rubin, Ken |author2= Minicola, Rochelle|publisher=Hawaiian Volcano Observatory – United States Geological Survey|date=March 20, 2009|access-date=December 12, 2012}}</ref> greater than the {{convert|8848|m|ft|0|abbr=on|disp=or}}<ref>{{cite news|title=Nepal in new bid to finally settle Mount Everest height|url=https://www.bbc.co.uk/news/science-environment-17191400|work=[[BBC News]]|access-date=December 10, 2012|author=Navin Singh Khadka|date=February 28, 2012}}</ref> elevation of [[Mount Everest]] from sea level to its summit. In addition, much of the mountain is invisible even underwater: its mass depresses the [[lithosphere|crust]] beneath it by another {{convert|8|km|mi|0|abbr=on}}, in the shape of an inverse mountain,<ref name="gspp">{{cite journal|url=https://books.google.com/books?id=wRosAQAAIAAJ&pg=PA95|title=Subsidence of the Hawaiian Ridge|author=J.G. Moore|journal=Volcanism in Hawaii: Geological Survey Professional Paper| volume= 1350 |issue= 1|year=1987}}</ref> meaning the total height of Mauna Loa from the start of its eruptive history is about {{convert|17170|m|ft|-3|abbr=on}}.<ref>{{cite web|title=How High is Mauna Loa?|url=https://hvo.wr.usgs.gov/volcanowatch/archive/1998/98_08_20.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=February 5, 2013|date=August 20, 1998}}</ref>

{{anchor|Mokuaweoweo}}
[[File:Mauna Loa summit in snow 2016.jpg|thumb|upright=1.36|Snow-covered Moku'aweoweo caldera in 2016]]
Mauna Loa is a typical [[shield volcano]] in form, taking the shape of a long, broad dome extending down to the ocean floor whose slopes are about 12° at their steepest, a consequence of its extremely fluid lava. The shield-stage lavas that built the enormous main mass of the mountain are [[tholeiitic basalt]]s, like those of [[Mauna Kea]], created through the mixing of primary [[magma]] and [[subduction|subducted]] oceanic crust.<ref>{{cite journal|author=Claude Herzberg| title = Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano| journal = [[Nature (journal)|Nature]]| publisher = [[Nature Publishing Group]]| volume = 444| issue = 7119| pages = 605–09| date = November 30, 2006| pmid = 17136091| doi = 10.1038/nature05254 |bibcode = 2006Natur.444..605H | s2cid = 4366221}}</ref> Mauna Loa's summit hosts three overlapping [[pit crater]]s arranged northeast–southwest, the first and last roughly {{convert|1|km|mi|1|abbr=on}} in diameter and the second an oblong {{convert|4.2|x|2.5|km|1|abbr=on}} feature; together these three craters make up the {{convert|6.2|by|2.5|km|mi|1|abbr=on}} summit caldera Mokuʻāweoweo,<ref name=hvo-caldera>{{cite web|title=When did Moku'aweoweo (the summit caldera of Mauna Loa) form?|publisher=Hawaiian Volcano Observatory – United States Geological Survey|url=https://hvo.wr.usgs.gov/volcanowatch/archive/2001/01_03_22.html|access-date=December 11, 2012|date=March 28, 2001}}</ref> so named for the Hawaiian ʻāweoweo fish (''[[Priacanthus meeki]]''), purportedly due to the resemblance of its eruptive fires to the coloration of the fish.<ref>{{cite web|title=Place Names of Hawaii – Moku-ʻāweoweo|url=http://www.wehewehe.org/gsdl2.5/cgi-bin/hdict?a=q&r=1&hs=1&e=q-0hdict--00-0-0--010---4----den--0-000lpm--1haw-Zz-1---Zz-1-home---00031-0000escapewin-00&q=mokuaweoweo&j=pp&hdid=0&hdds=0|archive-url=https://archive.today/20121228082508/http://www.wehewehe.org/gsdl2.5/cgi-bin/hdict?a=q&r=1&hs=1&e=q-0hdict--00-0-0--010---4----den--0-000lpm--1haw-Zz-1---Zz-1-home---00031-0000escapewin-00&q=mokuaweoweo&j=pp&hdid=0&hdds=0|archive-date=December 28, 2012|publisher=Ulukau – Hawaiian Electronic Library|access-date=December 11, 2012}}</ref> Mokuʻāweoweo's caldera floor lies between {{convert|170|and|50|m|0|abbr=on}} beneath its rim and it is only the latest of several calderas that have formed and reformed over the volcano's life. It was created between 1,000 and 1,500 years ago by a large eruption from Mauna Loa's northeast rift zone, which emptied out a shallow [[magma chamber]] beneath the summit and collapsed it into its present form.<ref name=hvo-caldera/> Additionally, two smaller pit craters lie southwest of the caldera, named Lua Hou (New Pit) and Lua Hohonu (Deep Pit).<ref name=nps-loa />

Mauna Loa's summit is also the focal point for its two prominent [[rift zone]]s, marked on the surface by well-preserved, relatively recent lava flows (easily seen in satellite imagery) and linearly arranged [[Fracture (geology)|fracture lines]] intersected by [[cinder cone|cinder]] and [[splatter cone]]s.<ref name=ajs-1980/> These rift zones are deeply set structures, driven by [[dike (geology)|dike]] intrusions along a [[décollement|decollement fault]] that is believed to reach down all the way to the volcano's base, {{convert|12|to|14|km|0|abbr=on}} deep.<ref name=science-stress /> The first is a {{convert|60|km|mi|0|abbr=on}} rift trending southwest from the caldera to the sea and a further {{convert|40|km|mi|0|abbr=on}} underwater, with a prominent 40° directional change along its length; this rift zone is historically active across most of its length. The second, northeastern rift zone extends towards [[Hilo, Hawaii|Hilo]] and is historically active across only the first {{convert|20|km|mi|0|abbr=on}} of its length, with a nearly straight and, in its latter sections, poorly defined trend.<ref name=ajs-1980>{{cite journal|title=The Southwestern Rift Zone of Mauna Kea: Implications for Structural Evolution of Hawaiian Volcanoes|journal=[[American Journal of Science]]|year=1980|volume=280-A|pages=752–76|author=Peter W. Lipman|publisher=American Journal of Science}}</ref> The northeastern rift zone takes the form of a succession of cinder cones, the most prominent of which the {{convert|60|m|ft|0|abbr=on}} high Puu Ulaula, or Red Hill. There is also a less definite northward rift zone that extends towards the Humuula Saddle marking the intersection of Mauna Loa and Mauna Kea.<ref name=nps-loa />

Simplified geophysical models of Mauna Loa's [[magma chamber]] have been constructed, using [[interferometric synthetic aperture radar]] measures of [[Deformation (volcanology)|ground deformation]] due to the slow buildup of lava under the volcano's surface. These models predict a {{convert|1.1|km|mi|0|abbr=on}} wide magma chamber located at a depth of about {{convert|4.7|km|mi|0|abbr=on}}, {{convert|0.5|km|mi|0|abbr=on}} below [[sea level]], near the southeastern margin of Mokuʻāweoweo. This shallow magma chamber is significantly higher-placed than Mauna Loa's rift zones, suggesting magma [[intrusion]]s into the deeper parts and occasional dike injections into the shallower parts of the rift zone drive rift activity; a similar mechanism has been proposed for neighboring [[Kīlauea]].<ref name=science-stress /> Earlier models, based on Mauna Loa's 1975 and 1984 eruptions, made a similar prediction, placing the chamber at {{convert|3|km|mi|1|abbr=on}} deep in roughly the same geographic position.<ref>{{cite web|title=What's up with Mauna Loa?|url=https://hvo.wr.usgs.gov/volcanowatch/archive/2001/01_10_18.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=December 16, 2012|date=October 23, 2001|archive-url=https://web.archive.org/web/20120919133433/https://hvo.wr.usgs.gov/volcanowatch/archive/2001/01_10_18.html|archive-date=September 19, 2012}}</ref>

Mauna Loa has complex interactions with its neighbors, [[Hualālai]] to the northwest, [[Mauna Kea]] to the northeast, and particularly [[Kīlauea]] to the east. Lavas from Mauna Kea intersect with Mauna Loa's basal flows as a consequence of Kea's older age,<ref name="pp1557">{{cite book|author1=E. W. Wolfe|author2=W. S. Wise|author3=G. B. Dalrymple|title=The geology and petrology of Mauna Kea volcano, Hawaii: a study of postshield volcanism|url=https://pubs.er.usgs.gov/djvu/PP/pp_1557.djvu|series=Professional Paper 1557|year=1997|publisher=United States Geological Survey|access-date=December 12, 2012|archive-date=June 15, 2011|archive-url=https://web.archive.org/web/20110615111115/http://http/}}</ref> and Mauna Kea's original [[rift zone]]s were buried beneath post-shield volcanic rocks of Mauna Loa;<ref name="usgs-database">{{cite web|title=Complete Report for Mauna Kea Volcano (Class B) No. 2601 |url=https://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?disp_cd=C&qfault_or=5107&ims_cf_cd=cf |publisher=United States Geological Survey |access-date=December 12, 2012 |author1=E. C. Cannon |author2=R. R. Bürgmann |name-list-style=amp |date=October 26, 2009 |archive-url=https://web.archive.org/web/20120305184251/http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?disp_cd=C&qfault_or=5107&ims_cf_cd=cf |archive-date=March 5, 2012}}</ref> additionally, Mauna Kea shares Mauna Loa's gravity well, depressing the [[oceanic lithosphere|ocean crust]] beneath it by {{convert|6|km|mi|0|abbr=on}}.<ref name="pp1557"/>  There are also a series of [[normal fault]]s on Mauna Loa's northern and western slopes, between its two major rift zones, that are believed to be the result of combined circumferential tension from the two rift zones and from added pressure due to the westward growth of neighboring Kīlauea.<ref name=osu-rifts>{{cite web|title=Rift Zones|url=http://volcano.oregonstate.edu/book/export/html/124|publisher=[[Oregon State University]]|access-date=December 13, 2012}}</ref>

[[File:Volcano in Moonlight.jpg|thumb|right|upright=1.6|Captured from Maunakea, this Image features a skyscape of Mauna Loa.<ref>{{cite news|title=Volcano in Moonlight|url=https://noirlab.edu/public/images/iotw2234a/?nocache=true|access-date=26 December 2022|newspaper=NOIRLab}}</ref>]]
Because Kīlauea lacks [[topographical prominence]] and appears as a bulge on the southeastern flank of Mauna Loa, it was historically interpreted by both native Hawaiians and early geologists to be an active satellite of Mauna Loa. However, analysis of the chemical composition of lavas from the two volcanoes show that they have separate [[magma chamber]]s, and are thus distinct. Nonetheless, their proximity has led to a historical trend in which high activity at one volcano roughly coincides with low activity at the other. When Kīlauea lay dormant between 1934 and 1952, Mauna Loa became active, and when the latter remained quiet from 1952 to 1974, the reverse was true. This is not always the case; the [[1984 eruption of Mauna Loa]] started during an eruption at Kīlauea, but had no discernible effect on the Kīlauea eruption, and the [[2022 eruption of Mauna Loa]] occurred during an eruption of Kīlauea. Geologists have suggested that "pulses" of magma entering Mauna Loa's deeper magma system may have increased pressure inside Kīlauea and triggered the concurrent eruptions.<ref name="hvo-loa_kilauea">{{cite web|title=Inflation of Mauna Loa Volcano slows|publisher=Hawaiian Volcano Observatory – United States Geological Survey|work=Volcano Watch|date=January 28, 2003|url=https://hvo.wr.usgs.gov/volcanowatch/2003/03_01_23.html|access-date=January 30, 2012}}</ref>

Mauna Loa is slumping eastward along its southwestern rift zone, leveraging its mass into Kīlauea and driving the latter eastward at a rate of about {{convert|10|cm|in|0|abbr=on}} per year; the interaction between the two volcanoes in this manner has generated a number of large earthquakes in the past, and has resulted in a significant area of debris off Kīlauea's seaward flank known as the [[Hilina Slump]]. A system of older faults exists on the southeastern side of Mauna Loa that likely formed before Kilauea became large enough to impede Mauna Loa's slump, the lowest and northernmost of which, the Kaoiki fault, remains an active earthquake center today. The west side of Mauna Loa, meanwhile, is unimpeded in movement, and indeed is believed to have undergone a massive slump collapse between 100,000 and 200,000 years ago, the residue from which, consisting of a scattering of debris up to several kilometers wide and up to {{convert|50|km|mi|0|abbr=on}} distant, is still visible today. The damage was so extensive that the headwall of the damage likely intersected its southwestern rift zone. There is very little movement there today, a consequence of the volcano's geometry.<ref name="uh-landslides">{{cite web |author=Ken Hon |author-link=Ken Hon |title=Giant Landslides: Kilauea and Mauna Loa: GEOL 205: Lecture Notes |url=http://hilo.hawaii.edu/~kenhon/GEOL205/Landslides/default.htm |access-date=December 16, 2012 |publisher=[[University of Hawaii at Hilo]]}}</ref>

[[File:Mauna Loa taken from the 9300 ft level on the ascent of Mauna Kea.JPG|thumb|right|upright=1.6|A view of Mauna Loa taken from a hill near The Onizuka Center for International Astronomy Visitor Information Station at the {{convert|9,300|ft|m|abbr=on}} level of Mauna Kea.]]
Mauna Loa is tall enough to have experienced [[glaciation]] during the last ice age, 25,000 to 15,000 years ago.<ref name=usgs-map /> Unlike Mauna Kea, on which extensive evidence of glaciation remains even today,<ref>{{cite web|url=https://hvo.wr.usgs.gov/volcanowatch/archive/2001/01_10_18.html|title=Glaciers on Mauna Kea? You crazy? In the middle of the Pacific? YES!|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=December 16, 2012|date=October 22, 2007}}</ref> Mauna Loa was at the time and has remained active, having grown an additional {{convert|150|to|300|m|ft|0|abbr=on}} in height since then and covering any glacial deposits beneath new flows; strata of that age don't occur until at least {{convert|2000|m|ft|0|abbr=on}} down from the volcano's summit, too low for glacial growth. Mauna Loa also lacks its neighbor's summit [[permafrost]] region, although sporadic ice persists in places. It is speculated that extensive [[phreatomagmatic eruption|phreatomagmatic]] activity occurred during this time, contributing extensively to [[volcanic ash|ash]] deposits on the summit.<ref name=usgs-map />
{{clear}}

==Eruptive history==
{{see also|List of Mauna Loa eruptions}}

===Prehistoric eruptions===
[[File:Mauna Loa from the air.jpg|thumb|right|A [[cinder cone]] and surrounding flows on Mauna Loa]]
To have reached its enormous size within its relatively short (geologically speaking) 600,000 to 1,000,000 years of life, Mauna Loa would logically have had to have grown extremely rapidly through its developmental history,<ref name=hvo-erupt /> and extensive [[charcoal]]-based [[radiocarbon dating]] (perhaps the most extensive such prehistorical eruptive dating on Earth<ref name=soest-erupt /><ref name=hvo-model>{{cite web|title=Eruption History: A Cyclic Eruption Model is Proposed|url=https://hvo.wr.usgs.gov/maunaloa/history/model.html|publisher=HVO|access-date=December 25, 2012|date=March 16, 1998|archive-date=August 21, 2007|archive-url=https://web.archive.org/web/20070821145956/http://hvo.wr.usgs.gov/maunaloa/history/model.html}}</ref>) has amassed a record of almost two hundred<!-- ~200 in the 2006 HVO eruption summary, 170 is the older 1980s era papers --> reliably dated extant flows confirming this hypothesis.<ref name=hvo-erupt />

Lava samples, including those obtained by drilling projects, have been dated at least to 470,000&nbsp;years ago.<ref name=Jicha2012/> For technical reasons the oldest ages obtained by modern techniques at 657,000&nbsp;years ago have large errors of the order of 200,000&nbsp;years, as did some historic dating attempts on younger lavas making them older than was the case.<ref name=Jicha2012/>{{rp|loc=Conclusions}} Some of the oldest exposed flows on Mauna Loa are the Ninole Hills on its southern flank, subaerial [[basalt]] rock dating back approximately 100 to 200 thousand years.<ref name=Jicha2012/> They form a terrace against which younger flows have since banked, heavily eroded and incised against its slope in terms of direction; this is believed to be the result of a period of erosion because of a change in the direction of lava flow caused by the volcano's prehistoric slump. These are followed by two units of lava flows separated by an intervening [[volcanic ash|ash]] layer known as the Pāhala ash layer: the older Kahuka basalt, sparsely exposed on the lower southwest rift, and the younger and far more widespread Kaʻu basalt, which appear more widely on the volcano. The Pāhala ashes themselves were produced over a long period of time circa 13 to 30 thousand years ago, although heavy [[vitrification]] and interactions with post- and pre- creation flows has hindered exact dating. Their age roughly corresponds to the glaciation of Mauna Loa during the last ice age, raising the distinct possibility that it is the product of [[phreatomagmatic eruption|phreatomagmatic]] interaction between the long-gone glaciers and Mauna Loa's eruptive activities.<ref name=usgs-map />

Studies have shown that a cycle occurs in which volcanic activity at the summit is dominant for several hundred years, after which activity shifts to the rift zones for several more centuries, and then back to the summit again. Two cycles have been clearly identified, each lasting 1,500–2,000&nbsp;years. This cyclical behavior is unique to Mauna Loa among the Hawaiian volcanoes.<ref>Lockwood J.P. (1995), "Mauna Loa eruptive history – the preliminary radiocarbon record", in Rhodes, J.M. and Lockwood, J.P. (eds.), ''Mauna Loa revealed: structure, composition, history, and hazards'', Washington D.C., American Geophysical Union Monograph 92, pp. 81–94.</ref> Between about 7,000 and 6,000&nbsp;years ago Mauna Loa was largely inactive. The cause of this cessation in activity is not known, and no known similar hiatus has been found at other Hawaiian volcanoes except for those currently in the post-shield stage. Between 11,000 and 8,000&nbsp;years ago, activity was more intense than it is today.<ref name=soest-erupt /> However, Mauna Loa's overall rate of growth has probably begun to slow over the last 100,000&nbsp;years,<ref>{{cite web | url = https://hvo.wr.usgs.gov/maunaloa/history/main.html | title = Eruption History of Mauna Loa Volcano | publisher = United States Geological Survey, Hawaiian Volcano Observatory | access-date = July 28, 2007 | archive-date = August 19, 2007 | archive-url = https://web.archive.org/web/20070819083329/http://hvo.wr.usgs.gov/maunaloa/history/main.html }}</ref> and the volcano may in fact be nearing the end of its [[tholeiite|tholeiitic basalt]] shield-building phase.<ref>{{cite web | url = https://hvo.wr.usgs.gov/maunaloa/history/model.html | title = Eruption History: A Cyclic Eruption Model is Proposed | publisher = United States Geological Survey, Hawaiian Volcano Observatory | date = March 16, 1998 | access-date = July 28, 2007 | archive-date = August 21, 2007 | archive-url = https://web.archive.org/web/20070821145956/http://hvo.wr.usgs.gov/maunaloa/history/model.html }}</ref>

=== Recent history ===
[[File:Aa channel flow from Mauna Loa.jpg|thumb|Lava fountains and [[Lava#ʻAʻā|a'a]] channel flow from Mauna Loa, 1984]]
[[Ancient Hawaii]]ans have been present on Hawaiʻi island for about 1,500 years, but they preserved almost no records on volcanic activity on the island, beyond a few fragmentary accounts dating to the late 18th and early 19th centuries.<ref name=hvo-erupthist>{{cite web|title=Summary of Historical Eruptions, 1843–Present|url=https://hvo.wr.usgs.gov/maunaloa/history/historytable.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013|date=September 17, 2004|archive-date=August 13, 2007|archive-url=https://web.archive.org/web/20070813100729/http://hvo.wr.usgs.gov/maunaloa/history/historytable.html}}</ref>  Possible eruptions occurred around 1730 and 1750 and sometime during 1780<!-- according to a travel guide on the Wilkes expedition -  see the SOEST eruptive history reference --> and 1803.<ref>{{cite gvp|title=Mauna Loa: Eruptive History|vn=332020|vtab=Eruptions|access-date=January 24, 2013}}</ref> A June 1832 eruption was witnessed by a missionary on [[Maui]], but the {{convert|190|km|mi|0|abbr=on}} between the two islands and lack of apparent geological evidence have cast this testimony in doubt. Thus the first entirely confirmed historically witnessed eruption was a January 1843 event; since that time Mauna Loa has erupted 32 times.<ref name=hvo-erupthist />

Historical eruptions at Mauna Loa are typically [[Hawaiian eruption|Hawaiian]] in character and rarely violent, starting with the emergence of [[lava fountain]]s over a several kilometer long [[rift]] colloquially known as the "curtain of fire" (often, but not always, propagating from Mauna Loa's summit<ref name=science-stress>{{cite journal|title=Stress Control of Deep Rift Intrusion at Mauna Loa Volcano, Hawaii|journal=[[Science (journal)|Science]]|date=May 18, 2007|volume=316|issue=5827|pages=1026–30|doi =10.1126/science.1140035|first1=F.|last1=Amelung|first2 =S.H.|last2=Yun|first3 =T.R.|last3 =Walter|first4 =P.|last4 =Segall|first5 =S.W.|last5 =Kim|publisher=[[American Association for the Advancement of Science]]|bibcode = 2007Sci...316.1026A |pmid=17510364|s2cid=39726145}}</ref>) and eventually concentrating at a single vent, its long-term eruptive center.<ref name=nps-loa/><ref name=ajs-1980 /> Activity centered on its summit is usually followed by flank eruptions up to a few months later,<ref name=hvo-hist-loa /> and although Mauna Loa is historically less active than that of its neighbor Kilauea, it tends to produce greater volumes of lava over shorter periods of time.<ref name=usgs-hazard/> Most eruptions are centered at either the summit or either of its two major [[rift zone]]s; within the last two hundred years, 38 percent of eruptions occurred at the summit, 31 percent at the northeast rift zone, 25 percent at the southwest rift zone, and the remaining 6 percent from northwest vents.<ref name=soest-erupt>{{cite web|title=Mauna Loa Eruption History|url=http://www.soest.hawaii.edu/GG/HCV/mloa-eruptions.html|publisher=[[Hawaii Center for Volcanology]]|access-date=December 12, 2012|author1=Rubin, Ken|author2=Minicola, Rochelle|date=March 7, 2007}}</ref> 40 percent of the volcano's surface consists of lavas less than a thousand years old,<ref name=usgs-hazard>{{cite web|title=Lava Flow Hazard Zone Maps: Mauna Loa|url=https://pubs.usgs.gov/gip/hazards/mauna-loa.html|publisher=United States Geological Survey|access-date=December 12, 2012|author=John Watson|date=July 18, 1997|archive-url=https://web.archive.org/web/20130115203408/http://pubs.usgs.gov/gip/hazards/mauna-loa.html|archive-date=January 15, 2013}}</ref> and 98 percent of lavas less than 10,000 years old.<ref name=hvo-erupt>{{cite web|title=Eruption History|url=https://hvo.wr.usgs.gov/maunaloa/history/main.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=December 16, 2012|date=February 2, 2006|archive-date=August 19, 2007|archive-url=https://web.archive.org/web/20070819083329/http://hvo.wr.usgs.gov/maunaloa/history/main.html}}</ref> In addition to the summit and rift zones, Mauna Loa's northwestern flank has also been the source of three historical eruptions.<ref name=usgs-hazard/>

The 1843 event was followed by eruptions in 1849, 1851, 1852, and 1855,<ref name=hvo-erupthist /> with the 1855 flows being particularly extensive.<ref name=soest-erupt /> 1859 marked the largest of the three historical flows that have been centered on Mauna Loa's northwestern flank, producing a long lava flow that reached the ocean on Hawaii island's west coast, north of [[Kiholo bay|Kīholo Bay]].<ref name=usgs-hazard/> An eruption in 1868 occurred alongside the enormous [[1868 Hawaii earthquake]],<ref name=soest-erupt /> a [[moment magnitude|magnitude]] eight event that claimed 77 lives and remains the largest earthquake ever to hit the island.<ref>{{cite web|title=The Great Ka'u Earthquake of 1868|url=https://hvo.wr.usgs.gov/volcanowatch/archive/1994/94_04_01.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013|date=March 26, 1998}}</ref> Following further activity in 1871, Mauna Loa experienced nearly continuous activity from August 1872 through 1877, a long-lasting and voluminous eruption lasting approximately 1,200 days and never moving beyond its summit.<ref name=hvo-erupthist /><ref>{{cite web|title=Eruptions of Hawaiian Volcanoes|url=https://pubs.usgs.gov/gip/hawaii/page15.html|publisher=United States Geological Survey|access-date=January 24, 2013|date=January 5, 1997}}</ref><ref name=hvo-1950>{{cite web|title=50th Anniversary of Mauna Loa's Most Spectacular Eruption|url=https://hvo.wr.usgs.gov/maunaloa/history/50_06_01/|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013|date=September 17, 2004|archive-date=January 30, 2013|archive-url=https://web.archive.org/web/20130130173304/http://hvo.wr.usgs.gov/maunaloa/history/50_06_01/}}</ref> A short single-day eruption in 1877 was unusual in that it took place underwater, in [[Kealakekua Bay]], and within a mile of the shoreline; curious onlookers approaching the area in boats reported unusually turbulent water and occasional floating blocks of hardened lava.<ref name=usgs-hazard/> Further eruptions occurred in 1879 and then twice in 1880,<ref name=hvo-erupthist /> the latter of which extended into 1881 and came within the present boundaries of the island's largest city, [[Hilo]]; however, at the time, the settlement was a shore-side village located further down the volcano's slope, and so was unaffected.<ref name=soest-erupt /><ref name=usgs-hazard/><ref>{{Cite book|url=https://books.google.com/books?id=YIE9AQAAIAAJ&q=carbonic+oxide|title=Scientific American|date=August 13, 1881|publisher=Munn & Company|page=106|language=en}}</ref>

<imagemap>
File:Hawaii Volcanoes Hazard Map.svg|thumb|right|275px|Clickable imagemap of the United States Geological Survey [[Lava Flow Hazard Zones|hazard mapping]] for Hawaii island; the lowest numbers correspond with the highest hazard levels.

poly 25 186 49 180 73 150 54 108 36 100 24 104 5 123 3 137 22 164 [[Hualalai]]
poly 54 64 99 63 113 40 78 23 74 12 46 5 37 21 41 44 [[Kohala (mountain)|Kohala]]
poly 247 157 236 157 203 198 172 202 149 230 128 277 173 250 193 248 249 226 287 186 259 173 [[Kilauea]]
poly 56 65 99 64 116 38 188 66 224 103 221 134 194 140 139 143 93 123 60 92 53 79 [[Mauna Kea]]

desc bottom-left
</imagemap>

Mauna Loa continued its activity, and of the eruptions that occurred in 1887, 1892, 1896, 1899, 1903 (twice), 1907, 1914, 1916, 1919, and 1926,<ref name=hvo-erupthist /> three (in 1887, 1919, and 1926) were partially [[subaerial]].<ref name=soest-erupt /> The 1926 eruption in particular is noteworthy for having inundated a village near Ho{{okina}}ōpūloa, destroying 12 houses, a church, and a small harbor.<ref name="hvo-1926">{{cite web|title=The Mauna Loa Eruption of 1926|url=https://hvo.wr.usgs.gov/volcanowatch/archive/1995/95_04_07.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|date=March 26, 1998}}</ref> After an event in 1933, Mauna Loa's 1935 eruption caused a public crisis when its flows started to head towards Hilo.<ref name=hvo-erupthist /> A bombing operation was decided upon to try and divert the flows, planned out by then-[[lieutenant colonel]] [[George S. Patton]]. The bombing, conducted on December 27, was declared a success by [[Thomas A. Jaggar]], director of the Hawaiian Volcano Observatory, and lava stopped flowing by January 2, 1936. However, the role the bombing played in ending the eruption has since been heavily disputed by volcanologists.<ref>{{cite web|title=Lava diversion in Hawaiʻi?|url=https://hvo.wr.usgs.gov/volcanowatch/archive/1997/97_11_28.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013}}</ref> A longer but summit-bound event in 1940 was comparatively less interesting.<ref name=hvo-erupthist />

Mauna Loa's 1942 eruption occurred only four months after the [[attack on Pearl Harbor]] and the United States' entry into [[World War II]], and created a unique problem for the wartime United States. Occurring during an enforced nighttime [[Blackout (wartime)|blackout]] on the island, the eruption's luminosity forced the government to issue a [[gag order]] on the local press, hoping to prevent news of its occurrence spreading, for fear that the Japanese would use it to launch a bombing run on the island. However, as flows from the eruption rapidly spread down the volcano's flank and threatened the ʻOlaʻa [[flume]], [[Mountain View, Hawaii|Mountain View]]'s primary [[water source]], the [[United States Army Air Forces|United States Army Air Force]] decided to drop its own bombs on the island in the hopes of redirecting the flows away from the flume; sixteen bombs weighing between {{convert|300|and|600|lb|kg|0|abbr=on}} each were dropped on the island, but produced little effect. Eventually, the eruption ceased on its own.<ref>{{cite web|title=Shhh! Don't tell there is an eruption – Eruption of 1942|url=https://volcanoes.usgs.gov/observatories/hvo/hvo_volcano_watch.html?vwid=970|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013|date=April 27, 1998}}</ref>

Following a 1949 event, the next major eruption at Mauna Loa occurred in 1950. Originating from the volcano's southwestern rift zone, the eruption remains the largest rift event in the volcano's modern history, lasting 23 days, emitting 376&nbsp;million cubic meters of lava, and reaching the {{convert|24|km|mi|0|abbr=on}} distant ocean within 3 hours. The 1950 eruption was not the most voluminous eruption on the volcano (the long-lived 1872–1877 event produced more than twice as much material), but it was easily one of the fastest-acting, producing the same amount of lava as the 1859 eruption in a tenth of the time.<ref name=hvo-1950/> Flows overtook the village of Hoʻokena-mauka in [[South Kona, Hawaii|South Kona]], crossed [[Hawaii Belt Road|Hawaii Route 11]], and reached the sea within four hours of eruption. Although there was no loss of life, the village was permanently destroyed.<ref>{{cite web|title=The 1950 eruption of Mauna Loa: a nightmare that could reoccur|url=https://www.usgs.gov/center-news/volcano-watch-1950-eruption-mauna-loa-a-nightmare-could-reoccur|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=February 2, 2021|date=May 14, 2001}}</ref> After the 1950 event, Mauna Loa entered an extended period of dormancy, interrupted only by a [[1975 eruption of Mauna Loa|small single-day summit event in 1975]]. However, it rumbled to life again in 1984, manifesting first at Mauna Loa's summit, and then producing a narrow, channelized [['a'a|ʻaʻā]] flow that advanced downslope within {{convert|6|km|mi|0|abbr=on}} of Hilo, close enough to illuminate the city at nighttime. However, the flow got no closer, as two natural levees further up its pathway consequently broke and diverted active flows.<ref>{{cite web|title=The Mauna Loa Eruption of 1984|url=https://hvo.wr.usgs.gov/volcanowatch/archive/1994/94_03_25.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 24, 2013|date=March 26, 1998}}</ref><ref>{{cite web|title=1984 Eruption: March 25 – April 15|url=https://hvo.wr.usgs.gov/maunaloa/history/1984.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|date=September 17, 2004|access-date=January 24, 2013|archive-date=January 31, 2013|archive-url=https://web.archive.org/web/20130131132038/http://hvo.wr.usgs.gov/maunaloa/history/1984.html}}</ref>

From 1985 to 2022, the volcano had its longest period of quiet in recorded history.<ref name=hvo-erupthist/><ref name="npsbrochure">{{cite web |author-link1=Gordon A. Macdonald |author1=Gordon A. Macdonald |author2=Douglass H. Hubbard |title=Volcanoes of the National Parks of Hawaii |url=http://www.nps.gov/history/history/online_books/hawaii-notes/vol4-2-7d.htm |archive-url=https://web.archive.org/web/20080509055809/http://www.nps.gov/history/history/online_books/hawaii-notes/vol4-2-7d.htm |archive-date=May 9, 2008 |publisher=[[National Park Service]] |date=March 24, 2006 |access-date=January 24, 2013}}</ref> Magma had been accumulating beneath Mauna Loa since the 1984 eruption, and the U.S. Geological Survey in February 2021 reported that although an eruption "did not appear to be imminent," the volcano had shown elevated signs of unrest since 2019, including a slight increase in the rate of inflation at the volcano's summit.<ref>{{cite web |title=Volcano Watch — When will Mauna Loa erupt next? |url=https://www.usgs.gov/observatories/hvo/news/volcano-watch-when-will-mauna-loa-erupt-next |website=U.S. Geological Survey |date=February 25, 2021}}</ref>

The quiet period ended at 11:30&nbsp;pm [[Hawaii–Aleutian Time Zone|HST]] on November 27, 2022, when [[2022 eruption of Mauna Loa|an eruption]] began at the volcano's summit in Moku'āweoweo (Mauna Loa's caldera).<ref name=hvo-loa-2022/> Lava flows emanating from the caldera became visible from&nbsp;[[Kailua-Kona]] in the hours immediately following the eruption. The eruption remained confined to the caldera until approximately 6:30&nbsp;am HST on November 28, when the Hawaiian Volcano Observatory observed that the eruption had migrated from the summit to the Northeast Rift Zone.<ref>{{Cite web |title=HAWAIIAN VOLCANO OBSERVATORY VOLCANO OBSERVATORY NOTICE FOR AVIATION Monday, November 28, 2022, 17:20 UTC USGS Hazard Notification System (HANS) for Volcanoes |url=https://volcanoes.usgs.gov/hans2/view/notice/DOI-USGS-HVO-2022-11-28T09:00:26-08:00 |access-date=2022-11-29 |website=volcanoes.usgs.gov}}</ref> Three fissures were initially observed in the rift zone, with the first two becoming inactive by 1:30 PM on the 28th. Before becoming inactive, the two upper fissures fed lava flows that moved downslope, however those flows stalled approximately {{convert|11|mi|km}} from [[Saddle Road]]. [[Lava|Lava fountains]] were also observed emanating from the fissures, with the tallest reaching up to {{convert|200|ft|m}} into the air.<ref>{{Cite web |title=HAWAIIAN VOLCANO OBSERVATORY STATUS REPORT Tuesday, November 29, 2022, 02:55 UTC USGS Hazard Notification System (HANS) for Volcanoes |url=https://volcanoes.usgs.gov/hans2/view/notice/DOI-USGS-HVO-2022-11-28T18:29:33-08:00 |access-date=2022-11-30 |website=volcanoes.usgs.gov}}</ref> As lava flows from the third fissure expanded, they cut off the road to the [[Mauna Loa Observatory]] at approximately 8&nbsp;pm on the 28th. Activity in the rift zone continued on the 29th, with a fourth fissure that opened at approximately 7:30&nbsp;pm on the 28th joining the third in releasing lava flows. The main front of the third fissure's lava flows also continued to move, and was located approximately {{convert|2.7|mi|km}} from Saddle Road at 7&nbsp;am on December 2. 

As the eruption approached its second week, indications of a reduction in activity began to appear. On December 8, the lava flows feeding the main front began to drain, and the main flow front stalled approximately {{convert|1.7|mi|km}} from Saddle Road. The flows continued to drain on the 9th, and the third fissure's lava fountains also began to grow shorter. On the 10th, the lava fountains were replaced by a lava pond, and the stalled flow front was declared to no longer be a threat. Based on these factors and data on past eruptions, the HVO determined that the eruption may end soon and reduced the [[Volcano warning schemes of the United States|volcano alert level]] from Warning to Watch at 2:35&nbsp;pm on the 10th. However, there was a small possibility that the eruption would continue at a very low rate.<ref>{{Cite web |title=HAWAIIAN VOLCANO OBSERVATORY VOLCANO ACTIVITY NOTIFICATION Sunday, December 11, 2022, 00:35 UTC USGS Hazard Notification System (HANS) for Volcanoes |url=https://volcanoes.usgs.gov/hans2/view/notice/DOI-USGS-HVO-2022-12-10T16:24:56-08:00 |access-date=2022-12-11 |website=volcanoes.usgs.gov}}</ref> The eruption officially ended at 7:17&nbsp;am on the 13th, and the HVO lowered the volcano alert level to Advisory.<ref>{{Cite web |title=HAWAIIAN VOLCANO OBSERVATORY VOLCANO OBSERVATORY NOTICE FOR AVIATION Tuesday, December 13, 2022, 17:17 UTC USGS Hazard Notification System (HANS) for Volcanoes |url=https://volcanoes.usgs.gov/hans2/view/notice/DOI-USGS-HVO-2022-12-13T08:57:10-08:00 |access-date=2022-12-16 |website=volcanoes.usgs.gov}}</ref>

===Hazards===
Mauna Loa has been designated a [[Decade Volcano]], one of the sixteen volcanoes identified by the [[International Association of Volcanology and Chemistry of the Earth's Interior]] (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas.<ref>{{cite web|url=https://vulcan.wr.usgs.gov/Volcanoes/DecadeVolcanoes/|title=Decade Volcanoes|work=[[Cascades Volcano Observatory]]|author=International Association of Volcanology and Chemistry of the Earth's Interior|publisher=United States Geological Survey|year=1998|access-date=January 25, 2013|author-link=International Association of Volcanology and Chemistry of the Earth's Interior}}</ref><ref>{{cite web|title=Decade Volcano Program IDNDR – IAVCEI – 1990/2000|url=http://www.sveurop.org/gb/program/program.htm|publisher=Société Volcanologique Européenne|author=Nick Varley|access-date=January 25, 2013}}</ref> The United States Geological Survey maintains a [[Lava Flow Hazard Zones|hazard zone mapping]] of the island done on a one to nine scale, with the most dangerous areas corresponding the smallest numbers. Based on this classification Mauna Loa's continuously active summit caldera and rift zones have been given a level one designation. Much of the area immediately surrounding the rift zones is considered level two, and about 20 percent of the area has been covered in lava in historical times. Much of the remainder of the volcano is hazard level three, about 15 to 20 percent of which has been covered by flows within the last 750 years. However, two sections of the volcano, the first in the [[Naalehu, Hawaii|Naalehu]] area and the second on the southeastern flank of Mauna Loa's rift zone, are protected from eruptive activity by local topography, and have thus been designated hazard level 6, comparable with a similarly isolated segment on [[Kīlauea]].<ref name="usgs-hazard" />

Although volcanic eruptions in Hawaiʻi rarely produce casualties (the only direct historical fatality due to volcanic activity on the island occurred at Kīlauea in 1924, when an unusually explosive eruption hurled rocks at an onlooker), property damage due to inundation by lava is a common and costly hazard.<ref name="usgs-hazard_all">{{cite web | author = John Watson | title = Volcanic and seismic hazards on the island of Hawaii | publisher = United States Geological Survey | url = https://pubs.usgs.gov/gip/hazards/hazards.html | date = July 18, 1997 | access-date = January 25, 2013 | archive-date = January 15, 2013 | archive-url = https://web.archive.org/web/20130115203420/http://pubs.usgs.gov/gip/hazards/hazards.html }}</ref> [[Hawaiian eruption|Hawaiian]]-type eruptions usually produce extremely slow-moving flows that advance at walking pace, presenting little danger to human life, but this is not strictly the case;<ref>{{cite web|title=How Volcanoes Work: Hawaiian Eruptions|url=http://www.geology.sdsu.edu/how_volcanoes_work/Hawaiian.html|publisher=[[San Diego State University]]|access-date=January 25, 2013}}</ref> Mauna Loa's 1950 eruption emitted as much lava in three weeks as Kīlauea's [[Kīlauea#1983–2018|recent eruption]] produced in three years and reached sea level within four hours of its start, overrunning the village of Hoʻokena Mauka and a major highway on the way there.<ref name=hvo-1950 /> An earlier eruption in 1926 overran the village of Hoʻōpūloa Makai,<ref name="hvo-1926" /> and [[Hilo, Hawaii|Hilo]], partly built on lavas from the 1880–81 eruption, is at risk from future eruptions.<ref name=usgs-hazard/> The 1984 eruption nearly reached the city, but stopped short after the flow was redirected by upstream topography.<ref name="usgs-loa_hazards">{{cite web | url = https://hvo.wr.usgs.gov/maunaloa/hazards/main.html | title = Lava flow hazards on Mauna Loa volcano | publisher = Hawaiian Volcano Observatory – United States Geological Survey | date = February 2, 2006 | access-date = January 25, 2013}}</ref>

A potentially greater hazard at Mauna Loa is a sudden, massive collapse of the volcano's flanks, like the one that struck the volcano's west flank between 100,000 and 200,000 years ago and formed the present-day [[Kealakekua Bay]].<ref name=uh-landslides/> Deep [[Fault (geology)|fault lines]] are a common feature on Hawaiian volcanoes, allowing large portions of their flanks to gradually slide downwards and forming structures like the [[Hilina Slump]] and the ancient [[Ninole Hills]]; large earthquakes could trigger rapid flank collapses along these lines, creating massive [[volcanic landslide|landslides]] and possibly triggering equally large [[tsunami]]s. Undersea surveys have revealed numerous landslides along the Hawaiian chain and evidence of two such giant tsunami events: 200,000&nbsp;years ago, [[Molokai|Molokaʻi]] experienced a {{convert|75|m|ft|0|abbr=on}} tsunami, and 100,000&nbsp;years ago a [[megatsunami]] {{convert|325|m|ft|0|abbr=on}} high struck [[Lanai|Lānaʻi]].<ref name="Decker">{{Cite book|author=Robert and Barbara Decker|title=Volcanoes|url=https://archive.org/details/volcanoes00deck_0|url-access=registration|year=1997|publisher=W.H. Freeman & Co, Ltd|location=New York|isbn=978-0-7167-3174-0|edition=3rd}}</ref> A more recent example of the risks associated with slumps occurred in [[1975 Hawaii earthquake|1975]], when the Hilina Slump suddenly lurched forward several meters, triggering a 7.2 {{M|w}} earthquake and a {{convert|14|m|abbr=on}} tsunami that killed two campers at Halape.<ref>{{cite journal|title=Shallow Normal Faulting and Block Rotation Associated with the 1975 Kalapana Earthquake, Kilauea'|journal=[[Bulletin of the Seismological Society of America]]|year=2001|volume=91|issue=6|page=1553|doi=10.1785/0120000072|author1=Cannon, Eric C.|author2=Bürgmann, Roland|author3=Owen, Susan E.|publisher=[[Seismological Society of America]]|bibcode = 2001BuSSA..91.1553C}}</ref>

===Monitoring===
{{multiple image
| align     = right
| direction = horizontal
| image1    = Mauna Loa Summit Monitoring.jpg
| width1    = 205
| caption1  = [[GPS]] stations, [[tiltmeter]]s, and [[strainmeter]]s on Mauna Loa's summit. Not shown: a [[webcam]] and a [[gas detector]] positioned on the caldera rim.
| image2    = Mauna Loa Summit Inflation.jpg
| width2     = 225
| caption2  = Summit inflation as measured via [[GPS]] between June 2004 and April 2005; arrows denote between {{convert|1|and|10|cm|in|1|abbr=on}} of growth.
}}

Established on Kīlauea in 1912, the Hawaiian Volcano Observatory (HVO), presently a branch of the United States Geological Survey, is the primary organization associated with the monitoring, observance, and study of Hawaiian volcanoes.<ref name=hvo-hist-intro>{{cite web|title=Thomas A. Jaggar, Jr., and the Hawaiian Volcano Observatory|url=https://hvo.wr.usgs.gov/observatory/hvo_history.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|author=Russell A. Apple|date=January 4, 2005|archive-date=June 14, 2009|archive-url=https://web.archive.org/web/20090614054515/http://hvo.wr.usgs.gov/observatory/hvo_history.html}}</ref> [[Thomas A. Jaggar]], the Observatory's founder, attempted a summit expedition to Mauna Loa to observe its 1914 eruption, but was rebuffed by the arduous trek required (see [[#Ascents|Ascents]]). After soliciting help from [[Lorrin A. Thurston]], in 1915 he was able to persuade the [[US Army]] to construct a "simple route to the summit" for public and scientific use, a project completed in December of that year; the Observatory has maintained a presence on the volcano ever since.<ref name=hvo-hist-loa>{{cite web|title=Mauna Loa|url=https://hvo.wr.usgs.gov/observatory/hvo_history_mloa.html|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|author=Russell A. Apple}}</ref>

Eruptions on Mauna Loa are almost always preceded and accompanied by prolonged episodes of seismic activity, the monitoring of which was the primary and often only warning mechanism in the past and which remains viable today. [[Seismograph|Seismic stations]] have been maintained on Hawaiʻi since the Observatory's inception, but these were concentrated primarily on Kīlauea, with coverage on Mauna Loa improving only slowly through the 20th century.<ref name=hvo-seismic>{{cite web|title=HVO Seismic Network|url=https://hvo.wr.usgs.gov/earthquakes/history/|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|date=June 18, 2001}}</ref> Following the invention of modern monitoring equipment, the backbone of the present-day monitoring system was installed on the volcano in the 1970s. Mauna Loa's July 1975 eruption was forewarned by more than a year of seismic unrest, with the HVO issuing warnings to the general public from late 1974; the 1984 eruption was similarly preceded by as much as three years of unusually high seismic activity, with [[volcanologist]]s predicting an eruption within two years in 1983.<ref name=hov-monitoring_data>{{cite web|title=Long-term Monitoring Data|url=https://hvo.wr.usgs.gov/maunaloa/current/monitoringdata.php|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|archive-date=February 17, 2013|archive-url=https://web.archive.org/web/20130217012832/http://hvo.wr.usgs.gov/maunaloa/current/monitoringdata.php}}</ref>

The modern monitoring system on Mauna Loa consists not only of its local seismic network but also of a large number of [[GPS]] stations, [[tiltmeter]]s, and [[strainmeter]]s that have been anchored on the volcano to monitor [[Deformation (volcanology)|ground deformation]] due to swelling of Mauna Loa's subterranean [[magma chamber]], which presents a more complete picture of the events proceeding eruptive activity. The GPS network is the most durable and wide-ranging of the three systems, while the tiltmeters provide the most sensitive predictive data, but are prone to erroneous results unrelated to actual ground deformation; nonetheless a survey line across the caldera measured a {{convert|76|mm|in|0|abbr=on}} increase in its width over the year preceding the 1975 eruption, and a similar increase in 1984 eruption. Strainmeters, by contrast, are relatively rare.<ref name=hvo-monitoring_current>{{cite web|title=Mauna Loa Volcano, Hawaiʻi: Current Monitoring|url=https://hvo.wr.usgs.gov/maunaloa/current/currentmonitoring.php|publisher=Hawaiian Volcano Observatory – United States Geological Survey|access-date=January 26, 2013|archive-date=February 17, 2013|archive-url=https://web.archive.org/web/20130217005623/http://hvo.wr.usgs.gov/maunaloa/current/currentmonitoring.php}}</ref> The Observatory also maintains two [[gas detector]]s at Mokuʻāweoweo, Mauna Loa's summit caldera, as well as a publicly accessible [https://hvo.wr.usgs.gov/cams/panorama.php?cam=MLcam live webcam] and occasional screenings by [[interferometric synthetic aperture radar]] imaging.<ref name=hov-monitoring_data/>

==Human history==
===Pre-contact===
The first [[Ancient Hawaiian]]s to arrive on Hawaii island lived along the shores where food and water were plentiful.<ref name="nasa-outrigger">{{cite web|title=Final Environmental Statement for the Outrigger Telescopes Project: Volume II|url=http://planetquest.jpl.nasa.gov/Outrigger/finalDocuments/fullDocument/OTP-FEIS-Volume-II.pdf|archive-url=https://web.archive.org/web/20090421000952/http://planetquest.jpl.nasa.gov/Outrigger/finalDocuments/fullDocument/OTP-FEIS-Volume-II.pdf|archive-date=April 21, 2009|publisher=[[NASA]]|access-date=September 4, 2012|page=C–9|date=February 2005}}</ref> Flightless birds that had previously known no predators became a staple food source.<ref name="haw-culture">{{cite web|title=Culture: The First Arrivals: Native Hawaiian Uses |url=http://www.hawaii.edu/maunakea/5_culture.pdf |work=Mauna Kea Mountain Reserve Master Plan |publisher=[[University of Hawaii]] |access-date=September 2, 2012 |archive-url=https://web.archive.org/web/20121011113028/http://www.hawaii.edu/maunakea/5_culture.pdf |archive-date=October 11, 2012}}</ref> Early settlements had a major impact on the local ecosystem, and caused many extinctions, particularly amongst bird species, as well as introducing foreign plants and animals and increasing erosion rates.<ref name="ps-1982">{{cite journal|last=Kirch|first=Patrick V.|title=The Impact of the Prehistoric Polynesians on the Hawaiian Ecosystem|journal=[[Pacific Science]]|date=January 1982|volume=36|issue=1|pages=1–14|url=http://scholarspace.manoa.hawaii.edu/handle/10125/406|access-date=September 2, 2012|publisher=[[University of Hawaiʻi  Press]]|hdl=10125/406}}</ref> The prevailing lowland forest ecosystem was transformed from forest to grassland; some of this change was caused by the use of fire, but the main reason appears to have been the introduction of the [[Rattus exulans|Polynesian rat]] (''Rattus exulans'').<ref>{{cite journal|last=Athens|first=Stephen|author2=Tuggle, H. David|author3=Ward, Jerome V.|author4=Welch, David J.|year=2002|title=Avifaunal Extinctions, Vegetation Change and Polynesian Impacts in Prehistoric Hawaiʻi|journal=Archaeology in Oceania|volume=37|url=https://www.questia.com/googleScholar.qst;jsessionid=C6A3E763540A70D4D8429AF57BF5D92C.inst1_1a?docId=5002488775|access-date=September 4, 2012|issue=2|page=57|doi=10.1002/j.1834-4453.2002.tb00507.x|archive-date=June 5, 2012|archive-url=https://archive.today/20120605041612/http://www.questia.com/googleScholar.qst;jsessionid=C6A3E763540A70D4D8429AF57BF5D92C.inst1_1a?docId=5002488775|url-access=subscription}}</ref>

Ancient Hawaiian [[Hawaiian religion|religious practice]] holds that the five volcanic peaks of the island are sacred, and regards Mauna Loa, the largest of them all, with great admiration;<ref>{{cite web|title=Information on the Mauna Loa Volcano in Hawaii|url=http://traveltips.usatoday.com/information-mauna-loa-volcano-hawaii-13725.html|work=[[USA Today]]|access-date=January 27, 2013|author=Caitlin Kelly}}</ref> but what mythology survives today consists mainly of oral accounts from the 18th century first compiled in the 19th. Most of these stories agree that the Hawaiian [[Volcano deity|volcano goddess]], [[Pele (deity)|Pele]], resides in [[Halemaʻumaʻu]] on Kilauea; however a few place her home at Mauna Loa's summit caldera Mokuʻāweoweo, and the mythos in general associates her with all volcanic activity on the island.<ref>{{cite web |author=Ken Hon |author-link=Ken Hon |title=Hawaiian Oral History related to Geology |url=http://www.uhh.hawaii.edu/~kenhon/GEOL205/Legends/default.htm |access-date=January 27, 2013 |publisher=[[University of Hawaii at Hilo]]}}</ref> Regardless, Kīlauea's lack of a geographic outline and strong volcanic link to Mauna Loa led to it being considered an offshoot of Mauna Loa by the Ancient Hawaiians, meaning much of the mythos now associated with Kīlauea was originally directed at Mauna Loa proper as well.<ref name="USGS-dw">{{Cite book|year=1987 |title=Volcanism in Hawaii: papers to commemorate the 75th anniversary of the founding of the Hawaii Volcano Observatory |editor=R. W. Decker |publisher=United States Geological Survey |volume=1 |series=United States Geological Survey Professional Paper, 1350 |url=https://pubs.usgs.gov/pp/1987/1350/pp1350_vol1.pdf |access-date=September 2, 2012 |display-editors=etal |archive-url=https://web.archive.org/web/20121010062038/http://pubs.usgs.gov/pp/1987/1350/pp1350_vol1.pdf |archive-date=October 10, 2012}}</ref>{{rp|154–155}}

Ancient Hawaiians constructed an extensive trail system on Hawaiʻi island, today known as the [[Ala Kahakai National Historic Trail]]. The network consisted of short trailheads servicing local areas along the main roads and more extensive networks within and around agricultural centers. The positioning of the trails was practical, connecting living areas to farms and ports, and regions to resources, with a few upland sections reserved for gathering and most lines marked well enough to remain identifiable long after regular use had ended. One of these trails, the [[Ainapo Trail]], ascended from the village of Kapāpala over {{convert|3400|m|ft|0|abbr=on}} in about {{convert|56|km|mi|0|abbr=on}} and ended at Mokuʻāweoweo at Mauna Loa's summit. Although the journey was arduous and required several days and many porters, ancient Hawaiians likely made the journey during eruptions to leave offerings and prayers to honor Pele, much as they did at Halemaʻumaʻu, neighboring Kilauea's more active and more easily accessible caldera. Several camps established along the way supplied water and food for travelers.<ref name=nrhpinv2>{{cite web|title=National Register Of Historic Places Inventory – Nomination Form for Federal Properties – Ainapo Trail|url=https://npgallery.nps.gov/pdfhost/docs/NRHP/Text/74000290.pdf|author=Russell A. Apple|publisher=[[National Park Service]]|access-date=January 27, 2013|date=August 20, 1974|url-status=live|archive-url=https://web.archive.org/web/20120929071811/http://pdfhost.focus.nps.gov/docs/NRHP/Text/74000290.pdf|archive-date=September 29, 2012}}</ref><ref name=nature-2005>{{cite web|title=The Proposed Mauka Trails System: The Roles and History of Trails on the Big Island|url={{NRHP url|id=74000290}}|publisher=[[The Nature Conservancy]]|access-date=January 27, 2013|author=Rick Warshauer|date=October 2005}}</ref>

=== European summiting attempts ===
[[James Cook]]'s [[third voyage of James Cook|third voyage]] was the first to make landfall on Hawaiʻi island, in 1778, and following adventures along the North American west coast, Cook returned to the island in 1779. On his second visit [[John Ledyard]], a [[corporal]] of the [[Royal Marines]] aboard {{HMS|Resolution|1771|6}}, proposed and received approval for an expedition to the summit Mauna Loa to learn "about that part of the island, particularly the peak, the tip of which is generally covered with snow, and had excited great curiosity." Using a compass, Ledyard and small group of ships' mates and native attendants attempted to make a direct course for the summit. However, on the second day of traveling the route became steeper, rougher, and blocked by "impenetrable thickets," and the group was forced to abandon their attempt and return to [[Kealakekua Bay]], reckoning they had "penetrated 24 miles and we suppose [were] within 11 miles of the peak"; in reality, Mokuʻāweoweo lies only {{convert|32|km|mi|0|abbr=on}} east of the bay, a severe overestimation on Ledyard's part. Another of Cook's men, [[Lieutenant]] [[James King (Royal Navy officer)|James King]], estimated the peak to be at least {{convert|5600|m|ft|0|abbr=on}} high based on its [[snow line]].<ref name="earliest">{{cite journal|url=http://evols.library.manoa.hawaii.edu/bitstream/handle/10524/599/JL25059.pdf?sequence=2|title=Earliest Ascents of Mauna Loa Volcano, Hawaiʻi |publisher=Hawaiian Historical Society, Honolulu |author=Walther M. Barnard |hdl= 10524/599 |journal=Hawaiian Journal of History|volume=25 |year=1991}}</ref><ref name="measuring">{{cite journal|url=http://evols.library.manoa.hawaii.edu/bitstream/handle/10524/359/JL25077.pdf?sequence=2|title=Measuring the Mountain: the United States Exploring Expedition on Mauna Loa, 1840–1841 |publisher=Hawaiian Historical Society |author=Roberta A. Sprague |hdl=10524/359 |journal=Hawaiian Journal of History |volume=25 |year=1991}}</ref>

[[File:Archibald Menzies 1754-1842.jpg|thumb|The Scottish botanist and naturalist [[Archibald Menzies]] was the first European to reach the summit of Mauna Loa, on his third attempt.]]
The next attempt to summit Mauna Loa was an expedition led by [[Archibald Menzies]], a botanist and naturalist on the 1793 [[Vancouver Expedition]]. In February of that year Menzies, two ships' mates, and a small group of native Hawaiian attendants attempted a direct course for the summit from [[Kealakekua Bay]], making it {{convert|26|km|mi|0|abbr=on}} inland by their reckoning (an overestimation) before they were turned away by the thickness of the forest. On a second visit by the expedition to the island in January of the next year Menzies was placed in charge of exploring the island interior, and after traversing the flanks of [[Hualālai]] he and his party arrived at the high plateau separating the two volcanoes. Menzies decided to make a second attempt (above the objections of the accompanying island chief), but again his progress was arrested by unassailable thickets.<ref name="earliest"/>

Menzies made a third attempt to summit Mauna Loa in February 1794. This time the botanist consulted King [[Kamehameha I]] for advice and learned that he could take canoes to the south and follow the ʻAinapō Trail, not knowing of its existence beforehand. Significantly better prepared, Menzies, Lieutenant [[Joseph Baker (Royal Navy officer)|Joseph Baker]] and Midshipman George McKenzie of ''Discovery'', and a servant (most likely Jonathan Ewins, listed on the ship's muster as "Botanist's L't") reached the summit, which Menzies estimated to be {{convert|4156|m|ft|0|abbr=on}} high with the aid of a [[barometer]] (consistent with a modern value of {{convert|4169|m|ft|0|abbr=on|disp=comma}}). He was surprised to find heavy snow and morning temperatures of {{convert|-3|C|F|0|abbr=on}}, and was unable to compare the heights of Mauna Loa and Kea but correctly supposed the latter to be taller based on its larger snow cap.<ref name="earliest"/> The feat of summitting Mauna Loa was not to be repeated for forty years.<ref name="earliest"/>

The Hawaiian Islands were the site of fervent missionary work, with the first group of missionaries arrived at [[Honolulu]] in 1820 and the second in 1823. Some of these missionaries left for Hawaiʻi island, and spent ten weeks traveling around it, preaching at local villages and climbing Kilauea, from which one of its members, [[William Ellis (British missionary)|William Ellis]], observed Mauna Loa with the aid of a telescope and ascertained it and Kea to be "perhaps 15,000 to 16,000 feet above the level of the sea"; they did not, however, attempt to climb the volcano itself. It is sometimes reported that the missionary Joseph Goodrich reached the summit around this time, but he never claimed this himself, though he did summit Mauna Kea and describe Mokuʻāweoweo with the aid of another telescope.<ref name="measuring"/>

The next successful ascent was made on January 29, 1834, by the Scottish botanist [[David Douglas (botanist)|David Douglas]], who also reached the summit caldera using the ʻAinapō Trail. By the time Douglas reached the summit the environment had put him under extreme duress, but he nonetheless stayed overnight to make measurements of the summit caldera's proportions and record barometric data on its height, both now known to be wildly inaccurate. Douglas collected biological samples on the way both up and down, and after a difficult and distressing descent began collating his samples; he planned to return to England, but instead several months later his body was discovered mysteriously crushed in a pit beside a dead wild boar<ref name="measuring"/>

Isidor Löwenstern successfully climbed Mauna Loa in February 1839, only the third successful climb in 60&nbsp;years.<ref name="earliest"/>

===Wilkes expedition===
[[File:Wilkes campsite.jpg|thumb|upright=1.5|Sketch of Wilkes' campsite by ship's artist [[Alfred Thomas Agate]]]]

The [[United States Exploring Expedition]] led by Lieutenant [[Charles Wilkes]] was tasked with a vast survey of the Pacific Ocean starting in 1838.<ref>{{cite book| title=Narrative of the United States Exploring Expedition |author=Charles Wilkes |year=1849 |volume=IV |pages=111–162| url=https://books.google.com/books?id=lbMNAAAAQAAJ| publisher=G. P. Putnam}}</ref> In September 1840 they arrived in [[Honolulu]], where repairs to the ships took longer than expected. Wilkes decided to spend the winter in Hawaii and take the opportunity to explore its volcanoes while waiting for better weather to continue the expedition. King [[Kamehameha III]] assigned American medical missionary Dr. [[Gerrit P. Judd]] to the expedition as a translator.<ref name="measuring"/>

Wilkes sailed to [[Hilo]] on the [[Hawaii (island)|island of Hawaiʻi]] and decided to climb Mauna Loa first, since it looked easier than [[Mauna Kea]]. On December 14 he hired about 200 porters, but after he left he realized only about half the equipment had been taken, so he had to hire more Hawaiians at higher pay. When they reached Kīlauea after two days, their guide Puhano headed off to the established ʻAinapō Trail. Wilkes did not want to head back downhill so he blazed his own way through dense forest directed by a compass. The Hawaiians were offended by the waste of sacred trees which did not help morale. At about {{convert|6000|ft|m}} elevation they established a camp called "Sunday Station" at the edge of the forest.

Two guides joined them at Sunday Station: Keaweehu, "the bird-catcher" and another whose Hawaiian name is not recorded, called "ragsdale". Although Wilkes thought he was almost to the summit, the guides knew they were less than halfway up. Since there was no water at Sunday Station, porters had to be sent back ten miles (16&nbsp;km) to a [[lava tube]] on ʻAinapō Trail which had a known supply. After an entire day replenishing stocks, they continued up to a second camp they called "Recruiting Station" at about {{convert|9000|ft|m}} elevation. After another full day's hike they established "Flag Station" on December 22, and by this time were on the ʻAinapō Trail. Most of the porters were sent back down to get another load.

At the Flag Station Wilkes and his eight remaining men built a circular wall of lava rocks and covered the shelter with a canvas tent. A snowstorm was in progress and several suffered from [[altitude sickness]]. That night (December 23), the snow on the canvas roof caused it to collapse. At daylight some of the group went down the trail to retrieve firewood and the gear abandoned on the trail the day before. After another day's climb, nine men reached the rim of Mokuʻāweoweo. They could not find a way down its steep sides so chose a smooth place on the rim for the camp site, at coordinates {{coord|19|27|59|N|155|34|54|W| type:landmark_region:US-HI| display=inline}}. Their tent was pitched within {{convert|60|ft|m}} of the crater's edge, secured by lava blocks.<ref name="focus">{{cite web| author=Russell A. Apple
|url={{NRHP url|id=74000295}} | title=Wilkes Campsite Nomination form | work=National Register of Historic Places | publisher=National Park Service |year=1973}}</ref>

The next morning they were unable to start a fire using friction due to the thin air at that altitude, and sent for matches. By this time, the naval officers and Hawaiians could not agree on terms to continue hiring porters, so sailors and marines were ordered from the ships. Dr. Judd traveled between the summit and the Recruiting Station to tend the many who suffered from altitude sickness or had worn out their shoes on the rough rock. Christmas Day was spent building rock walls around the camp to give some protection from the high winds and blowing snow. It took another week to bring all the equipment to the summit, including a [[pendulum]] designed for measuring slight variations in gravity.<ref name="focus"/>
[[File:Moku-A-Weo-Weo.jpg|thumb|right|Sketch of Mokuʻāweoweo from Wilkes' journal]]

On December 31, 1840, the pre-fabricated pendulum house was assembled. Axes and chisels cut away the rock surface for the pendulum's base. It took another three days to adjust the clock to the point where the experiments could begin. However, the high winds made so much noise that the ticks could often not be heard, and varied the temperature to make measurements inaccurate. Grass had to be painstakingly brought from the lowest elevations for insulation to get accurate measurements.

On Monday, January 11, Wilkes hiked around the summit crater. Using an optical method, he estimated Mauna Kea was {{convert|193|ft|m}} higher, while modern measurements indicate a difference of about {{convert|125|ft|m}}.<ref name=maunakea/> On January 13, 1841, he had "Pendulum Peak, January 1841 U.S. Ex, Ex." cut into a rock at the site.
The tents were dismantled and Hawaiians carried the gear down over the next three days, while Wilkes enjoyed a [[lomilomi massage]]. He continued his measurements at lower elevations and left the island on March 5. For all the effort he did not obtain any significant results, attributing gravity discrepancies to "the tides".<ref name="measuring"/>

The Wilkes expedition's camp site's ruins are the only known physical evidence in the Pacific of the U.S. Exploring Expedition.<ref name="focus"/> The camp site was listed on the [[National Register of Historic Places]] on July 24, 1974, as site 74000295,<ref name="nris">{{NRISref|2009a}}</ref> and is state historic site 10-52-5507.<ref>[http://hawaii.gov/dlnr/hpd/register/reghaw.pdf Historic Places in Hawaii County] on official state web site</ref>

===Today===
A summit shelter was built with some of the stones from Wilkes' camp site and mortar in 1934. In 1916 Mokuʻāweoweo was included in [[Hawaii Volcanoes National Park]], and a new trail was built directly from park headquarters at Kīlauea, an even more direct route than the one taken by Wilkes.<ref name="nrhpinv2"/> This trail, arriving at the summit from the east via Red Hill, became the preferred route due to its easier access and gentler slope. The historic [[Ainapo Trail|ʻAinapō Trail]] fell into disuse, and was reopened in the 1990s. A third modern route to the summit is from the [[Saddle Road]] up to the [[Mauna Loa Observatory]] which is at {{convert|11135|ft|m}} elevation a few miles north of Mokuʻāweoweo and the North Pit trail.<ref>{{cite web| url=http://www.mlo.noaa.gov |title=NOAA Mauna Loa Observatory |publisher=[[National Oceanic and Atmospheric Administration]] web site |access-date=July 4, 2009}}</ref>

==Climate==
[[File:Monthly Climate Normals (1991-2020) - MAUNA LOA 5 NNE,HI.svg|thumb|right|Climate chart for Mauna Loa]]
[[Trade wind]]s blow from east to west across the Hawaiian islands, and the presence of Mauna Loa strongly affects the local climate. At low elevations, the eastern (windward) side of the volcano receives heavy rain; [[Hilo]] is the wettest city in Hawaii and the fourth-wettest city in the United States, behind the [[southeast Alaska]]n cities of [[Whittier, Alaska|Whittier]], [[Ketchikan, Alaska|Ketchikan]] and [[Yakutat, Alaska|Yakutat]]. The rainfall supports extensive [[forest]]ation. The western (leeward) side has a much drier climate. At higher elevations, the amount of precipitation decreases, and skies are very often clear. Very low temperatures mean that precipitation often occurs in the form of snow, and the summit of Mauna Loa is described as a ''[[periglacial]]'' region, where freezing and thawing play a significant role in shaping the landscape.<ref>{{cite web|url=http://www.soest.hawaii.edu/GG/HCV/mloa-flora.html|title=Mauna Loa Flora and Climate|publisher=Hawaii Center for Volcanology|year=2004|access-date=July 28, 2007|last=Rubin|first=Ken|author2=Minicola, Rochelle}}</ref>

Mauna Loa has a [[tropical climate]] with warm temperatures at lower elevations and cool to cold temperatures higher up year-round. Below is the table for the slope observatory, which is at {{convert|11150|ft|m}} in the [[alpine climate|alpine zone]]. The highest recorded temperature was {{convert|78|F|C}} and the lowest was {{convert|18|F|C}} on September 26, 1990, and February 20, 1962, respectively.<ref name= NOAA>{{cite web |url = https://www.weather.gov/wrh/Climate?wfo=hfo |title = NowData – NOAA Online Weather Data |publisher = National Oceanic and Atmospheric Administration |access-date = September 13, 2021}}</ref>

{{Weather box
|collapsed=
|single line= Y
|location= Mauna Loa 5 NNE (1991–2020 normals, extremes 2005–present)
|temperature colour= 
|Jan record high F= 66
|Feb record high F= 66
|Mar record high F= 66
|Apr record high F= 67
|May record high F= 67
|Jun record high F= 68
|Jul record high F= 69
|Aug record high F= 68
|Sep record high F= 67
|Oct record high F= 66
|Nov record high F= 64
|Dec record high F= 63
|Jan avg record high F = 60.1
|Feb avg record high F = 58.1
|Mar avg record high F = 58.5
|Apr avg record high F = 61.0
|May avg record high F = 63.7
|Jun avg record high F = 64.7
|Jul avg record high F = 65.3
|Aug avg record high F = 64.8
|Sep avg record high F = 62.8
|Oct avg record high F = 62.9
|Nov avg record high F = 59.4
|Dec avg record high F = 58.6
|year avg record high F = 66.6
|Jan high F= 51.1
|Feb high F= 50.1
|Mar high F= 50.5
|Apr high F= 53.1
|May high F= 55.5
|Jun high F= 57.6
|Jul high F= 57.5
|Aug high F= 57.3
|Sep high F= 56.5
|Oct high F= 55.8
|Nov high F= 52.4
|Dec high F= 51.1
|year high F= 54.0
|Jan mean F = 43.2
|Feb mean F = 42.2
|Mar mean F = 42.7
|Apr mean F = 44.8
|May mean F = 47.4
|Jun mean F = 49.3
|Jul mean F = 49.1
|Aug mean F = 49.0
|Sep mean F = 48.6
|Oct mean F = 47.7
|Nov mean F = 44.8
|Dec mean F = 43.4
|year mean F = 46.0
|Jan low F= 35.4
|Feb low F= 34.3
|Mar low F= 34.8
|Apr low F= 36.5
|May low F= 39.3
|Jun low F= 41.1
|Jul low F= 40.7
|Aug low F= 40.7
|Sep low F= 40.6
|Oct low F= 39.6
|Nov low F= 37.2
|Dec low F= 35.8
|year low F= 38.0
|Jan avg record low F = 28.1
|Feb avg record low F = 27.7
|Mar avg record low F = 29.7
|Apr avg record low F = 31.3
|May avg record low F = 32.7
|Jun avg record low F = 35.4
|Jul avg record low F = 35.2
|Aug avg record low F = 35.6
|Sep avg record low F = 35.9
|Oct avg record low F = 34.8
|Nov avg record low F = 31.4
|Dec avg record low F = 30.5
|year avg record low F = 25.7
|Jan record low F= 22
|Feb record low F= 21
|Mar record low F= 27
|Apr record low F= 28
|May record low F= 31
|Jun record low F= 31
|Jul record low F= 30
|Aug record low F= 31
|Sep record low F= 33
|Oct record low F= 32
|Nov record low F= 29
|Dec record low F= 26
|year record low F= 21
|precipitation colour = green
|Jan precipitation inch = 1.10
|Feb precipitation inch = 1.04
|Mar precipitation inch = 1.94
|Apr precipitation inch = 0.87
|May precipitation inch = 0.60
|Jun precipitation inch = 0.43
|Jul precipitation inch = 1.27
|Aug precipitation inch = 2.38
|Sep precipitation inch = 0.67
|Oct precipitation inch = 1.47
|Nov precipitation inch = 1.21
|Dec precipitation inch = 1.32
|year precipitation inch = 14.30
|unit precipitation days = 0.01 inch
|Jan precipitation days = 3.9
|Feb precipitation days = 5.7
|Mar precipitation days = 6.8
|Apr precipitation days = 4.1
|May precipitation days = 4.1
|Jun precipitation days = 2.1
|Jul precipitation days = 3.7
|Aug precipitation days = 6.0
|Sep precipitation days = 4.8
|Oct precipitation days = 4.9
|Nov precipitation days = 4.6
|Dec precipitation days = 5.6
|year precipitation days = 56.3
|source 1 = NOAA<ref name= NOAA/><ref>
{{cite web
|url = https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly-1991-2020&stations=USW00021514&format=pdf&dataTypes=MLY-TMAX-NORMAL,MLY-TMIN-NORMAL,MLY-TAVG-NORMAL,MLY-PRCP-NORMAL,MLY-SNOW-NORMAL
|title = U.S. Climate Normals Quick Access – Station: N POLE, AK US USC00506581
|access-date = June 10, 2023
|archive-url = https://web.archive.org/web/20230610053050/https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly-1991-2020&stations=USW00021514&format=pdf&dataTypes=MLY-TMAX-NORMAL,MLY-TMIN-NORMAL,MLY-TAVG-NORMAL,MLY-PRCP-NORMAL,MLY-SNOW-NORMAL
|archive-date = 2023-06-10
}}
</ref>}}

{{Weather box
|location = Mauna Loa slope observatory 3,400 meters (11,150 feet) (1981–2010 normals, extremes 1955–present)
|single line = Y
|temperature colour=
|Jan record high F = 67
|Feb record high F = 69
|Mar record high F = 66
|Apr record high F = 67
|May record high F = 68
|Jun record high F = 71
|Jul record high F = 70
|Aug record high F = 69
|Sep record high F = 78
|Oct record high F = 68
|Nov record high F = 65
|Dec record high F = 67
|year record high F = 78
|Jan avg record high F = 59.7
|Feb avg record high F = 59.2
|Mar avg record high F = 59.3
|Apr avg record high F = 61.0
|May avg record high F = 62.5
|Jun avg record high F = 64.9
|Jul avg record high F = 65.0
|Aug avg record high F = 64.9
|Sep avg record high F = 64.1
|Oct avg record high F = 62.2
|Nov avg record high F = 60.2
|Dec avg record high F = 59.6
|year avg record high F = 67.2
|Jan high F = 51.9
|Feb high F = 51.2
|Mar high F = 51.9
|Apr high F = 53.2
|May high F = 55.8
|Jun high F = 58.5
|Jul high F = 57.5
|Aug high F = 57.9
|Sep high F = 56.7
|Oct high F = 55.7
|Nov high F = 53.2
|Dec high F = 52.0
|year high F = 54.6
|Jan mean F = 43.6
|Feb mean F = 42.4
|Mar mean F = 43.1
|Apr mean F = 44.3
|May mean F = 47.1
|Jun mean F = 49.3
|Jul mean F = 48.6
|Aug mean F = 49.1
|Sep mean F = 48.1
|Oct mean F = 47.3
|Nov mean F = 46.1
|Dec mean F = 44.1
|year mean F = 46.1
|Jan low F = 35.3
|Feb low F = 33.7
|Mar low F = 34.2
|Apr low F = 35.3
|May low F = 38.4
|Jun low F = 40.2
|Jul low F = 39.6
|Aug low F = 40.2
|Sep low F = 39.4
|Oct low F = 38.8
|Nov low F = 38.9
|Dec low F = 36.2
|year low F = 37.5
|Jan avg record low F = 28.1
|Feb avg record low F = 27.3
|Mar avg record low F = 28.5
|Apr avg record low F = 29.8
|May avg record low F = 32.6
|Jun avg record low F = 34.6
|Jul avg record low F = 34.4
|Aug avg record low F = 35.4
|Sep avg record low F = 34.3
|Oct avg record low F = 33.7
|Nov avg record low F = 32.0
|Dec avg record low F = 28.7
|year avg record low F = 25.4
|Jan record low F = 19
|Feb record low F = 18
|Mar record low F = 20
|Apr record low F = 23
|May record low F = 27
|Jun record low F = 28
|Jul record low F = 26
|Aug record low F = 28
|Sep record low F = 29
|Oct record low F = 27
|Nov record low F = 25
|Dec record low F = 21
|year record low F = 18
|precipitation colour=green
|Jan precipitation inch = 2.48
|Feb precipitation inch = 1.51
|Mar precipitation inch = 1.75
|Apr precipitation inch = 1.33
|May precipitation inch = 1.00
|Jun precipitation inch = 0.51
|Jul precipitation inch = 1.16
|Aug precipitation inch = 1.50
|Sep precipitation inch = 1.36
|Oct precipitation inch = 1.16
|Nov precipitation inch = 1.78
|Dec precipitation inch = 2.01
|year precipitation inch = 17.55
|unit precipitation days = 0.01 in
|Jan precipitation days = 4
|Feb precipitation days = 5
|Mar precipitation days = 6
|Apr precipitation days = 5
|May precipitation days = 4
|Jun precipitation days = 3
|Jul precipitation days = 4
|Aug precipitation days = 5
|Sep precipitation days = 5
|Oct precipitation days = 5
|Nov precipitation days = 5
|Dec precipitation days = 4
|year precipitation days = 55
|Jan snow inch = 0.0
|Feb snow inch = 1.0
|Mar snow inch = 0.3
|Apr snow inch = 1.3
|May snow inch = 0.0
|Jun snow inch = 0.0
|Jul snow inch = 0.0
|Aug snow inch = 0.0
|Sep snow inch = 0.0
|Oct snow inch = 0.0
|Nov snow inch = 0.0
|Dec snow inch = 1.0
|year snow inch = 3.7
|source 1 = [[NOAA]]<ref name= NOAA/><ref name=NCEI>
{{cite web
|url = https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly&startDate=0001-01-01&endDate=9996-12-31&stations=USC00516198&format=pdf
|title = Station: Mauna Loa Slope OBS 39, Hawaii
|work = U.S. Monthly Climate Normals (1981–2010)
|publisher = National Oceanic and Atmospheric Administration
|access-date = September 13, 2021
|archive-url = https://web.archive.org/web/20211203224150/https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly&startDate=0001-01-01&endDate=9996-12-31&stations=USC00516198&format=pdf
|archive-date = 2021-12-03}}</ref>
|source 2 = Western Climate Center (precipitation and snow 1955–2005)<ref>{{cite web|work=MAUNA LOA SLOPE OBS, HAWAII|title=Period of Record Monthly Climate Summary|url=http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?himaun|publisher=NOAA|access-date=September 13, 2021}}</ref>}}
{{Graph:Weather monthly history
| table=ncei.noaa.gov/weather/Mauna Loa.tab
| title=Mauna Loa monthly weather statistics}}

==Observatories==
[[File:Mauna Loa CO2 monthly mean concentration.svg|thumbnail|right|Atmospheric [[carbon dioxide|CO<sub>2</sub>]] concentrations measured at the [[Mauna Loa Observatory]].]]
The location of Mauna Loa has made it an important location for atmospheric monitoring by the [[Global Atmosphere Watch]] and other scientific observations. The [[Mauna Loa Solar Observatory]] (MLSO), located at {{convert|11155|ft|m|0}} on the northern slope of the mountain, has long been prominent in observations of the Sun. The [[NOAA]] [[Mauna Loa Observatory]] (MLO) is located close by. From its location well above local human-generated influences, the MLO monitors the global atmosphere, including the [[greenhouse gas]] [[carbon dioxide]]. Measurements are adjusted to account for local [[outgassing]] of CO<sub>2</sub> from the volcano.<ref>Rhodes, J.M. and Lockwood, J. P. (editors), (1995) ''Mauna Loa Revealed: Structure, Composition, History, and Hazards'', Washington D.C., American Geophysical Union Monograph 92, p. 95</ref>

The [[Yuan-Tseh Lee Array for Microwave Background Anisotropy]] (AMiBA) sits at an elevation of {{convert|11155|ft|m|0|sp=us}}. It was established in October 2006 by the [[Academia Sinica Institute of Astronomy and Astrophysics]] (ASIAA) to examine [[cosmic microwave background radiation]].<ref>{{cite web|url=http://www.asiaa.sinica.edu.tw/project/amiba.php|title=The Yuan Tseh Lee Array for Microwave Background Anisotropy (AMiBA)|publisher=[[ASIAA]]|date=May 12, 2012|access-date=July 26, 2013|archive-date=July 29, 2013|archive-url=https://web.archive.org/web/20130729005355/http://www.asiaa.sinica.edu.tw/project/amiba.php}}</ref>

==See also==
*[[HI-SEAS]]
*[[List of mountain peaks of the United States]]
**[[List of volcanoes of the United States]]
***[[List of mountain peaks of Hawaii]]
*[[List of Ultras of Oceania]]
*[[List of Ultras of the United States]]
*[[Olympus Mons]] – The tallest volcano in the Solar System
* [[Olaa Forest]] on Mauna Loa, in the [[Hawaiʻi Volcanoes National Park]]

==Notes==
{{notelist}}

==References==
{{reflist}}

==External links==
{{Commons and category|Mauna Loa}}
*[https://www.usgs.gov/volcanoes/mauna-loa Mauna Loa – United States Geological Survey]
*[http://www.soest.hawaii.edu/GG/HCV/maunaloa.html Hawaii Center for Volcanology]
*[http://www.volcano.si.edu/world/volcano.cfm?vnum=1302-02= Global Volcanism Program entry]
*[https://gml.noaa.gov/obop/mlo/ Mauna Loa Observatory (MLO) – NOAA]
*[https://www2.hao.ucar.edu/mlso/mlso-home-page Mauna Loa Solar Observatory (MLSO)]

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[[Category:Mauna Loa| ]]
[[Category:Volcanoes of the Island of Hawaii]]
[[Category:Active volcanoes]]
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[[Category:Hawaiʻi Volcanoes National Park]]
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[[Category:Calderas of Hawaii]]
[[Category:Hawaiian words and phrases]]
[[Category:National Register of Historic Places in Hawaiʻi Volcanoes National Park]]
[[Category:Extreme points of the United States]]
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[[Category:Polygenetic shield volcanoes]]
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[[Category:Pleistocene Oceania]]
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[[Category:Cenozoic Hawaii]]
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[[Category:Ultra-prominent peaks of Oceania]]