View source for Cerro Azul (Chile volcano)

{{Short description|Mountain in Curicó Province, Chile}}
{{About|the volcano in Chile|the volcano in Ecuador|Cerro Azul (Ecuador volcano)}}

{{Infobox mountain
| name = Cerro Azul
| photo = Cerro Azul.jpg
| photo_alt = 
| photo_caption = Aerial view of Cerro Azul from the west.
| elevation_m = 3788
| elevation_ref = <ref name=GVP/><ref name=usgs_Chile>{{cite web|url=http://vulcan.wr.usgs.gov/Volcanoes/Chile/description_chile_volcanoes.html|title=Chile Volcanoes and Volcanics|publisher=[[United States Geological Survey]]|access-date=October 12, 2020|archive-url=https://web.archive.org/web/20130220121704/http://vulcan.wr.usgs.gov/Volcanoes/Chile/description_chile_volcanoes.html|archive-date=2013-02-20}}</ref>
| prominence_m =
| prominence_ref=
| listing = [[List of volcanoes in Chile]]
| range = [[Andes]]
| location = [[Chile]]
| map = Chile
| map_alt = Cerro Azul is located in East-central Chile, which lies on the southwestern coast of South America.
| map_caption = Chile and adjacent lands, showing the location of Cerro Azul
| map_size = 200
| label_position = right
| coordinates   = {{coord|35.653|S|70.761|W|type:mountain_scale:100000|format=dms|display=inline,title}}
| coordinates_ref = <ref name=GVP/>
| type = [[Stratovolcano]]
| age = [[Quaternary]]
| volcanic_arc/belt = [[South Volcanic Zone]]
| last_eruption = August 1967<ref name=GVP/>
}}
'''Cerro Azul''' ({{IPA|es|ˈsero aˈsul}}, ''blue hill'' in [[Spanish language|Spanish]]), sometimes referred to as '''Quizapu''', is an active [[stratovolcano]] in the [[Maule Region]] of central [[Chile]], immediately south of [[Descabezado Grande]]. Part of the [[Andean Volcanic Belt|South Volcanic Zone]] of the [[Andes]], its summit is {{convert|3788|m|ft|0|sp=us}} above [[sea level]], and is capped by a summit crater that is {{convert|500|m|sp=us}} wide and opens to the north. Beneath the summit, the volcano features numerous [[scoria]] [[Volcanic cone#Cinder cone|cone]]s and flank vents.

Cerro Azul is responsible for several of South America's largest recorded eruptions, in 1846 and 1932. In 1846, an [[effusive eruption]] formed the vent at the site of present-day [[#Quizapu Crater|Quizapu crater]] on the northern flank of Cerro Azul and sent lava flowing down the sides of the volcano, creating a [[lava field]] 8–9 square kilometres (3–3.5 square miles) in area. [[Phreatic]] and [[Strombolian]] volcanism between 1907 and 1932 excavated this crater. In 1932, one of the largest explosive eruptions of the 20th&nbsp;century occurred at Quizapu Crater and sent {{convert|9.5|km3|sp=us}} of ash into the atmosphere. The volcano's most recent eruption was in 1967.

The South Volcanic Zone has a long history of eruptions and poses a threat to the surrounding region. Any [[volcanic hazard]]—ranging from minor ashfalls to [[pyroclastic flow]]s—could pose a significant risk to humans and wildlife. Despite its inactivity, Cerro Azul could again produce a major eruption; if this were to happen, relief efforts would probably be quickly organized. Teams such as the [[Volcano Disaster Assistance Program]] (VDAP) are prepared to effectively evacuate, assist, and rescue people threatened by volcanic eruptions.

== Geography and geology ==

=== Regional setting ===
[[Andean Volcanic Belt|Volcanism in the Chilean Andes]] is caused by [[subduction]] of the [[Nazca Plate|Nazca]] and [[Antarctic Plate|Antarctic]] [[tectonic plate]]s under the [[South American Plate]]. Volcanoes in Chile occur in the [[Central Volcanic Zone|Central]] (CVZ), [[South Volcanic Zone|South]] (SVZ), and [[Austral Volcanic Zone|Austral]] Volcanic Zones (AVZ). The gap that separates the Central and South Volcanic Zones is caused by shallow-angle subduction in the [[Pampean flat-slab segment]] where the more buoyant [[Juan Fernández Ridge]] subducts under the South American continent.<ref name="JF ridge">{{cite journal|doi=10.1016/S0895-9811(02)00004-4|title=The Challenger Juan Fernández Maipo major tectonic transition of the Nazca Andean subduction system at 33 34°S: geodynamic evidence and implications|year=2002|last1=Yáñez|first1=G|journal=Journal of South American Earth Sciences|volume=15|issue=1|pages=23–38|bibcode = 2002JSAES..15...23Y |hdl=10533/173277|hdl-access=free}}</ref><ref name=Stern>Stern et al., p. 147.</ref> This buoyant region prevents the [[Slab (geology)|slab]] (subducting tectonic plate) from diving deep into the [[mantle (geology)|mantle]],<ref name="JF ridge"/> where the heat and pressure would destabilize the mineral [[Chlorite group|chlorite]], releasing water that would in turn cause [[flux melting|melting]] and [[volcanism]].<ref name="chlorite">{{cite journal|doi=10.1038/nature08044|title=Kinematic variables and water transport control the formation and location of arc volcanoes|year=2009|last1=Grove|first1=T. L.|last2=Till|first2=C. B.|last3=Lev|first3=E.|last4=Chatterjee|first4=N.|last5=Médard|first5=E.|journal=Nature|volume=459|pages=694–7|pmid=19494913|issue=7247|bibcode = 2009Natur.459..694G |s2cid=4379126}}</ref> The [[Patagonian Volcanic Gap]], which separates the South and Austral Volcanic Zones, is caused by the subduction of the [[Chile Ridge]],<ref>{{cite journal|last1=Russo|first1=R.M.|last2=Vandecar|first2=John C.|last3=Comte|first3=Diana|last4=Mocanu|first4=Victor I.|last5=Gallego|first5=Alejandro|last6=Murdie|first6=Ruth E.|title=Subduction of the Chile Ridge: Upper mantle structure and flow|journal=GSA Today|pages=4–10|year=2010|doi=10.1130/GSATG61A.1}}</ref> though it is less clear whether this gap also is due to [[flat-slab subduction]]; it may instead arise because melting of the subducting slab there produced [[felsic]] [[igneous rock]]s instead of volcanoes.<ref>{{cite journal|doi=10.1016/j.tecto.2004.12.016|title=Seismic ridge subduction and topography: Foreland deformation in the Patagonian Andes|year=2005|last1=Ramos|first1=V.|author-link=Víctor Alberto Ramos|journal=Tectonophysics|volume=399|issue=1–4|pages=73–86|bibcode = 2005Tectp.399...73R |hdl=11336/92808|hdl-access=free}}</ref>

Offshore volcanism also occurs in Chile. Intraplate volcanism generated from the [[Easter hotspot|Easter]] and [[Juan Fernández hotspot]]s has formed many Chilean islands, including [[Isla Salas y Gómez]], [[Easter Island]], and the [[Juan Fernández Islands]]. Underwater volcanism occurs due to [[seafloor spreading]] along the Chile Ridge.<ref name=Stern/>

Nearly 100 [[Quaternary]] ([[Pleistocene]]- or [[Holocene]]-age) independent volcanoes exist in the country, in addition to 60&nbsp;volcanic complexes and [[caldera]] systems.<ref name=Stern/> Of the 200 historically active volcanoes in the Andean Range, 36 are found in Chile.<ref name=SouthAmerica>{{cite web|url=http://vulcan.wr.usgs.gov/Volcanoes/SouthAmerica/description_south_america_volcanoes.html|title=South America Volcanoes|publisher=[[United States Geological Survey]]|date=February 28, 2002|access-date=May 9, 2009}}</ref>

=== Local setting ===
[[File:Descabezado Grande y Cerro Azul.jpg|thumb|right|alt=|The mountain with the appearance of a truncated cone, at the centre of the image, is [[Descabezado Grande]] volcano, and close to it is the pyramidal Cerro Azul.]]

Cerro Azul is part of the South Volcanic Zone, which runs through central and western Chile and extends south to Argentina. This range includes at least nine [[volcanic field|caldera complexes]], more than 70&nbsp;of Chile's stratovolcanoes and volcanic fields that have been active in the Quaternary, and hundreds of minor eruptive centres. The South Volcanic Zone is the most volcanically active region in Chile, and produces around one eruption per year. Its largest historical eruption was at Quizapu Crater, located on the north side of Cerro Azul's summit (see below), and its most active volcanoes are [[Llaima]] and [[Villarrica (volcano)|Villarrica]].<ref name=Stern156>Stern et al., pp. 154–156.</ref>

Cerro Azul, just {{convert|7|km|mi|sp=us}} south of [[Descabezado Grande]] volcano, is part of the Descabezado Grande–Cerro Azul eruptive system,<ref name=GVP>{{cite gvp|vn=357060|title=Cerro Azul|access-date=May 9, 2009}}</ref> a volcanic field that comprises its two large namesake volcanic edifices and several smaller vents,<ref name=Casitas>{{cite journal|title=Composite Chemostratigraphy of Lavas From the Casitas Shield, Descabezado Grande-Cerro Azul Volcanic Complex, Chilean Andes|author=Wulff, Andrew H.|bibcode=2003AGUFM.V32H..07W|journal=American Geophysical Union, Fall Meeting|year=2003|volume=32|pages=V32H–07}}</ref> including 12 Holocene calderas.<ref name=Hildreth96/> Both volcanoes lie on top of the Casitas Shield, a plateau built of over 100 [[lava flow]]s that erupted in at least 12&nbsp;volcanic episodes during the Quaternary period. The upper lava layers are dated at 340,000&nbsp;years.<ref name=Casitas/><ref name=Hildreth96/>

As with the majority of the Andean volcanoes, Cerro Azul is a [[stratovolcano]], meaning that it consists of layers, or [[stratum|strata]], of [[volcanic ash]] and [[lava flows]].<ref>{{cite web |url=http://pubs.usgs.gov/gip/volc/types.html |title=Principal Types of Volcanoes |publisher=United States Geological Survey |access-date=April 2, 2009}}</ref> The cone of Cerro Azul has a total volume of about {{convert|11|km3|cumi|0|sp=us}}, and is a young feature, formed in the Holocene.<ref name=Hildreth96/> It is made of agglutinated [[pyroclast]]s and some [[dacite]]–[[andesine]] lavas.<ref name=Hildreth96>Hildreth and Drake 1992, p.96</ref> The cone has a few volcanic craters;<ref name="GVP"/> the majority of its eruptions in [[recorded history]] have originated from Quizapu Crater on the northern flank of Cerro Azul's cone.<ref name=Hildreth96/> Other craters lying on the flanks of the main cone are Caracol ("Snail"), Crater los Quillayes, Crater la Resolana, and Crater sin Nombre ("Nameless Crater"). All of the craters lie between {{convert|2000|and|3000|m|sp=us}} in elevation, except Quizapu, which is {{convert|3292|m|sp=us}} up the volcano.<ref name="GVP"/> The summit of Cerro Azul is crowned by an asymmetric crater about {{convert|500|m|ft|0|sp=us}} in diameter.<ref name=Hildreth96/> Pleistocene glacial activity is evident in the form of 500&nbsp;meter (1,640&nbsp;ft) deep struts in the volcanoes' sides. These deep cuts have revealed strata of older rock.<ref name=Hildreth96/>

[[Image:Map chile volcanoes.gif|thumb|right|alt=Five major volcanoes range from Cerro Azul in central Chile, south through Copahue, Llaima, and Villarrica, to Cerro Hudson.|Major Chilean volcanoes are marked by red triangles on this map.]]

=== Quizapu Crater ===
Quizapu, which formed during the 1846 eruption, is the most prominent crater.<ref name=Hildreth/> It is also known as Cerro del Medio ("Middle Hill") or Volcan Nuevo ("New Volcano").<ref name="GVP"/> The volcanic vent formed during an effusive eruption involving [[hornblende]]–dacite flows accompanied by [[tephra]], and the crater was excavated by [[phreatic eruption|phreatic]] and [[Strombolian eruption|Strombolian]] eruptions between 1907 and 1932. Pent-up pressure within the volcano spawned an enormous [[Plinian eruption]] in 1932. The volume of lava ejected during this single event is roughly equal to that ejected during the rest of the eruptive history at Quizapu, since its formation in 1846. Although {{convert|9.5|km3|sp=us}} of material was ejected, no [[subsidence]] was detected from the removal of magma.<ref name=Hildreth>Hildreth and Drake, pp.96–98</ref> Because of [[drag (physics)|aerodynamic drag]], a Plinian eruption excavates a circular crater. As the earlier eruptions had already formed an approximately circular caldera<!--was this a caldera or a crater?-->, the Plinian eruption was able to proceed efficiently, with minimal drag and minimal reshaping of the crater.<ref name=Hildreth108>Hildreth and Drake, p. 108.</ref>

The Quizapu Crater is almost perfectly circular, and rises to a prominence of {{convert|150|to|250|m|ft|-1|sp=us}} above the surrounding portions of the volcano.<ref name=Hildreth/> Cresting at {{convert|3292|m|ft|0|sp=us}} in elevation,<ref name="GVP"/> Quizapu is one of the highest known Plinian craters. The radius of the crater floor, which is the current inner vent, is around {{convert|150|m|ft|-2|sp=us}}, while the radius of its rim is {{convert|300|-|350|m|ft|-1|sp=us}}. The crater floor lies at {{convert|2928|m|ft|0|sp=us}}, and the rim lies {{convert|150|-|300|m|ft|-2|sp=us}} above that, giving the walls an average slope of 34–35 degrees (close to the [[angle of repose]]). The western wall is cut by two long, dacitic lava flows: probably the remnants of a [[lava dome|dome]] or an eruption.<ref name=Hildreth/> The crater is surrounded by debris from its 1932 eruption, and topped by layers—{{convert|50|m|ft|-1|sp=us}} thick—of mafic [[scoria]] and ash.<ref name=Hildreth103>Hildreth and Drake, p. 103.</ref>

== Climate and vegetation ==
Cerro Azul is situated in a [[Mediterranean climate]] zone, characterized by hot and dry summers but mild and wet winters. The temperatures and [[Precipitation (meteorology)|precipitation]] are strongly dependent on topography. In the Andes the annual average maximum temperatures lie in the range {{convert|20|to|25|C|F}}, while minimum temperatures are below {{convert|0|C|F}}. Annual precipitation is up to 800&nbsp;mm (31.5&nbsp;inches).<ref name=Flora>{{cite web|publisher=[[Smithsonian Institution]]|title=Mediterranean region and la Campana national Park, Central Chile|url=http://botany.si.edu/projects/cpd/sa/sa44.htm|access-date=February 28, 2010|url-status=dead|archive-url=https://web.archive.org/web/20091008133920/http://botany.si.edu/projects/cpd/sa/sa44.htm|archive-date=October 8, 2009}}</ref>

Vegetation in the Andes varies with elevation. Above 1,600&nbsp;meters (5,249&nbsp;ft) the slopes of mountains are covered by [[Alpine climate|Alpine]]-like [[steppe]], while below there are zones of ''[[Nothofagus]]'' forest, ''Hygrophilous'' forest, [[Mediterranean forests, woodlands, and scrub|''Sclerophylous'' forest]], and [[matorral]]. The number of plant species is likely to exceed 2,000, although no comprehensive study of the flora of Central Chile has been undertaken.<ref name=Flora/>

== Eruptive history ==
Cerro Azul has a history of eruptions dating back to at least 1846. The known events include effusive eruptions (lava flows), which created the Quizapu vent, [[explosive eruption]]s, and phreatic eruptions. [[Pyroclastic flow]]s have also been observed as a result of some of these explosive eruptions. The earliest recorded eruption began on November 26, 1846, while the volcano's last eruption began on August 9, 1967.<ref name="GVP"/> The volcano has produced two of the largest eruptions in South America in recorded history, in 1846 and 1932. Both released {{convert|4|-|5|km3|mi3|1|sp=us}} of the dacitic magma.<ref name=Hildreth96/>

=== First record of activity, 1846 ===
On November 26, 1846, Cerro Azul erupted. This was the first report of activity at the volcano, and no trace of [[fumarole]]s, adjacent vents, or pre-eruptive activity exists. Most descriptions of the eruption come from the backcountry herdsmen ([[arriero]]s). One, who was camped in a valley approximately {{convert|7|km|mi|0|sp=us}} east of Quizapu, heard "a great noise and a cloud of ash" emanate from the mountain in the late afternoon. No precursor activity was reported, and the herdsman claimed that there were no earthquakes during the late afternoon eruption.<ref name=Hildreth96/>

That night, two herdsmen near the site heard a continuous roar, punctuated by loud bangs and crackling sounds "like that of great rockslides". Lightning and thunder accompanied the spectacle. They saw many blue flames, and were choked by [[sulfur|sulfurous gas]]. Observers in [[Talca, Chile|Talca]] {{convert|85|km|mi|0|sp=us}} away heard the eruption noises, and the sulfurous odors reached them the day after the eruption. None of the reports mention earthquakes or ash fall, though the crackling and banging sounds could be from [[block lava]]s ({{okina}}a{{okina}}ā).<ref name="Hildreth9798">Hildreth and Drake, pp. 97–98.</ref>

This first recorded eruption of Cerro Azul was effusive, and formed the volcanic vent at Quizapu. Hornblende–dacite lava erupted with small masses of tephra, which had been [[degassing|degassed]] shortly before the eruption.<ref name=Hildreth/> Lava flowed over the [[Estero Barroso Valley]] and westward into the [[Río Blanquillo Valley]].<ref name="GVP"/> By November 28, the volcano appeared at rest, and the herdsman returned to the place of first observation. There, they found a blocky lava field. The lava was still hot, fuming and crackling with gas and flame. Fascinated by the volcano, [[Ignacy Domeyko]] traveled to Chile to study the field and found its width to be {{convert|8|-|9|km2|sqmi|sp=us}}. By 1992 the field had grown to twice that size.<ref name=Hildreth98>Hildreth and Drake, p. 98.</ref>

=== Early 20th century ===
Cerro Azul was quiet from 1846 to the beginning of the 20th century. After a possible precursor explosive event in 1903, Cerro Azul once again erupted in 1907. Between 1907 and 1914, plumes and clouds of ash frequently rose out of the caldera, and at least a few of these events were explosive. On September 8, 1914, an explosive eruption sent a [[Eruption column|plume]] 6 or 7 kilometers (about 4&nbsp;mi) into the air over 8&nbsp;minutes. By 1916, these eruptions had produced a caldera nearly identical to the one in existence today.<ref name=Hildreth98/>

The volcano also erupted phreatically several times, as recorded by Vogel in 1913 and 1920, with its activity increasing from 1916 to 1926. During these years, the eruptions grew more frequent and more violent. A major outburst on November 2, 1927 started a period of nearly continuous violent eruptions that lasted until 1929. During this period, Cerro Azul sometimes erupted daily, sending columns of ash as far as 6 or 7 kilometers (about 4&nbsp;mi) into the air. Quizapu Crater grew slightly during this eruptive period.<ref name=Hildreth98/>

Pre-1932 volcanism was largely phreatic or fumarolic, as evidenced by the lack of tephra generated by these eruptions. Photographs from 1912 show vapor plumes containing little ash, rising {{convert|1|-|2|km|mi|1|sp=us}} above the crater.<ref name=Hildreth98/>

=== Major eruption, 1932 ===
{{Infobox eruption
 | name = 1932 eruption of Cerro Azul
 | image = 
 | image_size =
 | caption = 
 | start_date = {{start date|1932|04|10}}<ref name=Hildreth99/>
 | start_time =
 | end_date = {{end date|1932|04|21}}<ref name="GVP"/>
 | volcano = 
 | type = [[Plinian eruption|Plinian]]
 | location = 
 | coordinates = 
 | VEI = 5<ref name="GVP"/>
 | map =
 | map_size=
 | map_caption =
 | impact = 
}}

By 1932, Quizapu had produced many phreatic events and one effusive eruption, but no large Plinian eruptions. This frequency of minor eruptive activity proved to be a precursor for a major eruption. On 25 January 1932, observers in [[Malargue]] saw a large black cloud over the summit. By 9 April, the volcano emitted green gas and started to "bellow like a bull".<ref name=Hildreth99>Hildreth and Drake, p. 99.</ref> On April 10, Cerro Azul finally erupted, releasing a towering column or plume of white gas. After 10 AM, the plume turned black with ash and began to form an umbrella shape. The ash was carried by wind into [[Puesto El Tristan]] in Argentina, about {{convert|47|km|mi|0|sp=us}} away, where beginning at 1 PM it rained down for hours. At 4 PM, coarser sandy material and some [[pumice]] [[lapilli]] began to fall.<ref name=Hildreth99/>

Cerro Azul's April 1932 eruption was one of the largest of the 20th century. Releasing {{convert|9.5|km3|cumi|0|sp=us}} of lava, the volcano ejected primarily dacitic tephra,<ref name="GVP"/> accompanied by [[rhyodacite]], [[andesite]],<ref>{{cite journal|title=U-series crystal ages in historic eruptions of Volcan Quizapu, Chile|author1=Ruprecht, P.|author2=Cooper, K.M.|author3=Bergantz, G.W.|bibcode=2005AGUFM.V13B0529R|journal=American Geophysical Union, Fall Meeting|year=2005|volume=13|pages=0529}}</ref> and minuscule amounts of andesitic and [[basalt]]ic scoria. At least one eruptive period lasted for 18&nbsp;hours, creating an "exceptionally uniform" deposit.<ref name=Hildreth/> Eruption columns, extending {{convert|27|-|30|km|mi|sp=us}} into the air, were sighted. [[Phenocrysts]] were similar to the effusive eruption in 1846.<ref name=Hildreth/> Soon after, both the [[Tinguiririca (volcano)|Tinguiririca]] and Descabezado Grande volcanoes began erupting, sending clouds of ash {{convert|800|km|mi|-1|sp=us}} into Argentina.<ref>{{cite magazine|title=Irrepressible Andes|magazine=[[Time (magazine)|Time]]|date=18 April 1932|url=https://content.time.com/time/magazine/0,9263,7601320418,00.html|access-date=October 12, 2020}}</ref> The eruption had a [[Volcanic Explosivity Index]] (VEI) of at least 5.<ref name="GVP"/>

Since the eruption of 1932 Quizapu has been quiet. In 1949 and 1967 small ash clouds were reported, while in the 1980s there were no signs of activity other than fumaroles.<ref name=Hildreth101>Hildreth and Drake, p. 101.</ref>

== Threats and preparedness ==
Cerro Azul is in the South Volcanic Zone, where many volcanoes pose a threat to human life. Among the other active volcanoes of the South Volcanic Zone are [[Mount Hudson]], Llaima, and Villarrica.<ref name=usgs_Chile/> Villarrica and Llaima together have more than 80 reported episodes of volcanism since 1558, and at least 40 South Volcanic Zone volcanoes have had Holocene-age eruptions.<ref name=Stern154>Stern et al., p.154.</ref>

Every known type of eruption ([[Hawaiian eruption|Hawaiian]], Strombolian, Plinian, [[Subplinian eruption|subplinian]], phreatic, [[Phreatomagmatic eruption|phreatomagmatic]], and [[Vulcanian eruption|Vulcanian]]) has occurred at some point in the range.<ref name=Stern156/> Cerro Azul itself has experienced phreatic, Strombolian, and Plinian activity in human history.<ref name="Hildreth"/> The type of eruption tends to correspond with lava composition. Strombolian eruptions at Llaima, Antuco, Villarrica, and elsewhere have been produced by basaltic to basaltic–andesitic activity. Dacitic to [[rhyolite|rhyolitic]] lavas have been linked to subplinian and Plinian eruptions, such as those at Quizapu (1932) and Hudson (1991). Because of this variability, volcanic hazards from Cerro Azul and the surrounding region could come in many different forms. Historical eruptions typically have produced lahars, lava flows, and ashfalls. Lava flows and [[lahar]]s could wipe out entire cities or towns. Ashfall produced by explosive eruptions could interfere with air traffic. Most threatening of all is the risk of pyroclastic flows or avalanches, which have historically traversed as far as {{convert|100|km|mi|0|sp=us}} in the region.<ref name=Stern156/>

[[File:Cerro hudson.jpg|thumb|right|alt=Glaciers around a black caldera from which steam is rising|Mount Hudson, an active volcano in the SVZ, shortly after an eruption in 1991. The volcano has produced eruptions as powerful as [[Volcanic Explosivity Index]] degree six.<ref>{{cite web|url=https://volcano.si.edu/volcano.cfm?vn=358057&vtab=Eruptions|title=Cerro Hudson » Eruptive History|publisher=Global Volcanism Program, Smithsonian Institution|access-date=October 12, 2020}}</ref>]]

Past eruptions of Quizapu Crater ejected enormous amounts of ash that traveled as far as Brazil. After the 1932 eruption, the local vegetation was devastated, and the area remained barren until the 1990s, though human life was not impacted.<ref name=Stern101>Stern et al., p.101.</ref> Despite the extent of its eruptions, the threat to humans from Quizapu is relatively small because of the remote location of Cerro Azul. Nevertheless, the size of past eruptions is large enough for scientists to be worried. Evidence of a potentially deadly threat lies in a lahar at Descabezado Grande.<ref name=Hildreth99/> Historically, lahars have killed thousands in the Andes.<ref name="nevado del ruiz">{{Cite web|url=http://volcanoes.usgs.gov/hazards/lahar/ruiz.php|title=Deadly Lahars from Nevado del Ruiz, Colombia: November 13, 1985|publisher=[[United States Geological Survey]]|date=September 30, 1999|access-date=March 18, 2010|archive-date=May 27, 2010|archive-url=https://web.archive.org/web/20100527195111/http://volcanoes.usgs.gov/hazards/lahar/ruiz.php|url-status=dead}}</ref><ref name="Tilling_Andean_Volcanoes">{{cite journal|last=Tilling|first=R.I.|year=2009|title=Volcanism and associated hazards: the Andean perspective|journal=Advances in Geosciences|publisher=[[European Geosciences Union]]|volume=22|pages=125–137|doi=10.5194/adgeo-22-125-2009|doi-access=free|bibcode=2009AdG....22..125T}}</ref> There is, however, a possibility that a large reservoir of rhyodacite magma may exist under the Azul–Descabezado complex. If this is the case, all previous eruptions in 1846–1967 were only preliminary, preclimactic leaks from the large magma chamber beneath, and a large caldera-forming eruption may be expected in the future.<ref name=Hildreth122>Hildreth and Drake, pp. 122–123.</ref>

If Cerro Azul were to erupt, relief efforts could be orchestrated. The Volcanic Disaster Assistance Program (VDAP) formed in response to the [[Armero tragedy|famous 1985 eruption]] of [[Nevado del Ruiz]] in [[Colombia]],<ref name=vdap_info>{{cite web|url=https://volcanoes.usgs.gov/projects/VDAP/about.html|title=VDAP Brings Nations Together in Volcanic Crisis Management and Response|work=Volcanic Disaster Assistance Program|publisher=United States Geological Survey|access-date=October 12, 2020}}</ref> and responded to the 1991 eruption of Mount Hudson in Chile.<ref name=VDAP/> The team's stated aim is to "reduce eruption-caused fatalities and economic losses in developing countries". Made up of various USGS offices (such as the [[Cascades Volcano Observatory]]; CVO that are responsible for monitoring [[Mount St. Helens]]), the team is outfitted with equipment capable of monitoring any volcano. This equipment allows them to predict volcanic eruptions effectively and rapidly, and to evacuate nearby homes.<ref name=VDAP>{{cite web|url=http://vulcan.wr.usgs.gov/Vdap/description_vdap.html|title=The USGS/OFDA Volcano Disaster Assistance Program |publisher=[[United States Geological Survey]]|date=March 21, 2001|access-date=February 25, 2010}}</ref>

== See also ==
{{portal|Mountains}}
*[[Geology of Chile]]
*[[List of volcanoes in Chile]]

== References ==
{{Reflist|30em}}

== Bibliography ==
* {{cite journal|title=Volcán Quizapu, Chilean Andes|bibcode=1992BVol...54...93H|author1=Hildreth, Wes|author2=Drake, Robert E.|journal=[[Bulletin of Volcanology]]|volume=54|issue=2|pages=93–125|year=1992|doi=10.1007/BF00278002|s2cid=128972435|url=https://zenodo.org/record/1232403}} [[Isopach map]]ping of the volcanic deposits, between {{convert|5|and|1|cm|in|1|sp=us}}, contradict 1930 estimates by about half.
* {{cite book | last1 = Stern | first1 = Charles R. | last2 = Moreno | first2 = Hugo|author-link2=Hugo Moreno Roa | last3 = López-Escobar | first3 = Leopoldo | last4 = Clavero | first4 = Jorge E. | last5 = Lara | first5 = Luis E. | last6 = Naranjo | first6 = José A. | last7 = Parada | first7 = Miguel A. | last8 = Skewes | first8 = M. Alexandra | author-link3 = Leopoldo López Escobar | chapter = 5. Chilean Volcanoes | editor = Moreno, Teresa |editor2=Gibbons, Wes | title = Geology of Chile | location = London, United Kingdom | publisher = Geological Society of London | year = 2007 | isbn = 978-1-86239-219-9| pages=149–180 | chapter-url=https://books.google.com/books?id=h4DBQR9jDsoC&pg=PA147}}


== Further reading ==
* {{cite book | last = González-Ferrán | first = Óscar | title = Volcanes de Chile
   | publisher = Santiago, Chile: Instituto Geográfico Militar | year = 1995 | isbn =956-202-054-1 | page=640 pp }} <small>(in Spanish; also includes volcanoes of Argentina, Bolivia, and Peru)</small>
{{Andean volcanoes}}
{{featured article}}

{{DEFAULTSORT:Azul}}
[[Category:Active volcanoes]]
[[Category:Mountains of Chile]]
[[Category:South Volcanic Zone]]
[[Category:Stratovolcanoes of Chile]]
[[Category:Subduction volcanoes]]
[[Category:VEI-5 volcanoes]]
[[Category:Volcanoes of Maule Region]]
[[Category:20th-century volcanic events]]
[[Category:Three-thousanders of the Andes]]