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[[File:Desembocadura del Ebro.jpg|thumb|Aerial picture of the [[Ebro]] river as it reaches the [[Mediterranean Sea]] by the [[Ebro Delta]]]] | [[File:Desembocadura del Ebro.jpg|thumb|Aerial picture of the [[Ebro]] river as it reaches the [[Mediterranean Sea]] by the [[Ebro Delta]]]] | ||
In [[geology]] and [[geomorphology]] a '''base level''' is the lower limit for an [[erosion|erosion process]].<ref name=Goudie2004>{{cite encyclopedia|last=Goudie|first=A.S.|author-link=Andrew Goudie (geographer)|editor-last=Goudie|editor-first=A.S.|encyclopedia=Encyclopedia of Geomorphology|title=Base level|year=2004|page=62|publisher=Routledge}}</ref> The modern term was introduced by [[John Wesley Powell]] in 1875.<ref name=Goudie2004/> The term was subsequently appropriated by [[William Morris Davis]] who used it in his [[cycle of erosion]] theory.<ref name=Goudie2004/><ref name=Orme2007>{{cite journal |last1=Orme |first1=Anthony R. |date=2007 |title=The Rise and Fall of the Davisian Cycle of Erosion: Prelude, Fugue, Coda, and Sequel |journal=Physical Geography |volume=28 |issue=6 |pages=474–506 |doi= 10.2747/0272-3646.28.6.474|bibcode=2007PhGeo..28..474O |s2cid=128907423 }}</ref> The "ultimate base level" is the surface that results from projection of the [[sea level]] under landmasses.<ref name=Goudie2004/> It is to this base level that topography tends to approach due to erosion, eventually forming a [[peneplain]] close to the end of a cycle of erosion.<ref name="Phillips">Phillips, Jonathan D. (2002), [https://www.sciencedirect.com/science/article/pii/S0169555X01001568 "Erosion, isostatic response, and the missing peneplains"], ''[[Geomorphology (journal)|Geomorphology]]'', Vol. 45, No. 3-4. [http://www.elsevier.com/wps/find/homepage.cws_home Elsevier] {{Webarchive|url=https://web.archive.org/web/20100124190936/http://www.elsevier.com/wps/find/homepage.cws_home |date=2010-01-24 }}, 15 June 2002, pp. 225-241. {{doi|10.1016/S0169-555X(01)00156-8}}.</ref><ref>Chorley, R.J. (1973). ''The History and Study of Landforms or The Development of Geomorphology. Vol. Two: The Life and Work of William Morris Davis,'' Methuen.</ref><ref name=Greenetal2013>{{cite journal |last1=Green |first1=Paul F. |last2=Lidmar-Bergström |first2=Karna |last4=Bonow |first4=Johan M. |last3=Japsen |first3=Peter |last5=Chalmers |first5=James A. |author-link2=Karna Lidmar-Bergström |date=2013 |title=Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins |journal=[[Geological Survey of Denmark and Greenland|Geological Survey of Denmark and Greenland Bulletin]] |volume=30 |pages=18 |doi=10.34194/geusb.v30.4673 |doi-access=free }}</ref><ref name=Karnaetal2014>{{cite journal |last1=Lidmar-Bergström |first1=Karna |last2=Bonow |first2=Johan M. |last3=Japsen |first3=Peter |author-link=Karna Lidmar-Bergström|date=2013 |title=Stratigraphic Landscape Analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence |journal=[[Global and Planetary Change]] |volume=100 |pages=153–171 |doi= 10.1016/j.gloplacha.2012.10.015|bibcode=2013GPC...100..153L }}</ref> | In [[geology]] and [[geomorphology]] a '''base level''' is the lower limit for the [[vertical position]] of an [[erosion|erosion process]].<ref name=Goudie2004>{{cite encyclopedia|last=Goudie|first=A.S.|author-link=Andrew Goudie (geographer)|editor-last=Goudie|editor-first=A.S.|encyclopedia=Encyclopedia of Geomorphology|title=Base level|year=2004|page=62|publisher=Routledge}}</ref> The modern term was introduced by [[John Wesley Powell]] in 1875.<ref name=Goudie2004/> The term was subsequently appropriated by [[William Morris Davis]] who used it in his [[cycle of erosion]] theory.<ref name=Goudie2004/><ref name=Orme2007>{{cite journal |last1=Orme |first1=Anthony R. |date=2007 |title=The Rise and Fall of the Davisian Cycle of Erosion: Prelude, Fugue, Coda, and Sequel |journal=Physical Geography |volume=28 |issue=6 |pages=474–506 |doi= 10.2747/0272-3646.28.6.474|bibcode=2007PhGeo..28..474O |s2cid=128907423 }}</ref> The "ultimate base level" is the surface that results from horizontal projection of the [[sea level]] under landmasses (the [[geoid]]).<ref name=Goudie2004/> It is to this base level that [[topography]] tends to approach due to erosion, eventually forming a [[peneplain]] close to the end of a cycle of erosion.<ref name="Phillips">Phillips, Jonathan D. (2002), [https://www.sciencedirect.com/science/article/pii/S0169555X01001568 "Erosion, isostatic response, and the missing peneplains"], ''[[Geomorphology (journal)|Geomorphology]]'', Vol. 45, No. 3-4. [http://www.elsevier.com/wps/find/homepage.cws_home Elsevier] {{Webarchive|url=https://web.archive.org/web/20100124190936/http://www.elsevier.com/wps/find/homepage.cws_home |date=2010-01-24 }}, 15 June 2002, pp. 225-241. {{doi|10.1016/S0169-555X(01)00156-8}}.</ref><ref>Chorley, R.J. (1973). ''The History and Study of Landforms or The Development of Geomorphology. Vol. Two: The Life and Work of William Morris Davis,'' Methuen.</ref><ref name=Greenetal2013>{{cite journal |last1=Green |first1=Paul F. |last2=Lidmar-Bergström |first2=Karna |last4=Bonow |first4=Johan M. |last3=Japsen |first3=Peter |last5=Chalmers |first5=James A. |author-link2=Karna Lidmar-Bergström |date=2013 |title=Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins |journal=[[Geological Survey of Denmark and Greenland|Geological Survey of Denmark and Greenland Bulletin]] |volume=30 |pages=18 |doi=10.34194/geusb.v30.4673 |doi-access=free }}</ref><ref name=Karnaetal2014>{{cite journal |last1=Lidmar-Bergström |first1=Karna |last2=Bonow |first2=Johan M. |last3=Japsen |first3=Peter |author-link=Karna Lidmar-Bergström|date=2013 |title=Stratigraphic Landscape Analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence |journal=[[Global and Planetary Change]] |volume=100 |pages=153–171 |doi= 10.1016/j.gloplacha.2012.10.015|bibcode=2013GPC...100..153L }}</ref> | ||
There are also lesser [[structural geology|structural]] base levels where erosion is delayed by resistant rocks.<ref name=Goudie2004/> Examples of this include [[karst]] regions underlain by insoluble rock.<ref name=Ford2004>{{cite encyclopedia|last=Ford|first=Derek C.|editor-link=Andrew Goudie (geographer)|editor-last=Goudie|editor-first=A.S.|encyclopedia=Encyclopedia of Geomorphology|title=Cave |year=2004 |pages=124–128 |publisher=Routledge}}</ref> Base levels may be local when large landmasses are far from the sea or disconnected from it, as in the case of [[endorheic basin]]s.<ref name=Goudie2004/> An example of this is the [[Messinian salinity crisis]], in which the [[Mediterranean Sea]] dried up making the base level drop more than 1000 m below sea level.<ref>{{cite journal |last1=Fairbridge |first1=Rhodes W. |last2=Finkl Jr. |first2=Charles W.|author-link=Rhodes Fairbridge |date=1980 |title=Cratonic erosion unconformities and peneplains |journal=[[The Journal of Geology]] |volume=88 |issue=1 |pages=69–86 |doi= 10.1086/628474|bibcode=1980JG.....88...69F |s2cid=129231129 }}</ref><ref name=Goudie2005>{{cite journal |last1=Goudie |first1=A.S.|author-link=Andrew Goudie (geographer) |date=2005 |title=The drainage of Africa since the Cretaceous |journal=[[Geomorphology (journal)|Geomorphology]] |volume=67 |issue= 3–4|pages=437–456 |doi= 10.1016/j.geomorph.2004.11.008|bibcode=2005Geomo..67..437G}}</ref> | There are also lesser [[structural geology|structural]] base levels where erosion is delayed by resistant rocks.<ref name=Goudie2004/> Examples of this include [[karst]] regions underlain by insoluble rock.<ref name=Ford2004>{{cite encyclopedia|last=Ford|first=Derek C.|editor-link=Andrew Goudie (geographer)|editor-last=Goudie|editor-first=A.S.|encyclopedia=Encyclopedia of Geomorphology|title=Cave |year=2004 |pages=124–128 |publisher=Routledge}}</ref> Base levels may be local when large landmasses are far from the sea or disconnected from it, as in the case of [[endorheic basin]]s.<ref name=Goudie2004/> An example of this is the [[Messinian salinity crisis]], in which the [[Mediterranean Sea]] dried up making the base level drop more than 1000 m below sea level.<ref>{{cite journal |last1=Fairbridge |first1=Rhodes W. |last2=Finkl Jr. |first2=Charles W.|author-link=Rhodes Fairbridge |date=1980 |title=Cratonic erosion unconformities and peneplains |journal=[[The Journal of Geology]] |volume=88 |issue=1 |pages=69–86 |doi= 10.1086/628474|bibcode=1980JG.....88...69F |s2cid=129231129 }}</ref><ref name=Goudie2005>{{cite journal |last1=Goudie |first1=A.S.|author-link=Andrew Goudie (geographer) |date=2005 |title=The drainage of Africa since the Cretaceous |journal=[[Geomorphology (journal)|Geomorphology]] |volume=67 |issue= 3–4|pages=437–456 |doi= 10.1016/j.geomorph.2004.11.008|bibcode=2005Geomo..67..437G}}</ref> | ||
Latest revision as of 01:06, 2 June 2025
In geology and geomorphology a base level is the lower limit for the vertical position of an erosion process.[1] The modern term was introduced by John Wesley Powell in 1875.[1] The term was subsequently appropriated by William Morris Davis who used it in his cycle of erosion theory.[1][2] The "ultimate base level" is the surface that results from horizontal projection of the sea level under landmasses (the geoid).[1] It is to this base level that topography tends to approach due to erosion, eventually forming a peneplain close to the end of a cycle of erosion.[3][4][5][6]
There are also lesser structural base levels where erosion is delayed by resistant rocks.[1] Examples of this include karst regions underlain by insoluble rock.[7] Base levels may be local when large landmasses are far from the sea or disconnected from it, as in the case of endorheic basins.[1] An example of this is the Messinian salinity crisis, in which the Mediterranean Sea dried up making the base level drop more than 1000 m below sea level.[8][9]
The height of a base level also influences the position of deltas and river terraces.[1] Together with river discharge and sediment flux the position of the base level influences the gradient, width and bed conditions in rivers.[10] A relative drop in base level can trigger re-adjustments in river profiles including knickpoint migration and abandonment of terraces leaving them "hanging".[11] Base level fall is also known to result in progradation of deltas and river sediment at lakes or sea.[12] If the base level falls below the continental shelf, rivers may form a plain of braided rivers until headward erosion penetrates enough inland from the shelfbreak.[12]
When base levels are stable or rising rivers may aggrade.[12] Rising base levels may also drown the lower courses of rivers creating rias. This happened in the Nile during the Zanclean flood when its lower course became, in a relatively short time, a large estuary extending up to 900 km inland from the Mediterranean coast.[9]
Base level change may be related to the following factors:
- Sea level change[1]
- Tectonic movement[1]
- River capture[1]
- Extensive sedimentation[13]
References
es: Hoz (geografía) gl: Foz (xeografía)
- ↑ a b c d e f g h i j Script error: No such module "citation/CS1".
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- ↑ Phillips, Jonathan D. (2002), "Erosion, isostatic response, and the missing peneplains", Geomorphology, Vol. 45, No. 3-4. Elsevier Template:Webarchive, 15 June 2002, pp. 225-241. Script error: No such module "doi"..
- ↑ Chorley, R.J. (1973). The History and Study of Landforms or The Development of Geomorphology. Vol. Two: The Life and Work of William Morris Davis, Methuen.
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