{{short description|Collapse of a volcano}} [[File:18 mai 1980 - Éruption du Mont Saint-Hélène USA.jpg|thumb|Sector collapse during the 1980 eruption of Mount St. Helens<ref name=":0">{{Cite journal |last=Watt |first=Sebastian F. L. |date=2019-10-15 |title=The evolution of volcanic systems following sector collapse |url=https://www.sciencedirect.com/science/article/pii/S0377027318301604 |journal=Journal of Volcanology and Geothermal Research |language=en |volume=384 |pages=280–303 |doi=10.1016/j.jvolgeores.2019.05.012 |bibcode=2019JVGR..384..280W |s2cid=181821094 |issn=0377-0273|url-access=subscription }}</ref>|235x235px]] A '''sector collapse''' or '''lateral collapse''' is the structural failure and subsequent collapse of a minimum volume of {{cvt|1|km3}} of a volcano.<ref name=":0"/> Unlike smaller flank collapses, a sector collapse can involve the central volcanic pipe and historically this term had been restricted by some writers to such events in arc stratovolcanoes, but is now used for large events in any volcano.<ref name=":0"/> Sector collapses are one of the most hazardous volcanic events,<ref name=":1">{{Cite journal |last1=Kervyn |first1=M. |last2=Ernst |first2=G. G. J. |last3=Klaudius |first3=J. |last4=Keller |first4=J. |last5=Mbede |first5=E. |last6=Jacobs |first6=P. |date=2008-10-28 |title=Remote sensing study of sector collapses and debris avalanche deposits at Oldoinyo Lengai and Kerimasi volcanoes, Tanzania |journal=International Journal of Remote Sensing |language=en |volume=29 |issue=22 |pages=6565–6595 |bibcode=2008IJRS...29.6565K |doi=10.1080/01431160802168137 |issn=0143-1161 |s2cid=128817424}}</ref> often resulting in lateral blasts,<ref name=":0" /> landslides,<ref name=":2">{{Cite journal |last1=Romero |first1=Jorge E. |last2=Polacci |first2=Margherita |last3=Watt |first3=Sebastian |last4=Kitamura |first4=Shigeru |last5=Tormey |first5=Daniel |last6=Sielfeld |first6=Gerd |last7=Arzilli |first7=Fabio |last8=La Spina |first8=Giuseppe |last9=Franco |first9=Luis |last10=Burton |first10=Mike |last11=Polanco |first11=Edmundo |date=2021 |title=Volcanic Lateral Collapse Processes in Mafic Arc Edifices: A Review of Their Driving Processes, Types and Consequences |journal=Frontiers in Earth Science |volume=9 |page=325 |doi=10.3389/feart.2021.639825 |issn=2296-6463 |doi-access=free |bibcode=2021FrEaS...9..325R |hdl=11581/457992 |hdl-access=free }}</ref> and changes in volcanic eruptive behavior. Sector collapse can be caused by earthquakes,<ref name=":2" /> volcanic eruptions,<ref name=":0" /> gradual volcanic deformation,<ref name=":0" /> and other processes. Sector collapse events can occur on volcanoes at convergent and divergent plate boundaries.<ref name=":0" /> Sector collapses are generally very sudden; however, some attempts have been made to predict collapse events.
== Causes ==
=== Internal === [[File:Tata Sabaya evolution.jpg|thumb|Example of sector collapse: cross-section diagram of Tata Sabaya volcano (in Bolivia) (a) pre-collapse volcano, (b) after collapse, (c) new edifice built on top of collapsed old edifice|301x301px]] Sector collapse can result from internal volcanic processes. Volcanic eruption can damage originally stable magma chambers, causing a portion of the volcano to collapse.<ref name=":0" /> While eruption is one cause, sector collapse can occur without any eruption. Magmatic intrusions can also lead to sector collapse. Dikes fracture and deform rock, leaving the volcano weaker and more susceptible to collapse. Hydrothermal activity is another internal cause, likely due to reactions of acid-sulfates weakening volcanic rock. Gravity-induced collapse occurs when the volcanic slope approaches the critical angle of repose.<ref name=":2" /> The slope angle is a major factor in collapse events.<ref name=":1" />
=== External === Sector collapse sometimes occurs because of external processes. Seismic activity is a prominent cause of collapse events. Earthquakes can weaken the structural stability of volcanoes, leading to sudden collapse or contributing to a later collapse. Intense weather and heavy rainfall can cause damaging erosion, increasing likelihood of collapse.<ref name=":2" /> Glacial melting is another external cause of sector collapse, with the majority of glacial melt induced collapses occurring during the Pleistocene. Glacial melting increases volcanic slope and decreases pore pressure, leading to sector collapse.<ref name=":5">{{Cite journal |last=Tormey |first=Daniel |date=2010-11-01 |title=Managing the effects of accelerated glacial melting on volcanic collapse and debris flows: Planchon–Peteroa Volcano, Southern Andes |url=https://www.sciencedirect.com/science/article/pii/S0921818110001943 |journal=Global and Planetary Change |language=en |volume=74 |issue=2 |pages=82–90 |doi=10.1016/j.gloplacha.2010.08.003 |bibcode=2010GPC....74...82T |issn=0921-8181|url-access=subscription }}</ref> Sea level change has also been associated with sector collapse.<ref name=":2" />
=== Predicting sector collapse === Because sector collapse events occur suddenly and over small time periods, they are difficult to predict.<ref name=":0" /> More often, volcanoes are assessed for risk of sector collapse.<ref name=":5" /> Collapse ultimately occurs due to structural instability,<ref name=":0" /> which can be determined by volcanic slope angle, composition of the volcano, deformation, and other factors.<ref name=":2" />
== Consequences == [[File:After Effects (25727393810).jpg|thumb|Mudflow-induced property damage caused by the 1980 Mount St. Helens sector collapse]] [[File:Tata Sabaya debris avalanche DEM.jpg|thumb|Debris avalanche deposit of Tata Sabaya volcano's sector collapse]] === Changes to volcanic systems === Some volcanoes experience no changes in volcanic behavior while others experience altered rates of eruption and magma composition.<ref name=":0" /> Collapse is typically followed by phreatic eruption<ref name=":2" /> due to a reduction in magma chamber pressure after sector collapse. Damage caused by collapse can create a new and different volcanic plumbing system, which could impact eruption rates. Sector collapse often results in eruption of more mafic magma. Large overlying surface mass and the denser nature of mafic magma often prevents its rise. Collapse relieves some of the overlying surface mass thus allowing for more mafic magma composition.<ref name=":0" />
=== Human impacts === Sector collapses and landslides caused by them have directly resulted in more than 3,500 fatalities since 1600 and caused extensive property damage. A particularly deadly consequence of sector collapse is a tsunami. The Oshima-Oshima collapse led to a tsunami that killed 1,500 people. Sector collapse events can also displace thousands and cause homelessness.<ref name=":2" />
=== Identifying sector collapse === Prehistoric sector collapses are stored in the geological record<ref name=":0" /> in the form of debris avalanche deposits<ref name=":1" /> and collapse scars. Debris avalanche deposits are found typically up to {{cvt|20|km}} from the site of collapse,<ref name=":2" /> but in the case of the Hawaiian islands {{cvt|200|km}} away.<ref>{{cite book|chapter=Chapter 4 Instability of Hawaiian Volcanoes|first1=Roger P.|last1=Denlinger|first2=Julia K.|last2=Morgan|chapter-url=https://pubs.usgs.gov/pp/1801/downloads/pp1801_Chap4_Denlinger.pdf|title=Characteristics of Hawaiian Volcanoes Professional Paper 1801|editor-first1=Michael P.|editor-last1=Poland|editor-first2=Taeko Jane|editor-last2=Takahashi|editor-first3=Claire M.|editor-last3=Landowski|publisher=United States Geological Survey|year=2014|pages=149–176|isbn=9781411338722|archive-date=2017-08-10|access-date=2025-01-19|archive-url=https://web.archive.org/web/20170810145759/https://pubs.usgs.gov/pp/1801/downloads/pp1801_Chap4_Denlinger.pdf|url-status=bot: unknown}}{{rp|pp=156, 170}}</ref> Studying avalanche deposits informs on the time scale of the collapse and the volcano from which it originated.<ref name=":1" /> Collapse scars are also an indicator of sector collapse and are often described as "amphitheatre" or "horseshoe" shaped.<ref name=":2" /> One such collapse scar is the Sciara del Fuoco formed on the Stromboli volcano due to a sector collapse.<ref name=":3" />
== Examples == [[File:Mount Rainier Osceola collapse.png|thumb|Approximation of Mount Rainer's Osceola collapse ]]
=== Prehistoric ===
* Antuco<ref name=":0" /> * Chimborazo<ref name=":0" /> * Popocatépetl<ref>https://volcano.si.edu/volcano.cfm?vn=341090</ref> * Mount Rainier<ref>{{Cite web |title=Significant Lahars at Mount Rainier |url=https://www.usgs.gov/volcanoes/mount-rainier/science/significant-lahars-mount-rainier}}</ref> * Mount Shasta<ref>{{Cite web |title=Catastrophic Debris Avalanche at Mount Shasta |url=https://www.usgs.gov/volcanoes/mount-shasta/science/catastrophic-debris-avalanche-mount-shasta}}</ref> * Shiveluch<ref name=":0" /> * Stromboli<ref name=":3">{{Cite journal |last1=Kokelaar |first1=Peter |last2=Romagnoli |first2=Claudia |date=1995-08-01 |title=Sector collapse, sedimentation and clast population evolution at an active island-arc volcano: Stromboli, Italy |url=https://ui.adsabs.harvard.edu/abs/1995BVol...57..240K |journal=Bulletin of Volcanology |volume=57 |issue=4 |pages=240–262 |doi=10.1007/BF00265424 |bibcode=1995BVol...57..240K |s2cid=128687255 |issn=0258-8900}}</ref> [[File:Tankei - Eruption of Mount Bandai.jpg|thumb|Ukiyo-e depiction of 1888 Bandai Sector collapse by Japanese artist Inoue Tankei]]
=== Historic ===
* Anak Krakatoa, 2018<ref name=":0" /> * Mount Bandai, 1888<ref name=":0" /> * Bezymianny, 1956<ref name=":0" /> * Oshima-Oshima, 1741<ref name=":0" /> * Ritter Island, 1888: largest historical collapse<ref name=":0" /> * Mount St. Helens, 1980<ref name=":0" />
== See also == *Volcanology *Debris flow
== References == {{reflist}}
Category:Volcanoes Category:Geology terminology Category:Sector collapses