Lahar

The word lahar is of Javanese origin.{{Cite book|title= Encyclopedia of Volcanoes|chapter= Chapter 37 – Lahars and Their Deposits|doi= 10.1016/B978-0-12-385938-9.00037-7|publisher= Academic Press|date= 2015|location= Amsterdam|isbn= 978-0-12-385938-9|pages= 649–664|first1= James W.|last1= Vallance|first2= Richard M.|last2= Iverson|editor-first= Haraldur|editor-last= Sigurdsson}} Berend George Escher introduced it as a geological term in 1922.{{cite book|editor=Andrew S. Goudie|title=Encyclopedia of Geomorphology|volume=2|year=2004|chapter=Lahar|author=Vincent E. Neall|pages=597–599|publisher=Psychology Press |isbn=9780415327381|chapter-url=https://books.google.com/books?id=UHRU_6nUSR4C&pg=PA597}}

File:Sambisari 01.jpg Hindu temple near Yogyakarta in Java, Indonesia. The temple was buried 6.5 metres under the lahar volcanic debris accumulated from centuries of Mount Merapi eruptions.]]

The word lahar is a general term for a flowing mixture of water and pyroclastic debris. It does not refer to a particular rheology or sediment concentration.{{Citation|last1=Vallance|first1=James W.|title=Chapter 37 - Lahars and Their Deposits|date=2015-01-01|url=https://www.sciencedirect.com/science/article/pii/B9780123859389000377|encyclopedia=The Encyclopedia of Volcanoes (Second Edition)|pages=649–664|editor-last=Sigurdsson|editor-first=Haraldur|place=Amsterdam|publisher=Academic Press|language=en|isbn=978-0-12-385938-9|access-date=2021-03-26|last2=Iverson|first2=Richard M.}} Lahars can occur as normal stream flows (sediment concentration of less than 30%), hyper-concentrated stream flows (sediment concentration between 30 and 60%), or debris flows (sediment concentration exceeding 60%). Indeed, the rheology and subsequent behaviour of a lahar may vary in place and time within a single event, owing to changes in sediment supply and water supply. Lahars are described as 'primary' or 'syn-eruptive' if they occur simultaneously with or are triggered by primary volcanic activity. 'Secondary' or 'post-eruptive' lahars occur in the absence of primary volcanic activity, e.g. as a result of rainfall during pauses in activity or during dormancy.{{cite journal |last1=Pierson |first1=Thomas C |last2=Wood |first2=Nathan J |last3=Driedger |first3=Carolyn L |title=Reducing risk from lahar hazards: concepts, case studies, and roles for scientists |journal=Journal of Applied Volcanology |date=December 2014 |volume=3 |issue=1 |pages=16 |doi=10.1186/s13617-014-0016-4|bibcode=2014JApV....3...16P |doi-access=free }}{{cite journal |last1=Kataoka |first1=Kyoko S. |last2=Matsumoto |first2=Takane |last3=Saito |first3=Takeshi |last4=Kawashima |first4=Katsuhisa |last5=Nagahashi |first5=Yoshitaka |last6=Iyobe |first6=Tsutomu |last7=Sasaki |first7=Akihiko |last8=Suzuki |first8=Keisuke |title=Lahar characteristics as a function of triggering mechanism at a seasonally snow-clad volcano: contrasting lahars following the 2014 phreatic eruption of Ontake Volcano, Japan |journal=Earth, Planets and Space |date=December 2018 |volume=70 |issue=1 |pages=113 |doi=10.1186/s40623-018-0873-x|bibcode=2018EP&S...70..113K |hdl=2433/234673 |s2cid=135044756 |hdl-access=free |doi-access=free }}

In addition to their variable rheology, lahars vary considerably in magnitude. The Osceola Lahar produced by Mount Rainier in modern-day Washington some 5600 years ago resulted in a wall of mud {{convert|140|m|ft|-1}} deep in the White River canyon and covered an area of over {{convert|330|km2|sqmi|-1}}, for a total volume of {{convert|2.3|km3|mi3|frac=8}}.{{cite journal|last=Crandell|first=D.R.|author-link=Dwight Crandell|year=1971|title=Post glacial lahars From Mount Rainier Volcano, Washington |journal=U.S. Geological Survey Professional Paper|volume=677|url=https://pubs.er.usgs.gov/publication/pp677|doi=10.3133/pp677|series=Professional Paper|doi-access=free}} A debris-flow lahar can erase virtually any structure in its path, while a hyperconcentrated-flow lahar is capable of carving its own pathway, destroying buildings by undermining their foundations. A hyperconcentrated-flow lahar can leave even frail huts standing, while at the same time burying them in mud,{{cite web |last1=Janda |first1=Richard J. |last2=Daag |first2=Arturo S. |last3=Delos Reyes |first3=Perla J. |last4=Newhall |first4=Christopher G. |last5=Pierson |first5=Thomas C. |last6=Punongbayan |first6=Raymundo S. |last7=Rodolfo |first7=Kelvin S. |last8=Solidum |first8=Renato U. |last9=Umbal |first9=Jesse V. |title=Assessment and Response to Lahar Hazard around Mount Pinatubo, 1991 to 1993 |url=https://pubs.usgs.gov/pinatubo/janda/ |website=FIRE and MUD |publisher=United States Geological Survey |access-date=2 July 2021}} which can harden to near-concrete hardness. A lahar's viscosity decreases the longer it flows and can be further thinned by rain, producing a quicksand-like mixture that can remain fluidized for weeks and complicate search and rescue.

Lahars vary in speed. Small lahars less than a few metres wide and several centimetres deep may flow a few metres per second. Large lahars hundreds of metres wide and tens of metres deep can flow several tens of metres per second (22 mph or more), much too fast for people to outrun.{{USGS|title=Lahars and Their Effects|url=http://volcanoes.usgs.gov/hazards/lahar/index.php|access-date=2012-08-23}} On steep slopes, lahar speeds can exceed {{convert|200|km/h|mph|-1}}. A lahar can cause catastrophic destruction along a potential path of more than {{convert|300|km|mi|-1}}.{{cite journal|title=Volcanic hazards with regard to siting nuclear-power plants in the Pacific northwest|last=Hoblitt|first=R.P.|author2=Miller, C.D. |author3=Scott, W.E. |journal=U.S. Geological Survey Open-File Report|volume=87–297|year=1987|doi=10.3133/ofr87297|series=Open-File Report|doi-access=free}}

Lahars from the 1985 Nevado del Ruiz eruption in Colombia caused the Armero tragedy, burying the city of Armero under {{convert|5|m|ft|0}} of mud and debris and killing an estimated 23,000 people.{{cite web|url=http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.html |title=Deadly Lahars from Nevado del Ruiz, Colombia |work=USGS Volcano Hazards Program |access-date=2007-09-02 |archive-url=https://web.archive.org/web/20070824150301/http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.html |archive-date=2007-08-24 |url-status=dead}} A lahar caused New Zealand's Tangiwai disaster,{{cite web | url=http://www.doc.govt.nz/documents/about-doc/concessions-and-permits/conservation-revealed/lahars-from-mt-ruapehu-lowres.pdf | title=Lahars from Mt Ruapehu | publisher=Department of Conservation (New Zealand) | date=2006 | access-date=5 November 2016 | archive-date=26 June 2016 | archive-url=https://web.archive.org/web/20160626215628/http://www.doc.govt.nz/documents/about-doc/concessions-and-permits/conservation-revealed/lahars-from-mt-ruapehu-lowres.pdf | url-status=dead }} where 151 people died after a Christmas Eve express train fell into the Whangaehu River in 1953. Lahars have caused 17% of volcano-related deaths between 1783 and 1997.{{cite journal|last=Tanguy|first=J.|year=1998|title=Victims from volcanic eruptions: a revised database|journal=Bulletin of Volcanology|volume=60|issue=2|page=140|doi=10.1007/s004450050222|bibcode=1998BVol...60..137T|s2cid=129683922|display-authors=etal}}

File:MSH80 mudline muddy river with USGS scientist 10-23-80.jpg left behind on trees on the banks of the Muddy River after the 1980 eruption of Mount St. Helens showing the height of the lahar]]

Lahars have several possible causes:

• Snow and glaciers can be melted by lava or pyroclastic surges during an eruption.
• Lava can erupt from open vents and mix with wet soil, mud or snow on the slope of the volcano making a very viscous, high energy lahar. The higher up the slope of the volcano, the more gravitational potential energy the flows will have.
• A flood caused by a glacier, lake breakout, or heavy rainfalls can generate lahars, also called glacier run or jökulhlaup.
• Water from a crater lake can combine with volcanic material in an eruption.
• Heavy rainfall can mobilize unconsolidated pyroclastic deposits.

In particular, although lahars are typically associated with the effects of volcanic activity, lahars can occur even without any current volcanic activity, as long as the conditions are right to cause the collapse and movement of mud originating from existing volcanic ash deposits.

• Snow and glaciers can melt during periods of mild to hot weather.
• Earthquakes underneath or close to the volcano can shake material loose and cause it to collapse, triggering a lahar avalanche.
• Rainfall can cause the still-hanging slabs of solidified mud to come rushing down the slopes at a speed of more than {{convert|18.64|mph|km/h|1|abbr=on}}, causing devastating results.

File:Galunggung lahar.jpg, Indonesia]]

Several mountains in the world – including Mount Rainier{{Cite web |title=Volcanic Hazards at Mount Rainier {{!}} U.S. Geological Survey |url=https://www.usgs.gov/volcanoes/mount-rainier/volcanic-hazards-mount-rainier |access-date=2022-07-25 |website=www.usgs.gov}} in the United States, Mount Ruapehu in New Zealand, and Merapi{{Cite news|url=http://www.thejakartapost.com/news/2011/01/05/lahar-destroys-farmlands.html|title=Lahar destroys farmlands|work=The Jakarta Post|access-date=2018-06-06|language=en}}{{Cite news|url=https://nasional.kompas.com/read/2011/02/24/2040513/material.lahar.dingin.masih.berbahaya|title=Material Lahar Dingin Masih Berbahaya - Kompas.com|last=Media|first=Kompas Cyber|date=2011-02-24|work=KOMPAS.com|access-date=2018-06-06|language=id}} and Galunggung in Indonesia{{cite journal |last1=Suryo |first1=I. |last2=Clarke |first2=M. C. G. |title=The occurrence and mitigation of volcanic hazards in Indonesia as exemplified at the Mount Merapi, Mount Kelut and Mount Galunggung volcanoes |journal=Quarterly Journal of Engineering Geology and Hydrogeology |date=February 1985 |volume=18 |issue=1 |pages=79–98 |doi=10.1144/GSL.QJEG.1985.018.01.09|s2cid=129879951 }} – are considered particularly dangerous due to the risk of lahars. Several towns in the Puyallup River valley in Washington state, including Orting, are built on top of lahar deposits that are only about 500 years old. Lahars are predicted to flow through the valley every 500 to 1,000 years, so Orting, Sumner, Puyallup, Fife, and the Port of Tacoma face considerable risk.{{cite journal |last1=Wood |first1=Nathan J. |last2=Soulard |first2=Christopher E. |title=Community exposure to lahar hazards from Mount Rainier, Washington |journal=U.S. Geological Survey Scientific Investigations Report |series=Scientific Investigations Report |date=2009 |volume=2009-5211 |pages=34 |doi=10.3133/sir20095211|doi-access=free }} The USGS has set up lahar warning sirens in Pierce County, Washington, so that people can flee an approaching debris flow in the event of a Mount Rainier eruption.{{Cite web|url=https://volcanoes.usgs.gov/volcanoes/mount_rainier/mount_rainier_monitoring_99.html|title=USGS: Volcano Hazards Program CVO Mount Rainier|last=Program|first=Volcano Hazards|website=volcanoes.usgs.gov|access-date=2018-05-24}}

A lahar warning system has been set up at Mount Ruapehu by the New Zealand Department of Conservation and hailed as a success after it successfully alerted officials to an impending lahar on 18 March 2007.{{cite journal |last1=Massey |first1=Christopher I. |last2=Manville |first2=Vernon |last3=Hancox |first3=Graham H. |last4=Keys |first4=Harry J. |last5=Lawrence |first5=Colin |last6=McSaveney |first6=Mauri |title=Out-burst flood (lahar) triggered by retrogressive landsliding, 18 March 2007 at Mt Ruapehu, New Zealand—a successful early warning |journal=Landslides |date=September 2010 |volume=7 |issue=3 |pages=303–315 |doi=10.1007/s10346-009-0180-5|bibcode=2010Lands...7..303M |s2cid=140555437 }}

Since mid-June 1991, when violent eruptions triggered Mount Pinatubo's first lahars in 500 years, a system to monitor and warn of lahars has been in operation. Radio-telemetered rain gauges provide data on rainfall in lahar source regions, acoustic flow monitors on stream banks detect ground vibration as lahars pass, and staffed watchpoints further confirm that lahars are rushing down Pinatubo's slopes. This system has enabled warnings to be sounded for most but not all major lahars at Pinatubo, saving hundreds of lives.{{USGS|url=http://pubs.usgs.gov/fs/1997/fs114-97/|first1=Chris|last1=Newhall|first2=Peter H.|last2=Stauffer|first3=James W, II|last3=Hendley|title=Lahars of Mount Pinatubo, Philippines}} Physical preventative measures by the Philippine government were not adequate to stop over {{convert|20|ft|m|0|order=flip|abbr=on}} of mud from flooding many villages around Mount Pinatubo from 1992 through 1998.{{cite journal |last1=Leone |first1=Frédéric |last2=Gaillard |first2=Jean-Christophe |title=Analysis of the institutional and social responses to the eruption and the lahars of Mount Pinatubo volcano from 1991 to 1998 (Central Luzon, Philippines) |journal=GeoJournal |date=1999 |volume=49 |issue=2 |pages=223–238 |doi=10.1023/A:1007076704752|s2cid=152999296 }}

Scientists and governments try to identify areas with a high risk of lahars based on historical events and computer models. Volcano scientists play a critical role in effective hazard education by informing officials and the public about realistic hazard probabilities and scenarios (including potential magnitude, timing, and impacts); by helping evaluate the effectiveness of proposed risk-reduction strategies; by helping promote acceptance of (and confidence in) hazards information through participatory engagement with officials and vulnerable communities as partners in risk reduction efforts; and by communicating with emergency managers during extreme events.{{sfn|Pierson|Wood |Driedger|2014}} An example of such a model is TITAN2D.{{cite journal |last1=Pitman |first1=E. Bruce |last2=Nichita |first2=C. Camil |last3=Patra |first3=Abani |last4=Bauer |first4=Andy |last5=Sheridan |first5=Michael |last6=Bursik |first6=Marcus |title=Computing granular avalanches and landslides |journal=Physics of Fluids |date=December 2003 |volume=15 |issue=12 |pages=3638–3646 |doi=10.1063/1.1614253|bibcode=2003PhFl...15.3638P }} These models are directed towards future planning: identifying low-risk regions to place community buildings, discovering how to mitigate lahars with dams, and constructing evacuation plans.{{cite journal |last1=Huggel |first1=C. |last2=Schneider |first2=D. |last3=Miranda |first3=P. Julio |last4=Delgado Granados |first4=H. |last5=Kääb |first5=A. |title=Evaluation of ASTER and SRTM DEM data for lahar modeling: A case study on lahars from Popocatépetl Volcano, Mexico |journal=Journal of Volcanology and Geothermal Research |date=February 2008 |volume=170 |issue=1–2 |pages=99–110 |doi=10.1016/j.jvolgeores.2007.09.005 |bibcode=2008JVGR..170...99H |s2cid=51845260 |url=https://www.zora.uzh.ch/id/eprint/5453/2/Huggel_Schneider_Evaluation_ASTER_2008V.pdf |access-date=2021-07-06 |archive-date=2022-05-03 |archive-url=https://web.archive.org/web/20220503140540/https://www.zora.uzh.ch/id/eprint/5453/2/Huggel_Schneider_Evaluation_ASTER_2008V.pdf |url-status=dead }}

{{main|Armero tragedy}}

Image:Armero aftermath Marso.jpg that wiped out the town of Armero in Colombia]]

In 1985, the volcano Nevado del Ruiz erupted in central Colombia. As pyroclastic flows erupted from the volcano's crater, they melted the mountain's glaciers, sending four enormous lahars down its slopes at {{convert|60|km/h|mph||sp=us|abbr=off}}. The lahars picked up speed in gullies and coursed into the six major rivers at the base of the volcano; they engulfed the town of Armero, killing more than 20,000 of its almost 29,000 inhabitants.{{USGS|last1=Schuster|first1=Robert L.|last2=Highland|first2=Lynn M.|year=2001|url=http://pubs.usgs.gov/of/2001/ofr-01-0276/|title=Socioeconomic and Environmental Impacts of Landslides in the Western Hemisphere|id=Open-File Report 01-0276|access-date=June 11, 2010}}

Casualties in other towns, particularly Chinchiná, brought the overall death toll to over 25,000.{{cite journal|bibcode= 2015AGUFM.G41A1017R|title= Terrestrial Radar Interferometry and Structure-from-Motion Data from Nevado del Ruiz, Colombia for Improved Hazard Assessment and Volcano Monitoring|last1= Rodgers|first1= M.|last2= Dixon|first2= T. H.|last3= Gallant|first3= E.|last4= López|first4= C. M.|last5= Malservisi|first5= R.|last6= Ordoñez|first6= M.|last7= Richardson|first7= J. A.|last8= Voss|first8= N. K.|last9= Xie|first9= S.|journal= AGU Fall Meeting Abstracts|year= 2015|volume= 2015}} Footage and photographs of Omayra Sánchez, a young victim of the tragedy, were published around the world.{{cite news |url=https://www.worldpressphoto.org/collection/photocontest/winners/1986 |title=World Photo Award |date=February 7, 1986 |access-date=April 19, 2011 |work=Spartanburg Herald-Journal }} Other photographs of the lahars and the impact of the disaster captured attention worldwide and led to controversy over the degree to which the Colombian government was responsible for the disaster.{{cite web |url=http://lasa.international.pitt.edu/members/congress-papers/lasa2009/files/ZeidermanAustin.pdf |title=Life at Risk: Biopolitics, Citizenship, and Security in Colombia |last=Zeiderman |first=Austin |work=2009 Congress of the Latin American Studies Association |date=June 11, 2009 |access-date=July 22, 2010}}

{{main|1991 eruption of Mount Pinatubo}}

File:River valley filled in by pyroclastic flows, Mt. Pinatubo.jpg

Lahars caused most of the deaths of the 1991 eruption of Mount Pinatubo. The initial eruption killed six people, but the lahars killed more than 1500. The eye of Typhoon Yunya passed over the volcano during its eruption on 15 June 1991, and the resulting rain triggered the flow of volcanic ash, boulders, and water down rivers surrounding the volcano. Angeles City in Pampanga and neighbouring cities and towns were damaged by lahars when Sapang Balen Creek and the Abacan River became channels for mudflows and carried them to the heart of the city and surrounding areas.{{cite web |last1=Major |first1=Jon J. |last2=Janda |first2=Richard J. |last3=Daag |first3=Arturo S. |title=Watershed Disturbance and Lahars on the East Side of Mount Pinatubo During the mid-June 1991 Eruptions |url=https://pubs.usgs.gov/pinatubo/major/ |website=FIRE and MUD |publisher=United States Geological Survey |access-date=2 July 2021 |date=1996}}

Over {{convert|20|ft|m|0|order=flip}} of mud inundated and damaged the towns of Castillejos, San Marcelino and Botolan in Zambales, Porac and Mabalacat in Pampanga, Tarlac City, Capas, Concepcion and Bamban in Tarlac. The Bamban Bridge on the MacArthur Highway, a major north–south transportation route, was destroyed, and temporary bridges erected in its place were inundated by subsequent lahars.{{cite web |last1=Martinez |first1=Ma. Mylene L. |last2=Arboleda |first2=Ronaldo A. |last3=Delos Reyes |first3=Perla J. |last4=Gabinete |first4=Elmer |last5=Dolan |first5=Michael T. |title=Observations of 1992 Lahars along the Sacobia-Bamban River System |url=https://pubs.usgs.gov/pinatubo/martinez/ |website=FIRE and MUD |publisher=United States Geological Survey |access-date=2 July 2021}}

On the morning of 1 October 1995, pyroclastic material which clung to the slopes of Pinatubo and surrounding mountains rushed down because of heavy rain, and turned into an {{convert|25|ft|m|0|adj=on|order=flip}} lahar. This mudflow killed at least 100 people in Barangay Cabalantian in Bacolor.{{cite journal |last1=Gudmundsson |first1=Magnús T. |title=Hazards from Lahars and Jökulhlaups |journal=The Encyclopedia of Volcanoes |date=2015 |pages=971–984 |doi=10.1016/B978-0-12-385938-9.00056-0|isbn=9780123859389 }} The Philippine government under President Fidel V. Ramos ordered the construction of the FVR Mega Dike in an attempt to protect people from further mudflows.{{cite web |last1=Isip |first1=Rendy |title=FVR mega dike still under threat of lahar |url=https://iorbitnews.com/fvr-mega-dike-still-threat-lahar/ |website=iOrbit News Online |access-date=2 July 2021 |date=24 June 2016}}

Typhoon Reming triggered additional lahars in the Philippines in 2006.{{cite web|author=Steve Lang|year=2006|title=Typhoon Durian Triggers Massive Mudslides in the Philippines|publisher=NASA|access-date=February 20, 2007|url=http://www.nasa.gov/mission_pages/hurricanes/archives/2006/h2006_durian.html |quote=known as "Reming" in the Philippines}}

• Volcanic hazard
• Mass wasting
• Polder
• Land reclamation

{{reflist|30em}}

{{Wiktionary|lahar}}

{{Commonscat|Lahars}}

• [http://www.geography-site.co.uk/pages/physical/earth/volcanoes/pyroclastic%20flows.html Schools page about lahars and pyroclastic flows]
• [http://volcanoes.usgs.gov/images/pglossary/lahar.php USGS web page about lahars]
• [http://volcanoes.usgs.gov/volcanoes/mount_rainier/ Mount Rainier, Washington]
• [http://pubs.usgs.gov/fs/2008/3062/ USGS fact sheet – "Mount Rainier – Living Safely With a Volcano in Your Back Yard"]

{{Natural disasters}}

Category:Volcanism