A lahar travels down a river valley in Guatemala near the Santa Maria volcano, 1989

A lahar ( /ˈlɑːhɑːr/, from Javanese: ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.[1]

Lahars can be extremely destructive: they can flow tens of metres per second, they have been known to be up to 140 metres (460 ft) deep, and large flows tend to destroy any structures in their path. Notable lahars include those at Mount Pinatubo in the Philippines and Nevado del Ruiz in Colombia, the latter of which killed thousands of people in the town of Armero.


The word lahar is of Javanese origin.[2] Berend George Escher introduced it as a geological term in 1922.[3]


Excavated 9th century Sambisari 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.[4] 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.[4] 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.[5][6]

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 140 metres (460 ft) deep in the White River canyon and covered an area of over 330 square kilometres (130 sq mi), for a total volume of 2.3 cubic kilometres (12 cu mi).[7] 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.[5] A hyperconcentrated-flow lahar can leave even frail huts standing, while at the same time burying them in mud,[8] 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.[5]

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.[9] On steep slopes, lahar speeds can exceed 200 kilometres per hour (120 mph).[9] A lahar can cause catastrophic destruction along a potential path of more than 300 kilometres (190 mi).[10]

Lahars from the 1985 Nevado del Ruiz eruption in Colombia caused the Armero tragedy, burying the city of Armero under 5 metres (16 ft) of mud and debris and killing an estimated 23,000 people.[11] A lahar caused New Zealand's Tangiwai disaster,[12] 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.[13]

Trigger mechanisms

Mudline 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:[9]

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.

Places at risk

The aftermath of a lahar from the 1982 eruption of Galunggung, Indonesia

Several mountains in the world – including Mount Rainier[14] in the United States, Mount Ruapehu in New Zealand, and Merapi[15][16] and Galunggung in Indonesia[17] – 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.[18] 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.[19]

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.[20]

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.[21] Physical preventative measures by the Philippine government were not adequate to stop over 6 m (20 ft) of mud from flooding many villages around Mount Pinatubo from 1992 through 1998.[22]

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.[23] An example of such a model is TITAN2D.[24] 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.[25]


Nevado del Ruiz

Main article: Armero tragedy

The lahar from the 1985 eruption of Nevado del Ruiz 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 60 kilometers per hour (37 miles per hour). 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.[26]

Casualties in other towns, particularly Chinchiná, brought the overall death toll to over 25,000.[27] Footage and photographs of Omayra Sánchez, a young victim of the tragedy, were published around the world.[28] 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.[29]

Mount Pinatubo

Main article: 1991 eruption of Mount Pinatubo

A before-and-after photograph of a river valley filled in by lahars from Mount Pinatubo

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.[30]

Over 6 metres (20 ft) 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.[8] 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.[31]

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 8-metre (25 ft) lahar. This mudflow killed at least 100 people in Barangay Cabalantian in Bacolor.[32] 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.[33]

Typhoon Reming triggered additional lahars in the Philippines in 2006.[34]

See also


  1. ^ "Lahar". USGS Photo Glossary. Retrieved 2009-04-19.
  2. ^ Vallance, James W.; Iverson, Richard M. (2015). "Chapter 37 – Lahars and Their Deposits". In Sigurdsson, Haraldur (ed.). Encyclopedia of Volcanoes. Amsterdam: Academic Press. pp. 649–664. doi:10.1016/B978-0-12-385938-9.00037-7. ISBN 978-0-12-385938-9.
  3. ^ Vincent E. Neall (2004). "Lahar". In Andrew S. Goudie (ed.). Encyclopedia of Geomorphology. Vol. 2. Psychology Press. pp. 597–599. ISBN 9780415327381.
  4. ^ a b Vallance, James W.; Iverson, Richard M. (2015-01-01), "Chapter 37 - Lahars and Their Deposits", in Sigurdsson, Haraldur (ed.), The Encyclopedia of Volcanoes (Second Edition), Amsterdam: Academic Press, pp. 649–664, ISBN 978-0-12-385938-9, retrieved 2021-03-26
  5. ^ a b c Pierson, Thomas C; Wood, Nathan J; Driedger, Carolyn L (December 2014). "Reducing risk from lahar hazards: concepts, case studies, and roles for scientists". Journal of Applied Volcanology. 3 (1): 16. Bibcode:2014JApV....3...16P. doi:10.1186/s13617-014-0016-4.
  6. ^ Kataoka, Kyoko S.; Matsumoto, Takane; Saito, Takeshi; Kawashima, Katsuhisa; Nagahashi, Yoshitaka; Iyobe, Tsutomu; Sasaki, Akihiko; Suzuki, Keisuke (December 2018). "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". Earth, Planets and Space. 70 (1): 113. Bibcode:2018EP&S...70..113K. doi:10.1186/s40623-018-0873-x. hdl:2433/234673. S2CID 135044756.
  7. ^ Crandell, D.R. (1971). "Post glacial lahars From Mount Rainier Volcano, Washington". U.S. Geological Survey Professional Paper. Professional Paper. 677. doi:10.3133/pp677.
  8. ^ a b Janda, Richard J.; Daag, Arturo S.; Delos Reyes, Perla J.; Newhall, Christopher G.; Pierson, Thomas C.; Punongbayan, Raymundo S.; Rodolfo, Kelvin S.; Solidum, Renato U.; Umbal, Jesse V. "Assessment and Response to Lahar Hazard around Mount Pinatubo, 1991 to 1993". FIRE and MUD. United States Geological Survey. Retrieved 2 July 2021.
  9. ^ a b c Public Domain This article incorporates public domain material from Lahars and Their Effects. United States Geological Survey. Retrieved 2012-08-23.
  10. ^ Hoblitt, R.P.; Miller, C.D.; Scott, W.E. (1987). "Volcanic hazards with regard to siting nuclear-power plants in the Pacific northwest". U.S. Geological Survey Open-File Report. Open-File Report. 87–297. doi:10.3133/ofr87297.
  11. ^ "Deadly Lahars from Nevado del Ruiz, Colombia". USGS Volcano Hazards Program. Archived from the original on 2007-08-24. Retrieved 2007-09-02.
  12. ^ "Lahars from Mt Ruapehu" (PDF). Department of Conservation (New Zealand). 2006. Archived from the original (PDF) on 26 June 2016. Retrieved 5 November 2016.
  13. ^ Tanguy, J.; et al. (1998). "Victims from volcanic eruptions: a revised database". Bulletin of Volcanology. 60 (2): 140. Bibcode:1998BVol...60..137T. doi:10.1007/s004450050222. S2CID 129683922.
  14. ^ "Volcanic Hazards at Mount Rainier | U.S. Geological Survey". www.usgs.gov. Retrieved 2022-07-25.
  15. ^ "Lahar destroys farmlands". The Jakarta Post. Retrieved 2018-06-06.
  16. ^ Media, Kompas Cyber (2011-02-24). "Material Lahar Dingin Masih Berbahaya - Kompas.com". KOMPAS.com (in Indonesian). Retrieved 2018-06-06.
  17. ^ Suryo, I.; Clarke, M. C. G. (February 1985). "The occurrence and mitigation of volcanic hazards in Indonesia as exemplified at the Mount Merapi, Mount Kelut and Mount Galunggung volcanoes". Quarterly Journal of Engineering Geology and Hydrogeology. 18 (1): 79–98. doi:10.1144/GSL.QJEG.1985.018.01.09. S2CID 129879951.
  18. ^ Wood, Nathan J.; Soulard, Christopher E. (2009). "Community exposure to lahar hazards from Mount Rainier, Washington". U.S. Geological Survey Scientific Investigations Report. Scientific Investigations Report. 2009–5211: 34. doi:10.3133/sir20095211.
  19. ^ Program, Volcano Hazards. "USGS: Volcano Hazards Program CVO Mount Rainier". volcanoes.usgs.gov. Retrieved 2018-05-24.
  20. ^ Massey, Christopher I.; Manville, Vernon; Hancox, Graham H.; Keys, Harry J.; Lawrence, Colin; McSaveney, Mauri (September 2010). "Out-burst flood (lahar) triggered by retrogressive landsliding, 18 March 2007 at Mt Ruapehu, New Zealand—a successful early warning". Landslides. 7 (3): 303–315. Bibcode:2010Lands...7..303M. doi:10.1007/s10346-009-0180-5. S2CID 140555437.
  21. ^ Public Domain This article incorporates public domain material from Newhall, Chris; Stauffer, Peter H.; Hendley, James W, II. Lahars of Mount Pinatubo, Philippines. United States Geological Survey.((citation)): CS1 maint: multiple names: authors list (link)
  22. ^ Leone, Frédéric; Gaillard, Jean-Christophe (1999). "Analysis of the institutional and social responses to the eruption and the lahars of Mount Pinatubo volcano from 1991 to 1998 (Central Luzon, Philippines)". GeoJournal. 49 (2): 223–238. doi:10.1023/A:1007076704752. S2CID 152999296.
  23. ^ Pierson, Wood & Driedger 2014.
  24. ^ Pitman, E. Bruce; Nichita, C. Camil; Patra, Abani; Bauer, Andy; Sheridan, Michael; Bursik, Marcus (December 2003). "Computing granular avalanches and landslides". Physics of Fluids. 15 (12): 3638–3646. Bibcode:2003PhFl...15.3638P. doi:10.1063/1.1614253.
  25. ^ Huggel, C.; Schneider, D.; Miranda, P. Julio; Delgado Granados, H.; Kääb, A. (February 2008). "Evaluation of ASTER and SRTM DEM data for lahar modeling: A case study on lahars from Popocatépetl Volcano, Mexico" (PDF). Journal of Volcanology and Geothermal Research. 170 (1–2): 99–110. Bibcode:2008JVGR..170...99H. doi:10.1016/j.jvolgeores.2007.09.005. S2CID 51845260. Archived from the original (PDF) on 2022-05-03. Retrieved 2021-07-06.
  26. ^ Public Domain This article incorporates public domain material from Schuster, Robert L.; Highland, Lynn M. (2001). Socioeconomic and Environmental Impacts of Landslides in the Western Hemisphere. United States Geological Survey. Open-File Report 01-0276. Retrieved June 11, 2010.
  27. ^ Rodgers, M.; Dixon, T. H.; Gallant, E.; López, C. M.; Malservisi, R.; Ordoñez, M.; Richardson, J. A.; Voss, N. K.; Xie, S. (2015). "Terrestrial Radar Interferometry and Structure-from-Motion Data from Nevado del Ruiz, Colombia for Improved Hazard Assessment and Volcano Monitoring". AGU Fall Meeting Abstracts. 2015. Bibcode:2015AGUFM.G41A1017R.
  28. ^ "World Photo Award". Spartanburg Herald-Journal. February 7, 1986. Retrieved April 19, 2011.
  29. ^ Zeiderman, Austin (June 11, 2009). "Life at Risk: Biopolitics, Citizenship, and Security in Colombia" (PDF). 2009 Congress of the Latin American Studies Association. Retrieved July 22, 2010.
  30. ^ Major, Jon J.; Janda, Richard J.; Daag, Arturo S. (1996). "Watershed Disturbance and Lahars on the East Side of Mount Pinatubo During the mid-June 1991 Eruptions". FIRE and MUD. United States Geological Survey. Retrieved 2 July 2021.
  31. ^ Martinez, Ma. Mylene L.; Arboleda, Ronaldo A.; Delos Reyes, Perla J.; Gabinete, Elmer; Dolan, Michael T. "Observations of 1992 Lahars along the Sacobia-Bamban River System". FIRE and MUD. United States Geological Survey. Retrieved 2 July 2021.
  32. ^ Gudmundsson, Magnús T. (2015). "Hazards from Lahars and Jökulhlaups". The Encyclopedia of Volcanoes: 971–984. doi:10.1016/B978-0-12-385938-9.00056-0. ISBN 9780123859389.
  33. ^ Isip, Rendy (24 June 2016). "FVR mega dike still under threat of lahar". iOrbit News Online. Retrieved 2 July 2021.
  34. ^ Steve Lang (2006). "Typhoon Durian Triggers Massive Mudslides in the Philippines". NASA. Retrieved February 20, 2007. known as "Reming" in the Philippines