Lahar
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 and Nevado del Ruiz, the latter of which killed thousands of people in the town of Armero.
Etymology
The word lahar is of Javanese origin.[2] Berend George Escher introduced it as a geological term in 1922.[3]
Description
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
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
Lahars have several possible causes:[9]
- 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 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.
- Earthquakesunderneath or close to the volcano can shake material loose and cause it to collapse, triggering a lahar avalanche.
- Rainfallcan cause the still-hanging slabs of solidified mud to come rushing down the slopes at a speed of more than 18.64 mph (30.0 km/h), causing devastating results.
Places at risk
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
Since mid-June 1991, when violent eruptions triggered
Scientists and governments try to identify areas with a high risk of lahars based on historical events and
Examples
Nevado del Ruiz
In 1985, the volcano
Casualties in other towns, particularly
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
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
See also
References
- ^ "Lahar". USGS Photo Glossary. Retrieved 2009-04-19.
- ISBN 978-0-12-385938-9.
- ISBN 9780415327381.
- ^ ISBN 978-0-12-385938-9, retrieved 2021-03-26
- ^ .
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- ^ 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.
- ^ a b c This article incorporates public domain material from Lahars and Their Effects. United States Geological Survey. Retrieved 2012-08-23.
- doi:10.3133/ofr87297.
- ^ "Deadly Lahars from Nevado del Ruiz, Colombia". USGS Volcano Hazards Program. Archived from the original on 2007-08-24. Retrieved 2007-09-02.
- ^ "Lahars from Mt Ruapehu" (PDF). Department of Conservation (New Zealand). 2006. Archived from the original (PDF) on 26 June 2016. Retrieved 5 November 2016.
- S2CID 129683922.
- ^ "Volcanic Hazards at Mount Rainier | U.S. Geological Survey". www.usgs.gov. Retrieved 2022-07-25.
- ^ "Lahar destroys farmlands". The Jakarta Post. Retrieved 2018-06-06.
- ^ Media, Kompas Cyber (2011-02-24). "Material Lahar Dingin Masih Berbahaya - Kompas.com". KOMPAS.com (in Indonesian). Retrieved 2018-06-06.
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- ^ Program, Volcano Hazards. "USGS: Volcano Hazards Program CVO Mount Rainier". volcanoes.usgs.gov. Retrieved 2018-05-24.
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- ^ 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}}
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- ^ Pierson, Wood & Driedger 2014.
- .
- S2CID 51845260. Archived from the original(PDF) on 2022-05-03. Retrieved 2021-07-06.
- ^ 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.
- Bibcode:2015AGUFM.G41A1017R.
- ^ "World Photo Award". Spartanburg Herald-Journal. February 7, 1986. Retrieved April 19, 2011.
- ^ 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.
- ^ 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.
- ^ 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.
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- ^ Isip, Rendy (24 June 2016). "FVR mega dike still under threat of lahar". iOrbit News Online. Retrieved 2 July 2021.
- ^ Steve Lang (2006). "Typhoon Durian Triggers Massive Mudslides in the Philippines". NASA. Retrieved February 20, 2007.
known as "Reming" in the Philippines