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Earthquake on June 6, 1994,
Triggers Landslides and Catastrophic Lahar
Near Nevado del Huila Volcano, Colombia

Landslide scars on hillslopes above R?o Paez, near Huila Volcano, Colombia
Photograph by R.L. Schuster on July 3, 1994

Brown-colored scars on steep hillsides sweep into the R?o Paez at the base of Nevado del Huila (elevation 5,262 m), a large volcanic complex in Colombia. The scars are pathways of dozens of landslides that removed wet soil, volcanic ash, and vegetation from the hillsides and produced a destructive lahar in the R?o Paez valley (flowing toward bottom of photograph). The southwest flank of the volcano is visible in upper left.

Within minutes of a magnitude 6.4 earthquake beneath the SSW flank of Nevado del Huila volcano, dozens of landslides swept from the steep valleys above R?o Paez into the river. The landslides quickly turned into debris flows, which joined to produce a single enormous flow of water, rocks, soil, and trees in R?o Paez. The lahar destroyed most or parts of several towns along the river, including Dublin, Irlanda, Toez, and Belalcazar, killed several hundred people, and displaced about 20,000 people from their homes. Six bridges and >100 km of roads were destroyed.

The huge flow wave originated from both hydrothermally altered rocks of Huila Volcano and the ash-mantled terrain surrounding the volcano. Whether triggered by a large earthquake, intense rainfall (for example, see Casita Volcano), or both, this tragic event illustrates that both volcanic cones and steep hillslopes around them can collapse to form landslides and debris flows.

People from around the world have repeatedly sensed an approaching lahar as a rumbling noise or ground vibration. In some cases, had they known the cause of the noise and tremor, people killed by lahars may have had time to get to high ground before it reached them. In the case of lahars triggered by a large earthquake, people often mistake the shaking of the ground from an approaching lahar as a second earthquake, and so they stayed where they were. People living in valleys downstream from mountainous volcanic terrains can reduce their risk by moving immmediately to high ground for a few hours after a strong earthquake--just in case a destructive flow is headed their way. This strategy is very important for communities located at the mouth of a tributary canyon, an area that can be swept by lahars from both the canyon and the main river valley.

Map of Nevado del Huila volcano and path of 1994 lahar in R?o Paez

Scars of landslides that merged together to form lahar on June 6, 1994 Brown scars mark landslide pathways on steep slopes above R?o Paez.

Close view of landslides that did not reach R?o Paez Some landslides did not contribute to the main lahar in R?o Paez.

R?o Paez and town of Islanda swept by lahar on June 6, 1994 Lahar traveled down R?o Paez and destroyed town of Irlanda.

Town of Irlanda, Colombia, swept by lahar on June 6, 1994 Closer view of main lahar at Irlanda.

Town of Toez hit by lahar, R?o Paez, Colombia Lahar overruns town of Toez within 10 minutes of the earthquake.

Town of Toez, Colombia, struck by earthquake and swept by lahar on June 6, 1994 Earthquake damages structures before lahar arrives.

Building hit by lahar on June 6, 1994, along R?o Paez, Colombia Tremendous impact force of the lahar hits barn and other structures.

Town of Belalcazar, largest community hit by lahar in R?o Paez, Colombia Town of Belalcazar, largest community hit by lahar in R?o Paez, Colombia.


Other landslides and lahars


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U.S. Department of the Interior, U.S. Geological Survey, Menlo Park, California, USA
URL http://volcanoes.usgs.gov/Hazards/What/Lahars/HuilaLahar.html
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Last modification: 20 June 2002 (SRB)