Lahars

The Challenges of Predicting and Eruption
1. Does the current unrest involve magma movement?
2. If yes, when will the eruption occur (if at all)?
3. What warnings are necessary?
4. When is the eruption really over?
Lahars
http://www.geo.mtu.edu/volcanoes/pinatubo/lahar/scan-008.gif
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/MSHPPF/MSH_past_present_future.html
http://www.geo.mtu.edu/volcanoes/pinatubo/lahar/
A lahar is a volcanic mudflow, usually associated with
stratovolcanoes (because of more snow and ice)
The word lahar comes from Indonesia, referring
to mudflows that are volcanic in origin.
http://www.geo.mtu.edu/volcanoes/pinatubo/lahar/
Mount Rainier
Mount Rainier
Lahars can develop from three processes:
1. Melting snow and ice during volcanic activity (e.g., Mount Rainier)
2. Heavy Rain on ash deposits (e.g., Mount Pinatubo)
3. Volcanic landslides generated by EQs etc. (e.g., Nevado del Huila)
Earthquake on June 6, 1994,
Triggers Landslides and
Catastrophic Lahar Near Nevado
del Huila Volcano, Colombia
http://volcanoes.usgs.gov/hazards/lahar/huila.php
Pasig-Potrero River on the east side of Pinatubo volcano in
the Philippines on October 13, 1991.
http://www.volcano.si.edu/world/tpgallery.cfm?category=Lahars%20(mudflows)&photo=019028
The towns of Barangay Manibaug Pasig, Phillippines in the
foreground and Mancatian in the distance were progressively
buried over a several-year period (Feb 1994).
The towns of Barangay Manibaug Pasig, in the foreground of this February 26, 1994 view, and
Mancatian in the distance were progressively buried over a several-year period.
Floodwaters back up over the villages of Aglao and
Dalanawan on the SW flank of Pinatubo volcano in the
Philippines.
The towns of Barangay Manibaug Pasig, in the foreground of this February 26, 1994 view, and
Mancatian in the distance were progressively buried over a several-year period.
Sediment deposits raise river channels causing floods.
Lahar deposits on Mount
Pinatubo 10 years after the
eruption on June 15, 1991
http://earthobservatory.nasa.gov/IOTD/view.php?id=1512
Lahar deposits on Lahar on
Mount Ruapehu, New
Zealand March 25, 2007
http://earthobservatory.nasa.gov/IOTD/view.php?id=1512
More than 23,000 people were killed in
Armero, Colombia when lahars swept
down from the erupting Nevado del Ruiz
volcano on November 13, 1985.
Lahars are the most probable volcanic hazard
on Mount Rainier
Lahars follow low
topographic regions
like river valleys.
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Mitigation: Hazard Maps
Lahars follow river drainages
Orting, WA Evacuation Plan
Mitigation: Acoustic Flow Monitors (AFMs)
Mount Rainier has 40 or so AFMs
Seismometer senses ground vibrations due to an
on-coming lahar.
Lahars formed during the 1989-90 eruptions of
Redoubt Volcano in Alaska
http://www.volcano.si.edu/world/tpgallery.cfm?category=Lahars%20(mudflows)&photo=052042
The 1990 eruption triggered a lahar at Redoubt Volcano that was
detected by 3 AFMs that had been installed a few months earlier.
Lahars are the greatest hazard at Mount Baker
http://www.pbase.com/nolock/image/94450294
Lahars have occurred on Mount Baker in the past
Carbon dating of logs
yielded an age of the
lahar at about 5800
years before present.
Deposit of the largest lahar from confluence of the Middle and
North Forks of the Nooksack River, about 20 miles from its
source at the Roman Wall. Note the protruding logs and
branches from living trees that were knocked down and carried
by the lahar. Ice axe, 3 ft, shows scale.
Bellingham
Sedro Wooley
Mt. Baker
Lynden
Nooksack River
Skagit River
Baker Lake
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