Everything about Lahar totally explained
A
lahar is a type of
mudflow composed of
pyroclastic material and
water that flows down from a
volcano, typically along a
river valley. The term 'lahar' originated in the
Javanese language of
Indonesia.
Lahars have the consistency of
concrete: fluid when moving, then solid when stopped. Lahars can be huge: the Osceola lahar produced 5,600 years ago by
Mount Rainier in
Washington produced a wall of mud deep in the
White River canyon and extends over an area of over for a total volume of 2.3 cubic kilometers (0.55 cubic miles).
Lahars can be extremely dangerous, because of their energy and speed. Large lahars can flow several dozen meters per second and can flow for many kilometres, causing catastrophic destruction in their path. The lahars from the
Nevado del Ruiz eruption in
Colombia in
1985 caused the
Armero tragedy, which killed an estimated 23,000 when the city of
Armero was buried under of mud and debris. The
1953 Tangiwai disaster in
New Zealand was caused by a lahar.
Lahars have several possible causes:
- Snow and glaciers can be melted by a pyroclastic flow during an eruption
- A flood caused by a glacier, lake breakout, or heavy rainfall can release a lahar, also called glacier run or jökulhlaup.
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.
Several mountains in the world, including
Mount Rainier in the
USA,
Mount Ruapehu in
New Zealand, and
Galunggung in
Indonesia, are considered particularly dangerous due to the risk of lahars. Several towns in the
Puyallup River valley in Washington state, including
Orting, the closest to Mount Rainier, are built on top of lahar deposits that are only about 500 years old. Lahars are predicted to flow through the valley every 500-1,000 years, so Orting,
Sumner,
Puyallup,
Fife, and the Port of
Tacoma face considerable risk.
The
USGS has set up lahar warning sirens in
Pierce County, so that people can flee an approaching debris flow.
A lahar warning system has been set up at Mount Ruapehu by the
New Zealand Department of Conservation and hailed a success after it successfully alerted officials to an impending lahar on 18 March 2007.
The
1991 Mount Pinatubo eruption caused lahar as well, but it was due to the passing of a major
typhoon over the
Philippines which resulted in a torrent of
volcanic ash and
water down to the
rivers surrounding the
volcano. The lahar was caused by the mixing of settled ash and water from the monsoon which occurred the day after the volcano finished erupting. Although the eruption only killed 6 people, 1500 were killed in the resulting lahar, showing the destructive nature of lahars.
Further Information
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