11:32 am - Monday May 28, 2012

Lahar

A lahar is a 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.

“Lahar” is an Indonesian word that describes volcanic mudflows or debris flows. Lahars have the consistency, viscosity and approximately the same density of concrete: fluid when moving, then solid when stopped.[3] Lahars can be huge: the Osceola lahar produced 5,600 years ago by Mount Rainier in Washington produced 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 (0.55 cu mi), and can bulldoze through virtually any structure in its path. A lahar is capable of carving its own pathway, making the prediction of its course difficult. A Lahar quickly loses force when it leaves the channel of its flow: even frail huts may remain standing while being buried up to the roof with mud. The viscosity of a lahar decreases with time and amount of rain, although the mud solidifies quickly when it stops moving.

Lahar flows can be deadly because of their energy and speed. They can flow up to approximately 100 kilometres per hour (60 mph), can flow for more than 300 kilometres (190 mi), and can cause 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 5 metres (16 ft) of mud and debris. New Zealand’s Tangiwai disaster in 1953, where 151 people died after a Christmas Eve express train fell into the Whangaehu River, was caused by a lahar. Lahars have been responsible for 17% of volcano-related deaths between 1783 and 1997. Lahars can cause fatalities years after an actual eruption: for example, the Cabalantian tragedy four years after the 1991 eruption of Mount Pinatubo.

Causes of Lahar

Lahars have several possible causes:
1. Snow and glaciers can be melted by lava or pyroclastic flows during an eruption
2. A flood caused by a glacier, lake breakout, or heavy rainfall can release a lahar, also called glacier run or jökulhlaup
3. Water from a crater lake, combined with volcanic material in an eruption

Effects of Lahar

Lahars racing down river valleys and spreading across flood plains tens of kilometers downstream from a volcano often cause serious economic and environmental damage. The direct impact of a lahar’s turbulent flow front or from the boulders and logs carried by the lahar can easily crush, abrade, or shear off at ground level just about anything in the path of a lahar. Even if not crushed or carried away by the force of a lahar, buildings and valuable land may become partially or completely buried by one or more cement-like layers of rock debris. By destroying bridges and key roads, lahars can also trap people in areas vulnerable to other hazardous volcanic activity, especially if the lahars leave deposits that are too deep, too soft, or too hot to cross.

Lahar Videos & Images

Here you can find latest video & images of famous Lahar.

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