Geology And Geophysics

Lahars



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The Earth rumbles, grumbles, snorts, and regurgitates- it spews hot liquids and poisonous gases. It throws rocks. It tears at land by winds. It rains flood in some places while denying any moisture in others. It is as if the earth is at war with itself. Trapped within this war are the creatures that inhabit the planet. Thinking man can do little about most of these natural events except to observe and marvel. Weather, volcano eruption, and earthquakes happen. These natural phenomenon cannot be controlled or predicted. As human knowledge grows, man devises means to deal with natural events. The mystery of natural events leave room for speculation. When the ground moves underfoot, a natural disaster is possible.

Landslides can be attributed to a variety of natural phenomenon. Too much rain or not enough rain can create a condition that causes the topsoil to slide downhill. Technically not land but snow builds up and an avalanche can occur. Earthquakes can course shifts in the earth resulting in landslides. Lahar is an Indonesian word that describes a particular type of earth flow. Lahars are a mixture of water, soil and rock. Lahars are associated with volcanic activity. These Lahars are natural events that have the potential to be a natural disaster.

Lahars are associated with volcanoes. Lahars can be divided into groups based on volcanic activity. Lahars may form before an eruption due avalanches of melted snow or heavy rain that pick up loose volcanic debris and slides down the slope of the volcano. During an eruption the water and debris that is released congeals into a concrete-like flow that slides down the mountainside. After an eruption, the heat and rumbling associated with a volcano can cause melted snow, ash and rock to flow down the mountainside.

Depending on the mixture, Lahars can move as little as one mile an hour to better than 60 miles an hour. The lahar can race along a valley swallowing houses and villages. As the energy is depleted and the temperature cools, the lahar mixture solidifies into a solid concrete mass. Lahars can be massive and devastating. The 1985 Colombian lahar buried the city of Amero under 16 feet of mud and debris. 23,000 lives were lost. Evidence indicates that even larger lahars occurred in the past. The Osceola lahar near Mount Rainier, Washington produced a 460 foot deep mass covering an area of 138 square miles. Excavations continue in Pompey that reveals a village entirely covered in the muddy sludge lahar of Mt Vesuvius.

Technology has helped improve the early detection of lahars. Visual sightings have been replaced with sensors that detect the early movement of lahars. The systems have been installed in countries that are especially susceptible to lahars. These include the United States. Mexico, Ecuador, Japan, Indonesia and the Philippines. Mount Rainier in the US, Ruapehu in New Zealand and Galunggung in Indonesia are presently considered high risk locations for lahars.

Some modern day lahars have captured the publics attention due to the violent volcanic catastrophe. The 1953 Tangiwai (New Zealand) lahar swallowed a Christmas Eve passenger train taking 151 lives with it. The 1980 Mount St Helens (United States) captivated the attention of the public as the lahar flowed and covered formerly beautiful forest lands. The 1985 Armero (Colombia) devoured the town and its 23,000 inhabitants. The lahars and the destruction of the past need to be the guideline for the future.

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