EROSIVE FLOW OF LAHAR: the Mount St. Helens eruption of 1982The famous 1980 eruption at Mt. St. Hele

EROSIVE FLOW OF LAHAR: the Mount St. Helens eruption of 1982The famous 1980 eruption at Mt. St. Helens, located in Washington state, blasted a caldera directly into the peak of the iconic volcano. However, this image shows the aftermath of a more minor volcanic explosion that occurred in the March of 1982.The visible black ash shown flowing down the mountain side is actually lahar. This mudflow is constituted primarily of pyroclastic material. Pyroclastic rocks, usually ejected from the volcano, are simply various forms of volcanic rock ranging in size. Mixed with water, this mass of pyroclastic material forms a massive tide of moving “cement”, capable of vast destruction and pollution. Lahar tends to obliterate obstacles in its path, known for carrying boulders as wide as 10 meters.As you can see, the path of this destructive lahar becomes larger in width as it nears the base of the volcano. Pyroclastic mud flow tends to do this, as the steady flow of lahar builds on itself by eroding further rock fragments on the mountainside. Gorges were found at the base of the volcano due to the lahar’s erosion, one gorge even dubbed the “mini-Grand Canyon.” Lahar is a common result in many stratovolcano eruptions due to its steep structure, intensity of explosion, and large quantity of loose rock debris. Lahar flow causes serious ecological harm to the surrounding environment. Think of it as a natural oil spill. The pyroclastic sediment infiltrates the areas water system and surrounding land, destroying plant and animal life. In this image, lahar is seen entering Spirit Lake, at bottom left. Following this explosion, lahar took over the North Fork Toutle River, and followed the natural river flow until lahar reached the Cowlitz River, an astounding 80 kilometers away! Lahar is an amazing observation of the natural world, yet is extremely harmful as it can destroy a diverse field of life, can block tributaries, and strip the land of its trees and soil.Sam J.Image Credit: Tom Casadevall, United States Geological SurveyReferences:http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_gallery_28.htmlhttp://volcanoes.usgs.gov/hazards/lahar/index.phphttp://www.icr.org/research/index/researchp_sa_r04/ -- source link

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