Geology And Geophysics

Lahar



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Lahars cause volcanic activity to be as deadly as it is. At rapid speeds, these muddy streams of water, similar to the consistency of wet concrete, carry volcanic debris including ash, cinder, and large boulders down the slopes of volcanoes or river valleys, merciless. People, buildings, vehicles, roads, bridges, along with all other man-made objects and natural elements have no chance to contest its fury as they are buried and crushed by their monumentous force. Surviving a lahar, when in its path, is nearly if not completely impossible as it is fluid while moving, and as it slows and stops, it turns to a solid, meaning that everything in its way is intermixed into a sea of concrete.

Although lahars generally come about due to an occurence of intense rainfall during or after a volcanic eruption, they can also occur due to a volcanic eruption itself, the rapid melting of ice and snow as a result of a sudden and intense heat wave, a certain type of disruption in a crater lake, or the basal melting of glacial ice near flows of lava.

Lahars have been responsible for a great many deaths over the years in areas near volcanoes. Although not all lahars are major events, some throughout history have been especially tragic. For example, in 1953, 151 people met their fate when a lahar caused a Christmas Eve express train to leave its track and take a dive into the Whangaehu River. Three decades later, in 1985, a lahar formed after the eruption of the Nevado del Ruiz volcano in Columbia and buried the village of Armero and surrounding areas, killing more than 23,000 men, women, and children. Six years later, in 1991, Mt. Pinatubo in the Philippines erupted amidst a raging typhoon which ignited a monstrous lahar that took the lives of over 1500 people, while the eruption itself was responsible for only six lives.

Living in an area surrounding a volcano is dangerous. Although it can be predicted where lahars can occur and where they may possibly flow, they are ticking time bombs, and you never know for sure when they may be triggered, making them especially lethal. It's been predicted that one of the next catostrophic lahars could occur in the Pacific northwest area of the United States near one of the volcanoes in the Cascade Mountains. The areas surrounding Mt. Rainier seem to be primarily suseptible, with its periodic melting of glacial ice and potential for eruptions. Due to this prediction, this volcano is monitored closely and plans are in place to warn the local population and bring them to safety before disaster strikes.

Several techniques have been used to try and prevent or at least slow lahars including the building of retention basins, tunnels, alternate channels, and large concrete structures. Some of these methods have worked better than others and some work with less intense lahars, but fail to halt the most intense lahars. In areas suseptible to lahars, it's extremely important to establish warning systems to alert people in a lahar's path using seismometers to detect the signal of a lahar as it begins to move down a valley or guages that collect water and warn people when the formation of a lahar is likely. Additionally, it's important that evacuation plans are drawn up and drills are held to assure that in the event of a real lahar that as many people as possible could be saved.

Volcanoes themselves are dangerous and are responsible for deaths, however resulting lahars, usually occurring with little or no warning, are a great deal more deadly.

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