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Large lahars hundreds of metres wide and tens of metres deep can flow several tens of metres per second (22 mph or more), much too fast for people to outrun. [9] On steep slopes, lahar speeds can exceed 200 kilometres per hour (120 mph). [9] A lahar can cause catastrophic destruction along a potential path of more than 300 kilometres (190 mi). [10]
The thicker and/or more fast-moving a lahar, the more potential to destroy things in its path, thus making it more dangerous than a slower and/or more diluted lahar. Lahars and mudflows can damage buildings, wildlife and cars and can prove difficult to escape once caught in them. The lahars can coat objects, wash objects away and can knock ...
A lahar is a volcanic mudflow or landslide. The 1953 Tangiwai disaster was caused by a lahar, as was the 1985 Armero tragedy in which the town of Armero was buried and an estimated 23,000 people were killed. [citation needed] Volcanoes rated at 8 (the highest level) on the volcanic explosivity index are known as supervolcanoes.
A powerful mudflow called a lahar is one of the most dangerous threats that can arise from a volcano.
Geologists consider Mount Rainier the most dangerous mountain in the United States, [2] and the USGS has estimated there is a one-in-seven chance of a catastrophic lahar at Mount Rainier occurring in the next 75 years. [3] Mount Rainier as seen from the High Cedars Golf Course in Orting, bordering the Carbon River
Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing a fast moving mudflow. Lahars are typically about 60% sediment and 40% water. [42] Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete. [43]
This meltwater mix means that subglacial eruptions often generate dangerous jökulhlaups and lahars. [57] The study of glaciovolcanism is still a relatively new field. Early accounts described the unusual flat-topped steep-sided volcanoes (called tuyas) in Iceland that were suggested to have formed from eruptions below ice.
As of 2018, Glacier Peak is classified as one of the 18 most dangerous volcanoes in the United States. [18] When lahars reach populated areas, they can bury structures and people. An example was the Armero tragedy at Nevado del Ruiz where 23,000 died from an enormous mudflow.