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Lahars vary in speed. Small lahars less than a few metres wide and several centimetres deep may flow a few metres per second. 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]
The word lahar is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows. Nearly all of Earth's largest, most destructive debris flows are lahars that originate on volcanoes. An example is the lahar that inundated the city of Armero, Colombia.
Lahars (from a Javanese term for volcanic mudflows) are a mixture of volcanic debris and water. 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]
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.
The high temperatures can burn flammable materials in the flow's path, including wood, vegetation, and buildings. Alternately, when an eruption has contact with snow, crater lakes, or wet soil in large amounts, water mixing into the flow can create lahars, [4] which pose significant known risks worldwide.
Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of volcanoes) and jökulhlaups (outbursts from under glaciers or icecaps). [6] A statutory definition of "flood-related mudslide" appears in the United States' National Flood Insurance Act of 1968, as amended, codified at 42 USC Sections 4001 and ...
The lahars can coat objects, wash objects away and can knock objects down by their force. Lahars, debris flows and mudflows that travel into a river or stream run the potential for crowding the waterway, forcing the water to flow outward and causing a flood. The volcanic matter could also pollute the water, making it unsafe to drink. [citation ...
Subglacial eruptions, those of ice-covered volcanoes, result in the interaction of magma with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcanic areas, including Iceland, Alaska, and parts of the Andes.