An eruption is likely to be preceded by days to months or more of small earthquakes centered beneath the volcano, by subtle deformation of the volcano, and by increases in volcanic gas emissions and temperatures. Detection of these natural precursors can allow communities to go to heightened levels of alert and take basic precautions against hazards. New eruptions of Mount Rainier will most likely start with steam and ash explosions at the summit, and progress to the effusion of a small lava flow or the disintigration of steeply sloping lava flows as avalanches of hot rock and gas called a pyroclastic flow.
Either type of eruption will probably create lahars that can reach heavily populated areas. Weak, hydrothermally altered rocks remain at high elevation on the volcano's west flank, and some of this material could be dislodged by earthquakes during an eruptive period. We cannot rule out the possibility that altered material could collapse due to its own weakness, without a triggering eruption or earthquake. Many people live in the river valleys downstream from Mount Rainier, so these eruptive and collapse events pose substantial hazards that are the reason for concerted scientific studies and cooperative measures with officials.
Lahars, a type of volcanic mudflow, are what make Rainier such a threat to nearby cities. These mudflows are often triggered by the heat of volcanic events that melt snow and glaciers. The rushing water collects dirt, rocks, debris, and speed as it travels through valleys down a mountain, annihilating whatever lies in its path. The destructive power of a lahar was demonstrated in , when the town of Armero was struck by one from the Nevado del Ruiz stratovolcano, wiping out the town and resulting in the deaths of over 20, people.
This event, referred to as the Osceola Mudflow , shows just how far lahars would go if a similar eruption were to occur. Geologists use this and other evidence to assess future hazard potential and to map zones in river valleys heading on Mount Rainier that could be inundated by future lahars.
Not all valleys would necessarily be affected during a given eruption or large landslide, nor would all lahars in a valley be large enough to extend to hazard-zone boundaries. Lahar hazard zones mapped by the USGS are being used to guide the development of hazard-area regulations in comprehensive land-use plans by counties and cities that lie at the foot of Mount Rainier.
A detection component consists of arrays of monitors that record the ground vibrations of a lahar. Computerized evaluation of data assesses the presence of a flowing lahar and issues an automatic alert to emergency-management agencies. Emergency managers can then initiate appropriate response measures. City, county, and State agencies design and maintain notification procedures, evacuation routes, and public-education programs. If a large lahar were generated in the upper Puyallup River valley without the precursors that typically herald volcanic unrest and eruption, it could arrive at the City of Orting as little as 40 minutes after the initial warning is sounded.
Time could be short, and successful mitigation will depend on effective notification of people at risk, public understanding of the hazard, and prompt response by citizens.
This system for automatic detection and notification of a lahar reduces-but does not eliminate-risk in the lahar pathways. Volcanoes often show signs of unrest, such as increased seismicity earthquakes and emission of volcanic gases and swelling of the volcano, days to months in advance of an eruption.
When unrest is detected, scientists will notify emergency-management officials and increase monitoring efforts. The plan describes the responsibilities of agencies and how they will communicate with each other and the public during a volcanic crisis.
Know the signs of debris flows and lahars. Experience from around the world shows that moving to high ground off the valley floor is the only way to ensure safety during a lahar. When hiking in valleys on the slopes of Mount Rainier during late summer or during intense rainfall, be alert for the signs of an approaching debris flow-ground shaking and roaring sound-and move up the valley wall to higher ground. The same is true for lahars, but, because they affect much larger areas, people need to move out of threatened areas before lahars get close.
Lahars are almost always preceded by volcanic unrest, so in most instances there will be time to warn people when there is an increased risk. Driedger and William E. Mount Rainier Mount Rainier: The flat floor of the Puyallup River valley near Orting, Washington, is formed by deposits of the year-old Electron lahar, which surged down from Mount Rainier in background.
Majestic Mount Rainier soars almost 3 miles 14, feet above sea level and looms over the expanding suburbs of Seattle and Tacoma, Washington. Each year almost two million visitors come to Mount Rainier National Park to admire the volcano and its glaciers , alpine meadows, and forested ridges.
However, the volcano's beauty is deceptive. It has been the source of countless eruptions and volcanic mudflows lahars that have surged down valleys on its flanks and buried broad areas now densely populated. To help people live more safely with the volcano, USGS scientists are working closely with local communities, emergency managers, and the National Park Service.
Lahar at Nevado del Ruiz Armero, Colombia, was battered in by lahars generated by an eruption of glacier-clad Nevado del Ruiz volcano. Mount Rainier Lahar and Flows Map Mount Rainier hazard zones: This map shows areas that could be affected by debris flows, lahars, lava flows, and pyroclastic flows from Mount Rainier if events similar in size to past events occurred today.
How to prepare for a lahar or other volcano hazard: Learn: Determine whether you live, work, or go to school in a lahar hazard zone. Learn about all volcanic processes that could affect your community. Plan: Develop an emergency plan with your family so that you are prepared for natural hazards and emergencies. Inquire: Ask public officials to advise you about how to respond during any emergency.
Osceola Mudflow Lahar Deposit Studying old lahar deposits: Geologists study the deposits of past lahars to assess potential future hazards. Spatter Cones Mount St. Find Other Topics on Geology. Maps Volcanoes World Maps.
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