Mount St. Helens-2.pdf
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- 2. Mount St. Helens,also known as Lawetlat'la to the indigenous Cowlitz people, is an active stratovolcano located in Skamania County, Washington. It lies 52 miles northeast of Portland, Oregon, and 98 miles south of Seattle. Mount St. Helens takes its English name from that of the British diplomat Lord St Helens, a friend of explorer George Vancouver who surveyed the area in the late 18th century. The volcano is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire. STRATOVOLCANO STRATOVOLCANO
- 3. PLATE BOUNDARY MAP Asan Eastern remant of the Pacific Plate, the Juan da fuca plate,has subducted beneath continental North America the Cascade volcanic chain has formed. The Mt.St.Helens volcano has been active for around 40,000 years but the now damaged cone we see today has formed over the last 2,200 years - The largest explosion of Mt.St.helens happened 3500 years ago which produced 13 times more material than in 1980. The volcano is highly explosive and erupts in the Plinian style like Vesuvius. Sudden violent explosions are accompanied by towering clouds of hot ash, dust and rocks thrown high into atmosphere. Pyroclastic flows and volcanic mud flows called Lahars flow down the mountain at speed and consume the surrounding landscape. lavas from basalt to andesites have been erupted forming layers of ash and lava.
- 4. 2 3 4 1 DIAGRAM EXPLAINED Mt StHelens is on the plate boundary between Juan de Fuca and the North American plates, the boundary is also a part of the Ring of Fire. The Juan de Fuca plate is an oceanic plate and the North American plate is a continental plate. The two plates became a destructive plate boundary. When a continental plate meets an oceanic plate. The oceanic plate (Juan de Fuca) descended underneath the continental plate (North American plate) as it is denser. When the oceanic plate descends further and further under the plate reaching past the lithosphere, it reaches the asthenosphere part of the upper mantle, the plate begins to melt because of the friction between the two plates. Once the plate has melted it turns into extremely hot, liquid rock, which is known as magma. The magma then rises through the gaps of the continental plate and when it reaches the surface it forms a volcano. This process goes on for hundreds of thousands of years, as more years go by more magma rises. In this case when the magma rose, gases couldn’t escape causing the magma to build more pressure, which creates a big volcanic explosion/eruption.
- 5. The Mount St.Helens major eruption of May 18, 1980 remains the deadliest and most economically destructive volcanic event in U.S. history. Fifty- seven people were killed; 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed.Autopsies indicated that most of Mount St. Helens' vicitims died by asphyxiation from inhaling hot volcanic ash, and some by thermal and other injuries. On May 18 1980 Mt.St.Helens produced an enormous lateral blast which obliterated everything for 20 miles north of the volcano. The summit decreased from 2930m to 2550m and a gaping crater 1.5km wide was created. Effects on People
- 6. Short Term LongTerm The eruption damaged roughly 230 square miles of land around the volcano, according to the USDA Forest Service. It destroyed 158 miles of highway, and 15 miles or railways, the USGS reported. Washington state worked to remove about 900,000 tons of ash from highways and roads. Within 6 years after the 1980 eruption, most lakes had returned to conditions typical of undisturbed Cascade Range lakes. In sharp contrast, terrestrial ecosystems, covered with nutrient-poor volcanic ash and rock, had greatly diminished biological productivity after the 1980 eruption. The lateral blast, debris avalanche, mudflows, and flooding caused extensive damage to land and civil works. All buildings and related manmade structures in the vicinity of Spirit Lake were buried. More than 200 houses and cabins were destroyed and many more were damaged in Skamania and Cowlitz Counties, leaving many people homeless. Many Lodges closed down which had a massive impact on the economy because there was nowhere for tourists to stay. Many tens of thousands of acres of prime forest, as well as recreational sites, bridges, roads, and trails, were destroyed or heavily damaged. More than 185 miles of highways and roads and 15 miles of railways were destroyed or extensively damaged. The Ash settled 15cm deep so when it rained, it produced alot of mud flows and made it hard for trees and other crops to grow Effects on the Environment
- 7. Benefits of living neara volcano tourists are attracted to the volcano, which increases money to the local economy Volcanoes can provide people with many benefits such as: volcanic rock and ash provide fertile land geothermal energy can be harnessed, minerals are contained in lava, eg diamonds - these can be mined to make money which results in a higher crop yield for farmers. which provides cheaper electricity for locals
- 8. IMMEDIATE RESPONSES IMMEDIATE RESPONSES ThePortland District of the Corps of Engineers responded immediately to the unfolding crisis. It turned its attention first to floods and to restoring navigability. Its neighboring districts in Seattle and Walla Walla conducted damage assessments in the affected regions. Corps personnel raised levees along the Cowlitz. They cleared debris from the Columbia and employed four hopper dredges and several contracted pipeline dredges to create an emergency navigation channel that allowed over 75 percent of the normal shipping traffic to resume by mid-June. With the initial emergency response successfully completed, the Corps turned to address mid-term problems such as flood threats from impounded waters and the continued sedimentation and debris flows into the area’s rivers. The volcano had disrupted the entire hydrological flow of the basin and, between June and November 1980, the Corps instituted a number of response measures. Corps and contractor personnel worked around the clock to clear debris and dredge navigation channels in the Cowlitz and lower Toutle Rivers, removing thirty-five million cubic yards of sediment and restoring the pre-disaster flow rate of the Cowlitz. The Corps also raised levees in the region to protect against potential flooding.
- 9. LONGER TERM RESPONSES LONGERTERM RESPONSES The eruption of Mount St. Helens has influenced volcanology in many ways, and the next step in this evolution is the National Volcano Early Warning System, or NVEWS. In March 2019, USGS was authorized by Congress to develop and implement NVEWS to more fully monitor volcanoes and to warn and protect citizens of the United States from danger caused by volcanic activity. When NVEWS is fully implemented, all hazardous U.S. volcanoes will be monitored at levels consistent with the threat they pose to communities, infrastructure and aviation. Pro-active early warning of a potential eruption is key to minimizing loss of life and economic disruption by increasing the time that emergency managers can initiate mitigation measures, improve evacuation alerts and better position resources for recovery. Earliest detection of eruption precursors with multiple instrument types allows for more accurate forecasts of hazardous eruptive activity needed by land managers and the aviation sector.