.. the shortest outburst and cause the most damage and destruction, Plinian eruptions that send out ash that covers hundreds of square miles are called ultra Plinian. There have been 19 Plinian eruptions in history. Plinian Eruptions The plume height is more that 25 km or more than 15.5 miles high. The Volcanic Explosivity Index rating is VEI 5 and the violence of eruption is categorized as Paroxysmal.

The volume is 668,900 cubic miles. Plinian eruptions are named after Pliny the Elder who watched the Mount Vesuvius eruption in A.D. 79. Plinian eruptions are sometimes called Vesuvian eruptions. They blast out tons of materials in a blast that is the most powerful force on earth.

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The explosion tears apart the mountain and the hot gas filled clouds that form set off lightening and thunderstorms. So much ash is released in Plinian eruptions that it is carried by the wind around the entire planet. The ash forms a layer around the Earth, blocking out some of the suns energy and brings cooler temperatures to the Earth. Mudflows Mudflows are very dangerous. As they melt the ice and snowcap on the mountain, they rush down the mountain's side taking everything with them.

They become very thick and cement like and bury everything in their pathway. The mudflows from MSH raced down the north face of the mountain at ninety miles per hour. At the bottom of the mountain it slowed down too thirty miles per hour. The mudflows was forty- four to sixty-six feet deep. When the water drained away over three feet of mud was left behind.

The mudflows not only destroyed all the trees and plants, but also killed thousands of animals including deer, elk and beers. Different sources say that 57 or 62 people were killed form the eruption of MSH including the volcanologist David Johnston, a member of the U.S. Geological Survey team at MSH. The lateral blasts, avalanche, mudflows and flooding caused huge amounts of damage to the land and city. All buildings and structures in the area of Spirit Lake were buried. More than 200 houses were destroyed, leaving many people homeless.

Tens of thousands of acres of forest, recreational areas, bridges, roads and trails were destroyed. Wildlife suffered huge losses. The Washington state Department of Game estimated that 7,000 big game animals (beer, elk and deer) died in the area, as did all birds and small mammals. Volcanoes can be very destructive but in the long run they are helpful. Because the ash s rich in potassium and phosphorus it helps to grow very healthy plants and crops.

Volcanic heat energizes most of the world's thermal areas and hot springs. Volcanoes are also responsible for creating much of the mineral wealth on earth. The hot water underground removes minerals from the magma dn deposits them in the earth's crust. They form veins of silver, gold, zinc, copper and lead. Because of the plate movements, some minerals that were deposited on ancient sea floors are now accessible to mining. Diamonds are also created by volcanic activity and are fund in eroded volcanic pipes or tubes.

The May 18 eruption wiped out most large forms of life on the north side of the mountain. Life began to reemerge in the form of bacteria, fungi, weeds, seeds, insects, spiders and pocket gophers. Bt the end of summer 1981, life was returning to the volcano. Volcanic eruptions are important to life on Earth because they add gasses to the atmosphere and water to the ocean. Volcanoes also build land mass.

Floods of lava have built large area of continents like the Columbia Plateau in the Pacific Northwest. Volcanoes also make soil as the ash, pumice and lava break down. This mixed with plant and animal remains makes very rich soil. In 1980, MSH erupted six more time, usually blowing ash into the air and causing pumice to slide down the side of the mountain. In June and August, the lava that came out from the top was thick enough to finally form a new dome. This dome was destroyed only to be formed again in October.

After this, the eruptions only added to the size of the dome making it larger. What came out of MSH The erupting volcano sent out material and debris of all sizes. The term of all of this is tephra. the material that was blown out of the volcano was classified by its size. 0.1 inches or less =Ash 0.1-2.5 inches = Lapillo or little stones 2.5 inches and larger = Bombs and blocks Bombs are rocks that are soft when they are ejected while blocks are solid.

Both bombs and blocks can land miles away and fly at speeds of 1250 miles per hour. The blocks destroy whatever they land on while the bombs explode and burst into red hot liquid when they land. The earth has many volcanoes, the majority of them circling the Pacific Ocean. These volcanoes are known as the Ring of Fire. Scientists know that he volcanoes are in this formation because of the movement of the earth's crust.

There are over 400 active volcanoes in the world. They are found in weak places, or faults, in the Earth's crust, where two of the Earth's plates meet. Volcanoes and earthquakes occur in the same general area. Volcanoes seem to relieve some of the pressure of the Earth's mantle, so the earthquakes near them are milder. The band of Pesticides that activity is increasing. They use an instrument called a tiltmeter.

For weeks before MSH erupted, volcanologists were able to warn the people in the area that the rock around the volcano was active. The volcanologists measured the bulge of the volcano and the changes in the surface of the mountain. This helped to save many lives since they were able to let people evacuate the area. Current plate movement can be tracked directly by using ground-based or space-based geodetic measurements. Geodesy is the science of the size and shape of the earth. Ground-based measurements are taken with very precise surveying techniques using laser electronic instruments. Because plate motions are global in scale, they are measured by satellite based methods.

Among the techniques are VLBL (very long baseline interferometry) SLR (satellite laser ranging, and GPS (Global Positioning Systems) and are all based on technology developed for the military, aerospace, radio astronomy and satellite tracking. By monitoring the interaction of the Pacific Plate and the surrounding continental plates, scientists hope to learn more about the events leading up to earthquakes and volcanic eruptions in the Pacific Ring of Fire. Type of volcanoes. Not all volcanoes are the same shape even though they all begin as a crack or hole in the ground. As the volcanoes erupt, lava and ash build up forming the cone of the volcano.

If running lava from the volcano forms a gently sloping shape it is called a shield volcano. This lava can flow for many miles before it becomes cold. The eruption from this type of volcano is not very violent. If the lava is sticky and hardens quickly, the volcano will have steep sides. This is a composite cone or stratovolcano. MSH is a stratovolcano.

This type of eruption is the most violent. Stratovolcanoes are the most common type on earth. They are composed of almost equal amounts of ash and thick lava flows. This layering of ash and lava gave it the name of strato. The magma is extremely powerful and can form steep slopes of up to 35 degrees.

These volcanoes are not usually very big and occur along the subduction zone, mostly around the Pacific Ocean. Subduction is the process of one plate of the earth's crust moving under another plate. MSH is also called a composite volcano because it erupts both lava and ash. Dormant and Extinct Volcanoes If a volcano shows no signs of life for thousands of years it is thought to be extinct. If a volcano shows activity, even slight movement, it is dormant.

Volcanoes that have violent eruptions between long periods of no activity are usually stratovolcanoes. Volcanoes that are inactive and not expected to erupt in the near future are called dormant volcanoes. Volcanoes that are never expected to erupt again are called extinct. All of the volcanoes in the Cascade Range where MSH is found are dormant volcanoes. Approximately 50 or so volcanoes erupt every year.

The International Association of Volcanology defines active volcanoes as one that has erupted in historic times. Historic can mean 200 years in Hawaii or 3,000 years in the Mediterranean depending if there are historical records.