Deep within the earth, many miles down. It’s so hot that rocks melt and become magma. This magma collects in magma chambers and, if there is a weakness in the earth’s surface of rock, it pushes trough the weakness to become lava. The lava then flows slowly out the fissure, cools and becomes rock again. Over a period of many centuries as this process occurs again and again, a coneshaped volcano is formed. These volcanoes, called rift are not usually dangerous as the lava doesn’t move quickly and gives people time to get out the way.
There is a second type, of volcano, called subduction. That is far more dangerous. In this type the magma is particularly thick and the gasses, which would normally push to the surface, instead build up a great deal of pressure inside the earth.Finally they explode taking pieces of lava hundreds of feet into the air where it cools and falls to earth again as rock. Unfortunately these pieces of lava, called tephra, can range in size from tiny particles of ash to house-size boulders. These fiery explosions of tephra blast out of the volcano at speeds of over 200 miles an hour, destroying and killing everything in their paths.
Mount SaintHelens, Washington.
Mt. st. Helens, in the state of Washington, is just such a volcano. It had not erupted for 123 years and most people thought it was extinct. They were wrong.
After 123 years of silence, St. Helens showed her first signs of life on Thursday, March 20, 1980 with a 4.1 magnitude earthquake centered beneath the volcano. The earthquake was so wild that no one noticed. One weeklater, on March 27, the first puff of ash appeared. No one on the ground knew because the top of the mountain was in the cone. On March 30 there were 79 earthquakes under the mountain. On April 30 movement of magma was noted. The crater was now 1,500 feet wide. Explosions of ash, rock and ice chunks were almost a daily occurrence. Also, a large ‘bulge’ began to form on the north side of the mountain.The building pressure of hot gases and magma inside the mountain created the bulge, and it grew five feet a day.
May 18, 1980.
Sunday, May 18, 8:32 AM, a 5.1 magnitude earthquake struck one mile below the mountain. The ‘bulge’ could no longer withstand the pressure and an eruption occurred. Within moments, the largest landslides in recorded history swept down the mountain at speeds of 70 to 150miles an hour. It removed more than 1,300 feet from the summit and swept away almost the entire north side of the mountain. (The elevation of the mountain dropped from 9, 677 feet to its present day 8,363 feet.) it buried the Toutle River under an average of 150 feet of debris and in some areas up to 600 feet. The intense high pressure steam escaping from the rupture turned more than 70% of thesnow and, ice on the mountain to water. This mass of rock, ash, water and trees swept into Spirit Lake and down the Toutle river Valley at speeds in excess of 175 miles an hour.
The blast of gases flew across the valley at speeds up to 670 miles an hour and at a temperature of 660. Ash flowed out of the mountain at a temperature of 1,200, sterilizing the soil. When the eruption ended, 60 feet ofash covered the valley floor.
Meanwhile, the large portion of the landslide flowed down the Toutle river valley at speeds of 30 miles an hour, carrying rocks, trees and homes. Twenty-seven bridges were destroyed. A massive ash cloud grew to 80,000 feet in 15 minutes and reached New York in the three days. Fine ash circled the earth in 15 days and some of that ash was still circling the earth 20years later. Fifty-seven people died and of those, 21 bodies were never found. And then Mount back to sleep again.
En lo profundo de la tierra, a muchos kilómetros hacia abajo. Hace tanto calor que las piedras se funden y se convierten en magma. Este magma se acumula en cámaras de magma y, si hay una debilidad en la superficie de la tierra del rock, lo empuja a través de la...