Реферат: Mt St Helens Essay Research Paper hat
Mt. St. Helens Essay, Research Paper
hat Causes A Volcano?
It was once thought that volcanic eruptions were the result of water moving into highly heated area of the earth. That not true any more. More recently, with the better understanding of the movement of the earth’s crust plates, known as plate tectonics, has been accepted as generating the energy that causes a volcanic eruption. (Microsoft, Encarta) Volcanoes form at the site of 2 kind of plate boundaries. The convergent plate plunges under another divergent plate. The lower plate is drawn down to a depth at which it becomes molten, or a liquid hot magma. This magma is always flowing, like a river’s current. But sometimes the crust and the upper mantle are not always even, if rising magma gets though a gap, crack, or weakness between the 2 plates a volcanic eruption forms. Scientists call these “plate margins.”
Mt. St. Helens was considered to be in a long state of dormancy, one that lasted 123 years. Usually after a long state of dormancy the eruption is very violent. Scientists were aware of activity before the eruption but did not have any documented experience at that point to predict the exact magnitude of the eruption.
At 3:48 p.m. March 20, 1980, seismographs in Seattle, Newport and Washington all registered an earthquake 20 miles north of Mt. St. Helens. The news was largely ignored in the press, but it did catch the attention of the United States Geographical Service Volcanologists. Geologists said it was just a “burp”. But one week later on March 27 the volcano made itself known with an explosion of ash and steam. It is one of the greatest volcanic explosions ever recorded in North America! The pressure from the magma causes extensive fissures and a bulge on the north side of the peak.
On May 18th an earthquake caused a gigantic landslide on the north side of the mountain. The slope gave away an avalanche followed with a side blast that caused mudflows, pyroclastic flows and floods. That buried the valleys as far as 17 miles away. Along with the avalanche came the blast of gas and ash that rose more than 12 miles high! The ash fell as far east as Montana. Also six miles of levee were built to help and protect the nearby communities and other forests. The U.S. Army Corps of Engineers built 10 more miles of temporary levees near Lexington, Castle Rock, Kelso and Longview. The first response to the eruption was to make sure that people and communities were safe.
continuous dredging of the Cowlitz and Columbia Rivers prevent flooding.
The debris avalanche deposited 5.5 billion cubic yards of rock and ice into the Toutle River Valley. That is a lot of debris. “If every person in the world today was asked to help haul it away in five-gallon buckets, each person would have to make 15 trips before it was all gone!” ( From Web Page) That’s an almost limitless source of debris material filling in the Cowlitz and Columbia Rivers. Since 1980, the United States Government spent over 1 billion dollars on the recovery of Mount St. Helens. More then half of that funding has been spent by the Corps for designing, and contracting projects to correct the problems with the river. This work has improved the safety of the communities around the river.
“I remember the very moment that Mount St. Helens exploded on May 18th. I was in bed, and there was this huge boom. And I have to tell you, I was 160 miles away from Mount St. Helens, but the force of the blast reached us — at least audibly — and, you know, the windows in my house shook.
And I fell out of bed. I had a — I knew that this was probably the Mount St. Helens eruption, because this was something that we had expected for months. And ran down to the radio station I was working at the time, and you know, looked at the wire copy. And there was one word at the beginning of the wire story, and it was “awesome.”
The top half of Mount St. Helens — it had been a nice, you know, cone-shaped peak with a lot of snow on it at that time of year — was just gone. And pouring out of the gaping hole in the mountain was this just constant flow — mushrooming flow of ash and rock and smoke.
It was rising — it was 65,000 feet in the sky that this would — plume was rising. And then, of course, it was going off to the east. And ash was raining down both to the north and east on that particular day, eventually reaching, you know, as far as Helena, Montana. I mean, this ash went for hundreds of miles. It turned daylight into midnight all along where that ash cloud went.”
Mr. Berkes later commented on how quickly the signs of life returned, even when they were using snow plows to remove the ash from the roads. “Scientists were pointing out, you know, to us signs of small rodents, other animals kind of appearing. And there were little blades of grass coming up through ash. But, you know, for the scientists to get up there they had to kind of plow roads through the ash. And this is ash that was, you know, 10, 15 feet by the side of the road. It was — and the road was on ash. They just sort of dug a road in there.
It was the most incredible thing. You’re used to seeing that with snow in the mountains. Imagine it being just a gray, volcanic ash.”
The explosion of Mt. Saint Helens was one of the most dramatic and powerful natural events in the history of North America. Being an active volcano, the story of Mt. Saint Helens is not over yet. We might see another eruption yet in our lifetime!
The Mt. St. Helens Web Site