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VOICE ONE:
This is Faith Lapidus.
VOICE TWO:
And this is Doug Johnson with EXPLORATIONS in VOA SpecialEnglish. Today we tell about Yellowstone National Park. It is one ofthe most beautiful national parks in the United States. However, anancient and extremely violent volcano created the great beauty ofYellowstone. The ancient volcano that formed Yellowstone is notdead. It is only sleeping. And some experts say it could become verydangerous in the future.
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Yellowstone National Park is inthe western state of Wyoming. It is one of the most unusual placesin the world. Extremely hot water shoots out of the ground inseveral hundred places. Small lakes contain water that is so hot itis dangerous to come too close.
Visitors can watch bubbles coming up through boiling, hot mud.They can see rocks that were once liquid and have cooled intostrange shapes.
Yellowstone is built on an ancient volcano. A lake of hot liquidrock is about six kilometers under the park. This lake is aboutsixty-five kilometers wide. Experts say this lake is under hugeamounts of pressure. The pressure and heat cause hot water to shootout of the ground and mud to boil at Yellowstone.
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The Yellowstone volcano has often been called a super volcanobecause it is so big. Scientists believe major volcanic activity inthe Yellowstone area began about two million years ago. Thisactivity created violent explosions and built mountains and valleys.Experts believe this super volcano had three major explosions callederuptions. Each of those three eruptions may have been more powerfulthan any in recorded history.
Each eruption threw out millions of tons of ash and rock. Thelast eruption was so huge it covered much of North America with ash.Some of this ash traveled high into the atmosphere and was carriedby strong winds around the world.
This cloud of volcanic ash circled the Earth many times. Itaffected the climate by limiting the amount of sunlight that reachedEarth's lower atmosphere and surface. This last eruption formed themountains and valleys that visitors can see today in Yellowstone.
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When a volcano erupts, a huge amount of material explodes out ofthe volcano. This leaves a giant circular hole in the ground, calleda caldera. Experts have known for many years that Yellowstone wasformed by volcanic activity. However they could not find thecaldera. Many experts searched a huge area in and around YellowstonePark looking for the remains of the caldera. A few years ago, theNational Aeronautics and Space Agency tested new satellite cameras.They offered Yellowstone Park officials photographs of the parktaken from space.
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A national park expert wasextremely surprised when he looked at the photographs taken fromspace. He immediately saw the caldera they had been searching for.The photographs showed that Yellowstone National Park is thecaldera. The caldera is about seventy kilometers long and thirtykilometers wide.
In fact, the park is a system of calderas formed within the pastsixteen million years. Experts now believe that as many fifteen ortwenty smaller eruptions also formed calderas.
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Scientists know the volcanic heart of Yellowstone is deep withinthe Earth. This area is called a hot spot. It is only one of a fewsuch places on Earth.
Extreme pressure deep in the Earth forces liquid rock up throughthe hot spot to the lake of hot material that is below the surface.This causes the extreme heat that is found in Yellowstone.
Scientists also know the Yellowstone hot spot is linked to theactivity of the North American plate. The North American plate isone of several plates that make up the surface of the Earth. Theseplates move a few centimeters each year. The hot spot does not move.Very often the action between the hot spots and the plate causesgreat earthquakes as plates move against each other. The platesoften split apart. And often after earthquakes, the hot spot forcesliquid rock to the surface. This has not happened for severalthousand years.
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The Yellowstone hot spot has been linked with the North Americanplate for as long as seventeen million years. At many differenttimes, the hot spot has caused a kind of liquid rock called basaltto explode to the surface.
This basalt rock from the Yellowstone hot spot can be found inthe western states of Washington, Oregon, California, Nevada andIdaho. Evidence of this basalt rock can be found in an area as largeas three hundred twenty-two thousand square kilometers.
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Yellowstone National Park is the oldest national park in theworld. About three million people visit it each year. Its greatnatural beauty has made it one of the most popular nationalparks.Most visitors like to see "Old Faithful", the world's mostfamous geyser. A geyser shoots hot water high into the air. Thereare more than three hundred geysers in Yellowstone.
Old Faithful is not the biggest orthe most beautiful geyser. But it is the most popular. Visitorsgather around Old Faithful before each eruption. Experts at the parkare able to predict when these will happen. The average time betweeneruptions is about ninety minutes. Old Faithful shoots water anaverage of forty meters into the air. This eruption lasts betweentwo and five minutes. Old Faithful releases up to about thirtythousand liters of water into the air each time.
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The hot spot deep under the ground produces geysers like OldFaithful. Old Faithful is evidence of the volcanic activity atYellowstone. But will the Yellowstone volcano erupt again? Mostexperts think the answer is yes. But no one knows when. The mostrecent of the three extremely powerful eruptions was about sixhundred fifty thousand years ago.
Experts say at least thirty smaller volcanic eruptions have takenplace at Yellowstone. Some of these were perhaps as big as thenineteen ninety-one eruption at Mount Pinatubo in the Philippines.Several are believed to have been much larger. The most recent ofthese smaller eruptions took place about seventy thousand years ago.
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Volcano experts say it is extremely difficult to tell whenYellowstone might become an active volcano again. However,earthquakes near a volcano are usually good evidence that a volcanomight become active again. For example, Mount Saint Helens in thenorthwestern state of Washington exploded in nineteen eighty.Several earthquakes took place near the volcano before that time. Onthe morning that it exploded, Mount Saint Helens experienced anearthquake of five point one on the Richter scale.
Yellowstone National Park experiences several thousandearthquakes each year. Most are very small. They cannot be felt.They can only be measured by scientific instruments. However, inAugust of nineteen fifty-nine, an earthquake at Yellowstone measuredseven point five on the Richter scale. Twenty-eight people werekilled.
It was one of the strongest earthquakes ever recorded in theUnited States. But Yellowstone's sleeping giant volcano did noterupt.
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In two thousand one, the United States Geological Survey,Yellowstone National Park and the University of Utah signed anagreement.
That agreement established the Yellowstone Volcano Observatory.Under the agreement, the park, the Geological Survey and theuniversity are responsible for improving efforts to study thevolcanic system of Yellowstone.
The observatory uses information from many different instrumentson the ground and from satellites to study the volcano. Theinformation will help officials decided if Yellowstone's hugevolcano is becoming a danger. Then they could warn the publicquickly if necessary.
Experts at the observatory say Yellowstone represents some dangerto the public. It always has. However, its natural beauty also makesit a treasure that could not be possible without the sleeping giantvolcano that is under Yellowstone National Park.
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VOICE ONE:
This program was written by Paul Thompson. It was produced byMario Ritter. This is Doug Johnson.
VOICE TWO:
And this is Faith Lapidus. Join us again next week for anotherEXPLORATIONS program in VOA Special English.