跟读练习: Volcanoes for Kids | A fun and engaging introduction to volcanoes for children - 通过视频学习英语口语

Volcanoes in this video we're going to learn about different types of volcanoes The earth is alive!

Not alive like you and me, but the earth is always moving and changing and never stays the same you may see it right before your very eyes or you may not see or feel it happen at all, but it's happening right now beneath our feet the earth is changing.

Let's explore some of the ways the earth changes. Run for your lives she's gonna blow!

It's a volcano! A volcano is a fracture or opening in the earth's crust through which magma escapes.

Deep in the bowels of the earth beneath the crusts are vast chambers of molten liquid rock we call magma.

Magma can slowly cool and become hardened or magma with trapped gases can flow and feed a volcano and rise to the surface of the earth.

When magma reaches the surface it becomes lava.

A volcano may be active or a volcano may be dormant, which means that it's only sleeping and may someday erupt or a volcano may be extinct which means that it was once active, but we'll probably never erupt again.

Let's explore three types of volcanoes.

Millions of years ago the islands of Hawaii emerged from the sea powered by erupting volcanoes the formation of the islands of Hawaii are examples of shield volcanoes.

Some of these volcanoes are active and continued to erupt, other volcanoes have been dormant for a million years. These volcanoes are massive in area and have gradual sloping sides.

The eruptions are like fountains and lava flows are very liquid. The Loihi volcano south of the big island of Hawaii is one actively erupting volcano under the sea.

Loihi is a seamount rising 10,000 feet from the floor of the Pacific Ocean and as it continues to erupt molten lava, it one day will become an island all its own in about a hundred thousand years.

Shield volcanoes are not as explosive as cinder cone volcanoes, a cinder cone volcano has straight steep sides.

In 1943, senior Pulido was working in his cornfield near the village of Parícutin, Mexico.

Pulido tells the story that as he and his family were working in the field that the earth began to tremble and shake and right before his very eyes the ground swelled to over six feet!

A fissure opened and grey ash and smoke poured into the air and the sound of a terrible hiss and the horrible smell of sulphur. Through the thick smoke Pulido could not find his family. He went back to the village and discovered they had arrived there safe and sound.

Through the days and weeks and years that followed the volcano would continue to grow to over 1,300 feet high or 396 point 24 metres.

Spewing hot smoke and ash into the air, everyone had to be evacuated and find another home as thick slow-moving lava would advance to the villages of Pparícutin and San Juan which were destroyed.

Can you imagine how awful that would be?

The Parícutin volcano has been very important to scientists as they have seen the birth and rise of a volcano and watch it become dormant.

And though a cinder cone volcano may be terrible it is no match for the spectacle of a volcano Which can be far more powerful, far more terrible, far more frightening and more explosive, of course we are talking about the Stratovolcano!

A Stratovolcano is characterized by gentle lower slopes gradually increasing too steep upper slopes. They are constructed of layers of hardened lava and volcanic ash and pumice.

Stratovolcanoes are known to have violent eruptions expelling fiery lava fragments through the air like bombs, toxic gases fill the air and massive plumes of ash clouds carry vast distances making aviation travel impossible.

These volcanoes are dangerous and deadly and though lava from these volcanoes flows slowly, it covers and burns and destroys everything in its path. In the Cascade Mountain Range of Southwest Washington State there rises many beautiful snow-covered peaks some of them are volcanoes.

One of these volcanic mounts is known as Mount St. Helens. It was no secret that Mount St. Helens had been an active volcano for hundreds maybe thousands of years and volcanologists scientists who study volcanoes had been studying St. Helens with their equipment watching and waiting for another perhaps major eruption it was possible that St. Helens would not erupt in their lifetime even with fancy equipment these things are difficult to predict. Then came the spring of 1980, for months tremors and earthquakes shook the ground on the North Face of Mount St. Helens a bulge began to form volcanologist, David a Johnston, was watching and measuring the growth of the Bulge with his lasers. On May 18th 1980 David called out over the radio, "this is it, this is it!" The caldera blew with supersonic fury.

Everything in the path of this massive eruption was wiped out for eight miles.

David A. Johnston was camped right in the path of the most destructive volcanic eruption in known US history.

250 homes, railways, bridges, highways, all gone. Could Mount St. Helens erupted again? Will you wait and see?

In the world there are nearly 1500 potentially active volcanoes, 169 are in the United States. Is there one near you?

Many volcanoes are located along the Pacific Rim, an area that reaches along South and North America along the Aleutian Islands of Alaska down the islands of Japan and the Philippines Indonesia New Zealand and the South Pacific.

This path in the Pacific Ocean is known as the Ring of Fire.

For millions of years our earth has been alive with erupting volcanoes in addition to those we've explored and among the most frightening and terribly destructive are Mount Vesuvius of Pompeii, Krakatoa in Indonesia and the volcanic complex in Iceland...

and deep underneath Yellowstone National Park lies enormous chambers of molten magma which one day may find its way to the surface and become the most massive supervolcano ever!

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