大学英语口语(四) Presentation文稿.doc

1-2 XUANXUANHello everyone, today I want to show you a part of how the earth was made, and mainly talk about Yellowstone.As continents shift and clash, volcanoes erupt, and glaciers grow and recede, the Earths crust is carved in countless fascinating ways, leaving a trail of geological mysteries behind. And one of the greatest is Yellowstone National Park in Wyoming. This is one of the worlds most geologically active places, shaken by up to 5000 earthquakes every year, and with more geysers and hot springs than in the rest of the world combined. Scientists studying Yellowstone are uncovering a violent past. Carved water, crushed by ancient glaciers and blasted by the biggest volcanic eruptions ever known on the planet. And even today, Yellowstone is one of the most dangerous places on Earth. 3 LAOCAOYellowstone is one of the most amazing places on Earth, and its unique. It contains some of Americas most stunning scenery and wildlife.YellowstoneistheworldsfirstnationalparkwhichisinthenorthwesterncornerofWyomingandoverlapsintoMontanaandIdaho. The park covers 3468 square miles, 63 miles north to south and 54 miles east to west. Its a very unusual geology that created the park.Hundreds of species of mammals, birds, fish and reptiles have been documented, including several that are either endangered or threatened. The vast forests and grasslands also include unique species of plants. Yellowstone Park is the largest and most famous megafauna location in the Continental United States. Grizzly Bears, wolves, and free-ranging herds of bison and elk live in the park.4-5 JIEOld Faithful is the star attraction of Yellowstone. Its one of the most predictable geographical features on Earth , erupting almost 91 minutes.Beneath Old Faithful is a rather complex plumbing system, filled with caverns and conduits and constrictions. Rainwater saturating the ground around the geyser slowly fills its underground reservoir. Hot rocks below ground heat the water under pressure for around 90 minutes. Suddenly some water spurts through a tiny, five inch wide crack in the rocks. This causes a drop in the pressure within the water chamber. In a instant, thousands of gallons of water are turned to steam and blasted up into the air. The gases come out from the geysers is the same mix that is found coming out of volcanoes. So gases are clear evidence that under the springs and geysers is a volcano. Yellowstone must be powered by the heat of the volcano. 6-10 WOPeople cant see a smoking volcano or a big steep volcanic crater. But where is the volcano? Scientists find out evidences to show us that Yellowstone is the super volcano.The black layer that geologists call “obsidian” is actually a type of glass. Its crucial evidence that the rocks and soil here came out of a volcano. Because of obsidian is forged when boiling hot ash and gas rapidly cool under great pressure. And thats just what happens when hot volcano clouds roll out across the landscape. There is one way that so much ash could have been blasted so very far away from its source. The eruption must have been larger, far larger than anything ever seen by man.Scientists now label it as a super eruption.The geologists have recreated what must have happened here one the day Yellowstone exploded.Incandescent avalanches of ash raced out of the park in all directions. They travelled at very high velocity, easily over 100 miles per hour, across the land surface and obliterating everything in its path. It was extremely hot when it arrived here as hot as 1500 degrees Fahrenheit.11-13 3PAOAll of the evidences about the size of the super eruption help solve the mystery of the missing volcano. Scientists realized that the super eruption was so enormous that it must have blown the volcano to pieces.The repeated hotspot explosions on land have made Yellowstone unique. Each of the earlier explosions blew the original mountains to pieces. Then the land smoothed over with later flows of more runny lava that was released from deep under the Earths crust.Multiple strands of evidence combine to reveal Yellowstones slumbering monster , the gigantic hotspot plume lying under the park.On the timescale that the geologists work to, a coming super eruptio