雅思阅读模拟题：The Spectacular Eruption of Mount St. Helens_雅思英语阅读

雅思阅读模拟题：The Spectacular Eruption of Mount St. Helens

　　G Afterwards, scientists were able to analyse the sequence of events. First, magmamolten rock-at temperatures above 2000oF. had surged into the volcano from the Earths mantle. The build-up was accompanied by an accumulation of gas, which increased as the mass of magma grew. It was the pressure inside the mountain that made it swell. Next, the rise in gas pressure caused a violent decompression. Which ejected the shattered summit like a cork from a shaken soda bottle. With the summit gone, the molten rock within was released in a jet of gas and fragmented magma, and lava welled from the crater.

　　H The effects of the Mount St. Helens eruption were catastrophic. Almost all the trees of the surrounding forest, mainly Douglas firs. were flattened. and their branches and bark ripped off by the shock wave of the explosion. Ash and mud spread over nearly 200 square miles of country. All the towns and settlements in the area were smothered in an even coating of ash. Volcanic ash silted up the Columbia River 35 miles away, reducing the debris that accumulated at the foot of the volcano reached a depth. in places, of 200 feet.

　　I The eruption of Mount St. Helens was one of the most closely observed and analysed in history. Because geologists had been expecting the event, they were able to amass vast amounts of technical data when it happened. Study of atmospheric particles formed as a result of the explosion showed that droplets of sulphuric acid, acting as a screen between the Sun and the Earths surface, caused a distinct drop in temperature. There is no doubt that the activity of Mount St. Helens and other volcanoes since 1980 has influenced our climate . Even so, it has been calculated that the quantity of dust ejected by Mount St. Helens - a quarter of a cubic mile- was negligible in comparison with that thrown out by earlier eruptions, such as that of Mount Katmai in Alaska in 1912 . The volcano is still active. Lava domes have formed inside the new crater, and have periodically burst. The threat of Mount St Helens lives on.