四级复习资料大全阅读(29)_大学英语阅读

四级复习资料大全阅读(29)

　　The point where the seismic activity occurs is the epicentre, where the earthquake is strongest. But it doesnt always end there; seismic waves travel out from the epicentre, sometimes creating widespread destruction as they pass.

　　Volcanoes

　　Without doubt, erupting volcanoes are the most awesome and terrifying sights in nature. In fact, their untamed destructive firepower has shaped and influenced many ancient cultures from Pompeii, to Japan.

　　Its estimated that one in ten of the Worlds population live within danger range of volcanoes. According to the Smithsonian Institute, there are 1511 active volcanoes across the globe, and many more dormant ones that could recharge at any moment.

　　When tectonic plates collide，like earthquakes, volcanoes form at weak-points in the Earths crust, known as fault-lines.

　　When two tectonic plates collide, the event can provide the catalyst for volcanic activity. As one section slides on top of the other, the one beneath is pushed down into the mantle. Water trapped in the crust can cause reactions within the mantle. Why? Well, its thought that when the water mixes with the mantle, it lowers the mantles melting point, and the solid mantle melts to form a liquid, known as magma.

　　Under Increasing Pressure

　　Since liquid rock is less dense than solid rock, magma begins to rise through the Earths crust. It forces its way up, melting surrounding rock and increasing the amount of magma.