Volcanoes happen where the earth's(40)____ is thin：lava，dust and gases(41)____ from beneath the can rise into a huge cone shape like a mountain and erupt，(42)____ they can be so violent(43)____ they just explode directly from the earth with no e are 1511(44)'____' volcanoes in the means that they may(45)____ be 1985 the Colombian volcano Nevado del Ruiz lava melted a glacier and sent tones of mud(46)____ the town ty thousand people ral disasters like volcanic eruptions are often regularly do not know when they(47)____ pen，or (48)____ where they will the future，scientists may be able to watch and predict(49)____ before they could(50)____ many lives.
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