Deep under the Earth’s surface, it’

Deep under the Earth’s surface, it’s so hot that even rock melts. Sometimes this molten rock, called “magma”, is pushed up to the surface.【小题1】And the opening or vent that lets the lava out is a volcano.A volcano may explode violently, throwing out rocks for miles around.【小题2】Some volcanoes release clouds of poisonous gas or huge clouds of ash. Volcanoes can even do all these things underwater.Most volcanoes have been around for a very long time. Many haven’t erupted for years and have cooled off. Volcanoes that are not going to erupt again are called “dead volcanoes”. Some volcanoes still give off smoke. These “sleeping volcanoes” may “wake up” one day and erupt again. 【小题3】 But one day in AD 79 it suddenly woke up. Its eruption threw out hot ash and rocky fragments (碎片) that buried the city of Pompeii. A hot mud-flow buried nearby Herculaneum. Because the remains are so well preserved, the area has been named a World Heritage site.But not all volcanoes are destructive. When a volcano throws out vast amounts of lava and debris (岩屑), it piles up into a mountain.【小题4】Other volcanoes help provide heat and energy. Many Icelandic homes get their hot water from springs heated by volcanic steam.【小题5】 Plants grow very well in the rich soil left by volcanoes. And valuable gems, such as diamonds, can sometimes be found in the rocks that are thrown out by volcanoes.