高中英语Unit5 The power of nature文章 Volcano人教版选修六

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2024年7月10日发(作者：)

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What Is A Volcano?

The word "volcano" es from the little island of Vulcano in the Mediterranean Sea

off Sicily. Centuries ago, the people living in this area believed that Vulcano was the

chimney of the forge of Vulcan -- the blacksmith of the Roman gods. They thought that

the hot lava fragments and clouds of dust erupting form Vulcano came from Vulcan's

forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars,

the god of war. In Polynesia the people attributed eruptive activity to the beautiful but

wrathful Pele, Goddess of Volcanoes, whenever she was angry or spiteful. Today we

know that volcanic eruptions are not super-natural but can be studied and interpreted by

scientists.

The Nature of Volcanoes

Volcanoes are mountains, but they are very different from other mountains; they

are not formed by folding and crumpling or by uplift and erosion. Instead, volcanoes are

built by the accumulation of their own eruptive products -- lava, bombs (crusted over

lava blobs), ashflows, and tephra (airborne ash and dust). A volcano is most monly a

conical hill or mountain built around a vent that connects with reservoirs of molten rock

below the surface of the Earth. The term volcano also refers to the opening or vent

through which the molten rock and associated gases are expelled.

Driven by buoyancy and gas pressure the molten rock,which is lighter than the

surrounding solid rock, forces its way upward and my ultimately break through zones of

weaknesses in the Earth's crust. If so, an eruption begins, and the molten rock may pour

from the vent as nonexplosive lava flows, or it may shoot violently into the air as dense

clouds of lava fragments. Larger fragments fall back around the vent, and accumulations

of fallback fragments may move downslope as ash flows under the force of gravity.

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Some of the finer ejected materials may be carried by the wind only to fall to the ground

many miles away. The finest ash particles may be injected miles into the atmosphere

and carried many times around the world by stratospheric winds before settling out.

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