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【听力文摘】夏威夷超级火山

2011-09-28    来源:普特编辑部    【      美国外教 在线口语培训

Hawaii’s Next Island

Look at a map of Hawaii and you’ll see volcanic islands strung out like pearls on a necklace. The biggest–and the youngest–is Hawaii, in the south-east corner.

As the islands stretch away to the north-west they become older and more worn. While Hawaii is about a million years old, the extinct volcano of Kauai on the north-west end is five times older.

The Hawaiian islands were formed by what geologists call “hot spot” volcanos. These occur where hot magma from the Earth’s liquid mantle is steadily forced through the Earth’s crust.

Hot spots can last for millions of years, staying in the same place while the plates of the Earth’s crust move gradually overhead.

The plates of the Earth’s crust move at uneven speeds, so when the plate moves slowly, this allows a tremendous volcano to build up. That’s why we get a string of separate volcanos, rather than a continuous line.

This is exactly what’s happened with the Hawaiian islands. The hot spot stayed in the same place, pushing up a string of volcanos as the Earth’s crust moved over it.

Because of this, the volcano on north-west Kauai is old and extinct, while the volcanos on Hawaii’s south-east edge are the most active in the world.

The Hawaiian hot spot is now located about seventeen miles off the south-east coast of Hawaii. There’s no new island there, but there is a huge, underwater volcano, rising almost three miles above the ocean floor.

This new volcano will break the ocean’s surface in about fifty thousand years, giving us our next Hawaiian island.


 

下一个夏威夷超级火山

随便翻看一张夏威夷的地图,你会发现夏威夷的火山岛分布得就像串在一条项链上的一颗颗珍珠一样。其中威力最大——也是最年轻的火山,当属夏威夷东南角的夏威夷火山。

随着岛屿不断地向西北方向延伸,各大火山变得越来越陈旧,破败。虽然说夏威夷已历经了一百万年的岁月,但是,在西北端考艾岛的死火山却已是其五倍了。

夏威夷群岛是由地质学家们所称的“火山热点”组成。“火山热点”处在由地幔(又称软流层,很可能是岩浆的发源地)产生的炽热的岩浆不断地被喷出地壳的地方。

“火山热点”能持续活动数百万年。就算是地壳板块活动而渐渐居于其上,“火山热点”也一直都不会改变地方。

地壳板块不是以均匀速度移动的,因而,当板块运动较慢时,一个巨大的火山就可“趁机”形成。这就是为什么火山是一个个单独的火山,而不是一片连续不断的火山了。

在夏威夷群岛上也就是如此。“火山热点”一直在某个地方,在地壳板块对其作用时形成了一座又一座的火山。

因此,西北端考艾岛上的火山都是很老的死火山,然而,位于夏威夷东南边的火山却是世界上活动最频繁的活火山。

而今,夏威夷的“火山热点”位于夏威夷东海岸约17英里的地方。目前,那里还没有新的岛屿形成,但是那里有一座很大很大的海底火山,高出海底足有三英里高。

在未来的五万年里,这座新火山将会使海底地壳断裂,创造出下一个夏威夷火山。

 



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