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英語(yǔ)聽(tīng)力文摘576 希臘不總是人間天堂!

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Greek Island Shows Signs Of Volcanic Unrest

Fira is a typical Greek city overlooking the Aegean Sea. Sitting atop a twelve hundred foot cliff on Santorini Island, it’s an ideal vacation spot. But this island wasn’t always a paradise. Thirty five hundred years ago, it was the site of one of the largest volcanic eruptions in historic times.

The Santorini volcano blew up with very little warning, causing a massive tsunami that destroyed coastal towns around the Mediterranean. The volcano collapsed to form what looks like a collection of small islands, but the islands are actually part of the rim of its four mile wide sunken caldera.

The volcano’s long slumber, followed by such a sudden and massive eruption, was a puzzle to scientists. Why does a volcano sit dormant for thousands of years and then suddenly erupt? Scientists think they have found a clue in layers of crystal rock.

Magnesium is one element present in the volcano’s different rock layers. Since it diffuses slowly through crystalline rock, scientists can calculate rock ages by how much magnesium is present.

Scientists found that almost all of the crystal layers on Santorini were deposited just before the eruption. That meant that several cubic miles of hot magna rose from the depths of the volcano very rapidly. The magma melted and mixed with the rocks just below the surface immediately before the massive explosion. The volcano that had been sleeping for thousands of years woke in the blink of an eye.

Researchers don’t know what caused such a large volume of magma to rise so quickly, but their findings may give scientists a clue to help predict the next big eruption. GPS measurements show that the rim of Santorini is deforming right now, indicating that more magma may be on the rise.

  希臘島嶼顯示火山活動(dòng)跡象

  菲拉是一座典型的希臘城市,坐落在圣托里尼島1200英寸高的懸崖之上,俯瞰愛(ài)琴海,是一處理想的度假勝地。但這座島嶼在過(guò)去并非一直是人間天堂。3500年前,這里發(fā)生了歷史上最大規(guī)模之一的火上噴發(fā)。

  圣托里尼火山在爆發(fā)之前幾乎沒(méi)有任何征兆,爆發(fā)后引起一場(chǎng)巨大的海嘯,摧毀了地中海沿岸的城鎮(zhèn)。接著火山發(fā)生塌陷,形成了如今這一系列小島。這些島嶼事實(shí)上是沉入海水中的四英里寬火山口的一部分。

  圣托里尼火山在長(zhǎng)期沉寂后突然發(fā)生大規(guī)模的爆發(fā),這一現(xiàn)象令科學(xué)家們感到費(fèi)解。為何一座火山幾千年來(lái)一直處于休眠狀態(tài),卻會(huì)突然爆發(fā)呢?科學(xué)家們認(rèn)為他們已在結(jié)晶巖層中找到了線索。

  鎂元素存在于火山的不同巖層中。由于它在結(jié)晶巖層中擴(kuò)散緩慢,因此科學(xué)家們可以通過(guò)檢測(cè)鎂元素含量來(lái)計(jì)算巖層的年齡。

  科學(xué)家們發(fā)現(xiàn),圣托里尼島上幾乎所有的結(jié)晶巖層均恰好在火山爆發(fā)之前沉積下來(lái)。這意味著,體積達(dá)數(shù)立方英里的火熱巖漿從火山深處迅速?lài)姲l(fā)出,在大規(guī)?;鹕奖l(fā)之前立即將地表下的巖石融化,并與之混合。已沉睡千年的火山就這樣在眨眼之間蘇醒了。

  研究人員不清楚是什么原因?qū)е氯绱硕鄮r漿的快速?lài)姲l(fā),但他們的研究發(fā)現(xiàn)也許可以為科學(xué)家們預(yù)測(cè)下一次的大爆發(fā)提供線索。GPS測(cè)量顯示,圣托里尼火山口邊緣正在變形,這預(yù)示著更多的巖漿可能正蓄勢(shì)待發(fā)。

 

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