In order to protect public and private property from being destroyed by lava flows, various plans and actual attempts have been

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问题     In order to protect public and private property from being destroyed by lava flows, various plans and actual attempts have been made in the past on volcanoes to stop or divert lava flows, including Mount Etna, Sicily, Italy; Kilauea and Mauna Loa volcanoes, Hawaii, and Eldfell volcano, Heimaey, Vestmannaeyjar, Iceland. The lava-cooling operations on Heimaey, Iceland, were, however, the most extensive ever attempted, and the two excellent accounts of the operations that were published in Icelandic by a geophysicist and two engineers are translated into English in this open-file report. BirgirJonsson also published a report on the use of dikes to divert lava flows; he mentioned past attempts in Italy, Japan, Iceland, Samoa, and Hawaii, but devoted most of his paper to presenting a case study of the 1973 eruption on Heimaey.

    The village of Vestmannaeyjar, in the far northern country of Iceland, is as bright and clean and up-to-date as any American or Canadian suburb. It is located on the island of Heimaey, just off the mainland. One January night in 1973, however, householders were shocked from their sleep. In some backyard red-hot liquid was spurting from the ground. Flaming skyrockets shot up and over the houses. The island’ s volcano, Helgafell, silent for seven thousand years, was violently erupting!
    Luckily, the island’s fishing fleet was in port, and within twenty-four hours almost everyone was ferried to the mainland. But then the agony of the island began in earnest. As in a nightmare, fountains of burning lava spurted three hundred feet high. Black, baseball-size cinders rained down. An evil-smelling, eye-burning, throat-searing cloud of smoke and gas erupted into the air, and a river of lava flowed down the mountain. The constant shriek of escaping steam was punctuated by ear-splitting explosions.
    As time went on, the once pleasant village of Vestmannaeyjar took on a weird aspect. Its street lamps still burning against the long Arctic night, the town lay under a thick blanket of cinders. All that could be seen above the ten-foot black drifts were the tips of street signs. Some houses had collapsed under the weight of cinders; others had burst into flames as the heat ignited their oil storage tanks. Lighting the whole lurid scene, fire continued to shoot from the mouth of the looming volcano.
    The eruption continued for six months. Scientists and reporters arrived from around the world to observe the awesome natural event. But the town did not die that easily. In July, when the eruption ceased, the people of Heimaey Island returned to assess the chances of rebuilding their homes and lives. They found tons of ash covering the ground. The Icelanders are a tough people, however, accustomed to the strange and violent nature of their Arctic land. They dug out their homes. They even used the cinders to build new roads and airport runways. Now the new homes of Heimaey are warmed from water pipes heated by molten lava.
    Because of the success of the Icelanders in their massive lava-cooling operations during the 1973 eruption of Eldfell volcano within the town of Vestmannaeyjar, on the island of Heimaey, in the Vestmannaeyjar archipelago, Iceland, a scientist decided that English translations of two relevant reports by Icelandic scientists and engineers on the lava-cooling operations would be useful to volcanically active regions, where access to water (river, lake, or ocean) could provide the basis for lava-cooling operations.  
How long had the island’ s volcano been inactive?

选项

答案Seven thousand years.

解析 文章第二段最后一句提到,岛上沉寂了七千年的黑尔加费尔火山正在猛烈地喷发。因此,这座火山沉寂了七千年。由此可知本题答案。
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