[ti:How Glaciers Can Burst and Cause Flooding] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.04]Indian rescuers searched on Monday for about 200 people missing [00:06.44]after part of a Himalayan glacier broke away Sunday and caused major flooding. [00:13.60]The flooding happened when part of the Nanda Devi glacier [00:18.24]broke off, releasing water trapped behind it. [00:22.56]The burst sent floodwater toward power plants and villages [00:27.44]in northern Uttarakhand state. [00:31.60]The floods destroyed bridges and broke dams. [00:35.28]Huge amounts of water, rock and building materials [00:39.60]flowed down a mountain valley. [00:42.76]At least 26 people are confirmed dead. [00:47.48]More than 2,000 military members, police officers and others [00:53.24]have been taking part in search-and-rescue operations. [00:57.32]Most of the missing were people working on two hydroelectric power plants. [01:04.48]The projects are part of government efforts [01:07.24]to develop the mountainous areas of Uttarakhand state. [01:12.24]The floodwaters rushed down the mountain and into other bodies of water. [01:17.84]Many villages along the Alaknanda and Dhauliganga rivers were evacuated. [01:26.24]The two rivers flow out of the Himalayan mountains [01:29.84]and later join with the Ganges River. [01:33.72]Videos on social media show the muddy, [01:37.32]gray floodwaters quickly flowing through a valley and into a dam, [01:42.96]and breaking it into pieces before continuing downstream. [01:48.32]Experts said the disaster could be linked to climate change. [01:52.96]A team of scientists was flown to the area Monday [01:57.24]to investigate what happened. [02:00.52]A glacier is a very large area of ice [02:04.04]that moves slowly down a mountainside [02:07.80]or valley or over a wide area of land. [02:10.72]Glaciers are made of closely formed layers of snow. [02:15.76]They move or flow because of gravity [02:19.16]and the softness of ice compared to rock. [02:23.96]A long and narrow piece of ice called a glacier's "tongue" [02:28.52]can extend hundreds of kilometers from its beginnings in high mountains. [02:34.12]The end of the tongue can advance or move backward [02:38.24]based on snowfall and melting. [02:41.76]Bodies of water called proglacial lakes are formed [02:46.20]after glaciers retreat, or move back. [02:49.64]Extra water or pressure -- or structural weakness [02:54.56]-- can cause both natural and manmade dams to burst. [02:59.80]This sends a mass of floodwater flowing down the rivers fed by the glacier. [03:06.72]It is not yet known what caused part of the Nanda Devi glacier to break off. [03:13.24]Seismic activity and a buildup of water pressure can cause glaciers to burst. [03:19.56]But climate change may be another cause. [03:23.36]High temperatures, combined with less snowfall, [03:27.16]can increase the speed of melting. [03:29.72]This causes water to rise to possibly dangerous levels. [03:36.04]Sarah Das is a scientist at Woods Hole Oceanographic Institute in Massachusetts. [03:43.68]She told The Associated Press, [03:46.76]"Most mountain glaciers around the world were much larger in the past [03:51.68]and have been melting and shrinking dramatically due to climate change..." [03:57.16]Sunday's disaster happened in the western part of the Himalayas. [04:02.44]The mountains form part of India's long northern border. [04:07.76]A 2010 information page published by the International Centre [04:12.68]for Integrated Mountain Development [04:15.20]called for more glacier observation in the Himalayas [04:19.08]to better understand "the real degree of glacial lake instability." [04:25.36]The area where the glacial burst took place experiences landslides and flooding. [04:32.24]Environmental experts have warned against building in the region. [04:37.36]I'm Ashley Thompson. [04:38.64]更多听力请访问51VOA.COM