Secrets of Avalanches and Lightning_资讯

　　　just as we humans can be poisoned so the land we live on is also liable to poisoning. in china today, farmland contaminated with heavy metals accounts for 20% of the country’s total arable land. the annual grain loss resulting from this pollution of nature has no reached 10 million tons with a total value of around 1.2 billion us dollars. scientists all over the world are now working on viable ways to clean up such polluted land.

　　phytoremediation is a method of cleaning up polluted soil using plants that are best able to absorb pollutants, in particular, heavy metals. the metals absorbed in the plants can then be recycled for use.

　　in march 2004, researchers of the chinese academy of sciences developed the world’s first ever arsenic-polluted soil restoration technique and set up a pilot phytoremediation project. their research proved that the ciliate desert grass of the fern family, which is extensively distributed in southern china, is readily able to absorb arsenic. the arsenic content in the leaves of this plant is several hundred thousand times of that of other plants.

　　as spring comes people’s memory of the winter snow begins to fade. however, it is at this time that the accumulated snow on high mountain slopes is most likely to cause a white terror, or avalanche.

　　there are two kinds of avalanches. one is caused by powdered fresh snow while the other is caused by densely pressed hard snow accumulated over several years. the latter is likely to occur when the weather begins to warm.

　　because they are a common natural disaster, avalanches pose the greatest danger to mountain lovers. each year, about 30 snow skiers are killed by avalanches.

　　to find out more about avalanches, american scientists arrived at an avalanche-prone snow mountain in march of 2004 and, using dynamite, triggered off several avalanches.

　　200 tons of heavy snow rolled down from the mountaintop at a speed of 160 kilometers per hour. researchers found that this fast-rolling mass of snow was as hard as rocks. a real avalanche is much more fatal than people usually think. scientists hope they can find an effective way to predict when and where an avalanche will occur. until that time, however, all people can do is be cautious whenever they are near a snow-covered mountain.

　　like flowers in spring and snow in winter, a timely rain can also be a source of inspiration.

　　no matter how terrifying a thunderbolt may look like, in the eyes of scientists, thunder and lightening is an inevitable natural phenomenon. there are about 2,000 thunderstorms around the globe every day, and there is lightning almost every second.

　　in a french laboratory, scientists have created artificial lightning using an electricity generator in order to find out which part of a given structure was mostly likely to be struck by lightning. the subject of the experiment was a high-voltage power transmission tower. at one end of the lab, a powerful thunderbolt was created with temperatures as high as 30,000 degrees celsius. the lightning strike was strong enough to leave marks on the tower structure.

　　a global monitoring system could precisely predict the time and place of major lightning strikes. finding out which parts of a building or a structure are most vulnerable to lightning strikes could help people take proper precautions well in advance.

　　no weather forecasts can ever be 100% accurate, but it is an undeniable fact that scientists are leading us increasingly away from disasters.