The Mississippi River itself completely changed character, developing sudden rapids and whirlpools(激流和漩涡). Several times it changed its course, and once, according to some observers, it actually appeared to run backwards. Few people were killed in the New Madrid earthquakes, probably simply because few people lived in the area in 1811; but the severity of the earthquakes was shown by the fact that the shock waves rang bells in church towers in Charleston, South Carolina, on the coast. Buildings shook in New York City, and clocks were stopped in Washington, D.C..
Scientists now know that America's two major faults are essentially different. The San Andreas is a horizontal(水平的)boundary between two major land masses that are slowly moving in opposite directions. California earthquakes result when the two masses make a sudden move.
The New Madrid fault, on the other hand, is a vertical fault; at some point, possibly hundreds of millions of years ago, rock was pushed up toward the surface, probably by volcanoes under the surface. Suddenly, the volcanoes cooled and the rock collapsed, leaving huge cracks. Even now, the rock continues to settle downwards, and sudden sinking motions cause earthquakes in the region. The fault itself, a large crack in this layer of rock, with dozens of other cracks that split off from it, extends from northeast Arkansas through Missouri and into southern Illinois.
Scientists who have studied the New Madrid fault say there have been numerous smaller quakes in the area since 1811; these smaller quakes indicate that larger ones are probably coming, but the scientists say they have no method of predicting when a large earthquake will occur.
【2014届高考英语一轮 Unit4 《Earthquakes》课后强化作业 新人教版必修1】相关文章:
★ 【北京专用】2014届高考英语一轮复习方案课时作业:选修6 Unit 2 Poems
★ 【浙江专用】2014届高考英语一轮复习课时作业(七)必修2Unit 2《The Olympic Games》
★ 北京市2014高考英语一轮复习 练习手册(34)选修7 Unit 4 Sharing(含解析)新人教版
★ 【北京专用】2014届高考英语一轮复习方案课时作业:必修2 Unit 5 Music
★ 【北京专用】2014届高考英语一轮复习方案课时作业:必修1 Unit 3 Travel journal
★ 【浙江专用】2014届高考英语一轮复习课时作业(十)必修2Unit 5《Music》
★ 四川省2016届高考英语一轮复习课时作业(34) Module 4 Music 外研版选修6
★ 2014届高考英语一轮复习课时作业(三十)必修5Module 6《Animals in Danger》(外研版)
★ 【北师大版】2014届高考英语一轮复习指导课时作业:Unit 9 A卷 Word版含解析
★ 2014届高考英语一轮复习课时作业(三十四)选修6Module 4《Music》(外研版)
最新
2017-04-24
2017-04-24
2017-04-24
2017-04-24
2017-04-21
2017-04-21