首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Growth Secrets Of Alaska’s Mysterious Field of Lakes The thousands of oval lakes that dot Alaska’s North Slope are some of t
Growth Secrets Of Alaska’s Mysterious Field of Lakes The thousands of oval lakes that dot Alaska’s North Slope are some of t
admin
2013-07-11
69
问题
Growth Secrets Of Alaska’s Mysterious Field of Lakes
The thousands of oval lakes that dot Alaska’s North Slope are some of the fastest-growing lakes on the planet. Ranging in size from puddles to more than 15 miles in length, the lakes have expanded at rates up to 15 feet per year, year in and year out for thousands of years. The lakes are shaped like elongated eggs with the skinny ends pointing northwest.
How the lakes grow so fast, why they’re oriented in the same direction and what gives them their odd shape have puzzled geologists for decades. The field of lakes covers an area twice the size of Massachusetts, and the lakes are unusual enough to have their own name: oriented thaw lakes. "Lakes come in all sizes and shapes, but they’re rarely oriented in the same direction," said Jon Pelletier, an assistant professor of geosciences at The University of Arizona in Tucson.
Now Pelletier has proposed a new expla-nation for the orientation, shape and speed of growth of oriented thaw lakes. The lakes’ unusual characteristics result from seasonal slumping of the banks when the permafrost thaws abruptly, he said. The lakes grow when rapid warming melts a lake’s frozen bank, and the soggy soil loses its strength and slides into the water. Such lakes are found in the permafrost zone in Alaska, northern Canada and northern Russia.
Previous explanations for the water bodies’ shape and orientation invoked wind-driven lake circulation and erosion by waves. On Alaska’s North Slope, the prevailing winds blow perpendicular to the long axis of the lakes. According to the traditional explanation, such winds set up currents within the lakes that erode the banks, particularly at the lakes’ ends. Such currents would erode coarse grained, sandy soils faster than fine-grained clay soils.
According to Pelletier, one key ingredient for oriented thaw lakes is permafrost the special mixture of soil and ice that forms the surface of the land in the Far North. On the north coast of Alaska and at similar latitudes throughout the world, the top, or active, layer of the permafrost melts at some point in the summer and refreezes again in the fall.
If the temperature warms gradually, the ice portion of the permafrost melts slowly, allowing the water to drain out of the soil and leave relatively firm sand or sediment behind. However, if an early heat wave melts the permafrost’s ice rapidly, the result is a soggy, unstable soil. When such rapidly thawed permafrost is part of the vertical bank of a lake, the bank slumps into the water, enlarging the lake. More of the bank collapses if the soil is fine-grained, rather than sandy.
Another ingredient in Pelletier’s explanation is a long, gentle slope. Because Alaska’s oriented lakes are embedded in a gently sloping landscape, the downhill end of a lake always has a shorter bank. According to Pelletier’s Computer model, shorter banks melt more and have bigger slumps. Therefore when the lake experiences thaw slumping, Pelletier’s model says the lake grows more in the downhill direction than it does uphill, generating the lakes’ characteristic elongated egg shape.
The most mysterious part about Alaska’s lakes is______.
选项
A、their fast-growing speed
B、their variety in size
C、their elongated-egg shape
D、their uniform orientation
答案
D
解析
本题考查推理引申题。四个选项在第一段都有涉及,而且也都是阿拉斯加湖泊群的特点。但是第二段末句指出,湖泊的形状和大小不一是正常现象,但走向相同却很少见。因此[D]才是其最神秘的一点。
转载请注明原文地址:https://kaotiyun.com/show/Ov4O777K
0
专业英语八级
相关试题推荐
Atsometimeinyourlifeyoumayhaveastrongdesiretodosomethingstrangeorterrible.However,chancesarethatyoudo
Advertisinghasgrowntobeanindustryworthmanybillionsofdollarsacrosstheworld.Almostallpublicspacehassomeadvert
Hollywoodisinthestateof______.
WilliamwontheBattleofHastings,later,on______,hewascrownedKingofEngland.
EveryEnglishmanisbornwithacertainmiraculouspowerthatmakeshimthemasteroftheworld.(1)______Whenhewantsa
Whatiscorporateculture?Atitsmostbasic,it’sdescribedlikethe(1)______personalityofanorganization,orsimplyas"ho
Shynessisconsideredapersonalitytrait,notapsychologicalconditionordisorder,andithasvaryingdegrees.Butsevereshy
A、nowsheisthehighestpaidactressinHollywoodB、itchangespeople’sperceptionofwomeninHollywoodC、ithelpshergainse
A、NewYorkB、LosAngelesC、SeattleD、DallasDB洛杉矶是美国第二大城市,尤以Hollywood的电影工业等闻名,C西雅图是美国西北部最大的城市,D达拉斯是美国的石油工业中心。
随机试题
“百日维新”期间,光绪皇帝实施的改革措施有哪些?
A.出生时B.2岁C.3岁D.5~6岁E.7岁面高度的生长量完成了成人的73%的年龄是
耐药金黄色葡萄球菌感染可选用
桩基施工过程中如出现异常情况,可由施工单位自行处理,正常施工。()
增压器按驱动增压器的动力不同,可分为()。
假设其他条件不变,当各资产间的相关系数为负时,风险分散效果较好。()
青岛位于山东半岛,在山东处于领先的经济地位,对全国的影响力较大。作为一个沿海的旅游城市,酒店业比较发达,数量众多。但整体管理水平并不高,很多酒店目前还都处于手工操作的阶段。部分酒店管理者对酒店管理系统持有排斥态度,认为没有必要在这块进行投资。但随着市场环境
一位社会学家对两组青少年做了研究,第一组成员每周看有暴力内容的影视的时间平均不少于8小时:第二组则不多于1小时。结果发现第一组成员中举止粗鲁者所占的比例要远高于第二组。因此,此研究表明,多看有暴力内容的影视容易导致青少年举止粗鲁。下列哪项最能削弱上述结论?
表格控件的数据源可以是()。
在窗体上画多个控件,其中有一个名称为Text1的文本框,影响Text1的Tab顺序的属性是
最新回复
(
0
)