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
Geology Why are some glaciers called surging glaciers?
Geology Why are some glaciers called surging glaciers?
admin
2012-01-14
33
问题
Geology
Why are some glaciers called surging glaciers?
You might expect that heavy snowfall is the main requirement for the formation of a glacier. But if you stop and think about it, you’ll realize there are lots of areas of the world that receive huge amounts of snow but have no glaciers. Snowfall alone isn’t enough. For a glacier to form, the snow can’t melt. It has to be conserved. In the extremely cold Arctic and Antarctic, there are large areas that receive minimal precipitation and actually qualify as desert. Although there’s little snow, there are massive ice sheets because the snow that does fall is conserved and transformed into ice.
Of course, lots of places do get large amounts of snow, and they do have glaciers ... high mountains, for example. In high mountains where the climate is humid and cold, snowfall is frequent. Above the snowline, the annual snowfall exceeds the annual melting, so snow builds up. The accumulation is thickest in the hollows at the heads of valleys, because these locations are relatively high and cool, and are protected from sun and wind.
As snow accumulates in a hollow, it’s gradually converted to ice. First, the fragile snow crystals break as they’re compressed by the weight of more snow settling on top of them. There’s some melting and refreezing because of compaction, earth heat, and seasonal temperature fluctuations. So, the snow crystals are broken, then they’re wetted by meltwater, and refrozen, over and over again.
Gradually, over time, the snowflakes change into grains. They become rounded and granular, like the grains of coarse sugar. There are pockets of air between the grains, connecting the grains to one another. This old snow, called "firn," is generally created after one complete winter-summer cycle.
Firn is actually bits of ice. The firn begins to re-crystallize, and eventually, it combines and crystallizes into solid ice—a glacier. What happens is, the small grains coalesce to form large interlocking crystals of ice, with air trapped as bubbles inside the crystals. In the end, it’s pure ice, with all the air squeezed out. The flow of the glacier down the mountain contributes to crystal growth, as the movement helps to compress the air out.
As the hollow in the valley head fills with snow turning to ice, the hollow enlarges, and the rock walls are carved out by shifting ice. As new snow is added, the lower part of the snow-and-ice mass bulges out, kind of like a mud pie. As the mass continues to bulge, part of the ice moves over the edge of the hollow and starts moving down the valley. Large glaciers usually move faster than small ones. Also, the movement is faster in the summer, when more meltwater is present beneath and around the ice mass to lubricate it and buoy it up.
Most valley glaciers move at a rate of... oh ... between a few inches and a few feet a day. But some glaciers—called surging glaciers—can travel as much as 300 feet a day. There are at least 200 of these surging glaciers in Alaska and the Northwest Territories. The surging is caused by a number of conditions, like ... oh ... sudden adjustment to an increase in the snow load.on top, or, more likely, an increase in the production of meltwater due to a rise in temperature. Glaciers that have more meltwater are better lubricated and tend to move faster than drier ones. In very cold climates, glaciers are quite dry because of the lack of melting. The amount of water is slight, so the glacier does not slide as quickly.
In warmer climates, glaciers are better lubricated with meltwater. They also cause more erosion, more carving out of the valley floor. This is because during the melt-freeze cycle, parts of the glacier freeze to the bottom and sides of the valley, and then, as the ice moves on, large chunks of glacier pluck out rock. So you can see why glaciers in warmer climates have a greater impact on the landscape than those in very cold climates.
选项
A、They move much faster than other glaciers.
B、They form during one winter-summer cycle.
C、They continuously change form as they move.
D、They add a lot of silt to mountain rivers.
答案
A
解析
The professor says Most valley glaciers move at a rate of... oh ... between a few inches and a few feet a day. But some glaciers-called surging glaciers- can travel as much as 300 feet a day. (2.2)
转载请注明原文地址:https://kaotiyun.com/show/HTyO777K
0
托福(TOEFL)
相关试题推荐
BIRDMIGRATIONABirdshavemanyuniquedesignfeaturesthatenablethemtoperformsuchamazingfeatsofendurance.Theyareeq
BIRDMIGRATIONABirdshavemanyuniquedesignfeaturesthatenablethemtoperformsuchamazingfeatsofendurance.Theyareeq
Youshouldspendabout20minutesonQuestions14-26whicharebasedonReadingPassage2below.California’sAgeofMegafiresD
Lookatthefollowingopinionsordeeds(Questions9-13)andthelistofpeoplebelow.Matcheachopinionordeedwiththecorre
Theusespeoplemakeofsocialnetworkingwebsitesareunlikelytoincreaseinthefuture.
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
Thestartoftheautomobile’shistorywentallthewaybackto1769whenautomobilesrunningonthesteamenginewereinventeda
ThePearlA.Thepearlhasalwayshadaspecialstatusintherichandpowerfulallthroughthehistory.Forinstance,women
CompletethenotesbelowWriteONEWORDONLYforeachanswer.TheGherkinBuildingCommissionedby:【L31】______firmcalledFoste
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
随机试题
华为任正非:商业思想家美国《时代》周刊2006年有一期评选出2005年度影响世界的100位名人,华为科技公司总裁任正非是“商界巨子”中唯一入选的中国人。同时入选的还有美国苹果计算机公司董事长兼首席执行官乔布斯、传媒大亨默多克、俄罗斯石油巨头阿布拉
地面工程施工中水泥混凝土垫层的厚度不应小于()mm。
干粉输送管道采用螺纹连接时,安装后的螺纹根部有()扣外露螺纹,连接处外部清理干净并做防腐处理。
()是一种一次性的工作,必须在明确规定的时间内,由为此专门组织起来的人员完成。
在中原经济区发展规划中,以郑州为中心,形成中原城市群“紧密层”的“半小时交通圈”、辐射全省省辖市的“1小时交通圈”和连接周边省会城市的“2小时交通圈”,非常有利于推动国内旅游的发展。不在“2小时交通圈”的省会城市为()
近年来大学生到农村当村官,有村民反映说大学生经验不足,还有的大学生也说自己觉得不适应,不好开展工作,说说你的看法。
(2012年真题)甲、乙分别为国有公司总经理和副总经理,二人挪用单位1000万元公款给张三从事期货交易,收受并平分了张三的30万元回扣。司法机关在查处甲、乙挪用公款案件时,甲主动交代自己收受了张三15万元回扣,并揭发乙也收受了15万元回扣。本案中(
(2008年试题,22)设n元线性方程组Ax=b,其中(I)证明行列式|A|=(n+1)an;(Ⅱ)a为何值时,方程组有唯一解?求x1;(Ⅲ)a为何值时,方程组有无穷多解?求通解.
目前,100BASE-T有()、100BASE-TX与100BAST-FX3种传输介质标准。
将数据项“Student”添加到名称为List1的列表框中,并使其成为列表框第一项的语句为()。
最新回复
(
0
)