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 What is the lecture mainly about? Click on two answers.
Geology What is the lecture mainly about? Click on two answers.
admin
2012-01-14
70
问题
Geology
What is the lecture mainly about? Click on two answers.
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、The world’s largest glaciers
B、How glaciers are created
C、The movement of glaciers
D、Why glaciers are melting
答案
BC
解析
The professor discusses how glaciers are created: You might expect that heavy snowfall is the main requirement for the formation of a glacier; For a glacier to form, the snow can’t melt. The professor also discusses the movement of glaciers: ...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...; Most valley glaciers move at a rate of... (2.1)
转载请注明原文地址:https://kaotiyun.com/show/JTyO777K
0
托福(TOEFL)
相关试题推荐
Choosethecorrectletter,A,B,CorD.Writeyouranswersinboxes31-33onyouranswersheet.Thecombinationofchangeshas
Youshouldspendabout20minutesonQuestions1-13whicharebasedonReadingPassage1below.AlfredNobelThemanbehindthe
Accordingtothewriter,whatproblemsarefacedwhenregulatingvideogames?
LivingDunesWhenyouthinkofasanddune,youprobablypictureabarrenpileoflifelesssand.Butsanddunesareactuallydyn
LivingDunesWhenyouthinkofasanddune,youprobablypictureabarrenpileoflifelesssand.Butsanddunesareactuallydyn
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
TheConceptofChildhoodinWesternCountriesThehistoryofchildhoodhasbeenaheatedtopicinsocialhistorysincetheh
WhichpiechartshowstheagesoftheAsianstudentssurveyed?WhichpiechartshowsthemainreasonsAsianstudentswantedto
Thelecturersaysthatanessayislike______toaspecificquestion.Considertheeffectsofdivorceonchildren.
Thelecturersaysthatanessayislike______toaspecificquestion.【36】
随机试题
装配要点包括部件装配和总装配。()
认为艺术产生的根本动力和原因是人类实践活动的艺术起源学说是______。()
家畜受精时,精子必须首先穿过
患者3年来经常心悸、气短。检查:心尖搏动稍向左下移位,心浊音界稍向左下扩大,心尖部听诊可闻及3/6级以上粗糙的收缩期吹风样杂音及舒张期隆隆样杂音。应首先考虑的是()
企业要想提高边际贡献总额,可采取的措施有()。
ABC公司研制成功一种新产品,现在需要决定是否大规模投产,有关资料如下:资料一:产品单价为每台3万元,销售量预计每年可以达到10000台,付现成本每年25000万元。新产品将在2019年1月1日投产,假设营业现金净流量发生在每年年底。
在对经营者集中进行反垄断审查并作出是否禁止该集中的决定过程中,反垄断执法机构应主要考虑一些经济因素。下列各项中,属于该类经济因素的有()。(2011年)
答案中的金额用人民币万元表示,有小数点的保留两位小数,小数点后四舍五入。甲股份有限公司(以下简称甲公司)系20×7年新设立的家电类企业,假定ABC会计师事务所的A和B注册会计师负责对其2×10年度财务报表进行审计,在接受该项业务以后先对甲公司进行了解,然
在1858年签订的中俄()中,俄国割占中国东北外兴安岭以南、黑龙江以北地区60多万平方公里的领土。
简述气质与性格的区别。
最新回复
(
0
)