首页
登录
职称英语
[img]2012q1/ct_etoefm_etoeflistz_0924_20121[/img] [br] Why does the professor me
[img]2012q1/ct_etoefm_etoeflistz_0924_20121[/img] [br] Why does the professor me
游客
2024-01-04
35
管理
问题
[br] Why does the professor mention permafrost in the Himalayas?
[Professor] (mate)
Q12 Today, we’ll be continuing with our theme of Arctic environments by discussing permafrost. I suppose you’ve come across this term before in your Earth science classes...but I’ll provide a quick definition anyway. Permafrost is ground--like rock or soil--that remains below zero degrees Celsius, or at zero, for at least two years. Zero degrees is, of course, the freezing point of water. Quite simply, the designation "permafrost" is based only on temperature.
Naturally, permafrost is commonly found in the higher latitudes, um, the ones nearer to the North and South Poles--places like Greenland, for example, which stretches all the way to 84 degrees north. But elsewhere in the Northern Hemisphere, um, most permafrost lies between about 60 and 68 degrees north. See, above that, it’s mainly the Arctic Ocean--no land. Q13 However, there’s also such a thing as "alpine" permafrost too, which can be present at much lower latitudes because it’s found at high altitudes, where the temperature is colder. Um, for example, this happens in the Himalayas, which are at a relatively low latitude. All totaled, permafrost accounts for about 24% of the planet’s landmass. Um, that’s about 22.79 million square kilometers of Earth’s exposed land.
Q15(Q)Q15(C) In many areas, permafrost is covered by a thin layer of soil that’s subject to thawing during warmer months and refreezing during the winter. This layer is known as the active layer. It’s usually about 0.6 to 4 meters thick; the depth depends a lot on the region and the conditions there. The characteristics of the permafrost layer itself can vary a little bit. Sometimes--if it’s composed of a nonporous material like bedrock--it won’t contain any ice at all. In other cases, it’ll contain up to 30% ice. Sometimes, permafrost may be covered by snow...and sometimes it isn’t. There’s a huge range of thickness, too. It may be just a meter in thickness, but at its thickest, permafrost can be 1,000 meters deep.
Q16 Interestingly enough, even though it’s relatively easy to classify permafrost -the ground surface has to be at zero degrees or less for two years, remember--it’s not so easy to exactly map its distribution. Common sense might tell us that permafrost should be found in places where the air temperature remains below freezing for most of the year, and that’s generally true...but, as it turns out, it’s not entirely that simple. Permafrost doesn’t always exist where air temperatures remain below freezing. Even beneath glaciers, where the air temperature is certainly very cold, there’s no guarantee that there’ll be permafrost.
Q12 Permafrost can be divided into two main categories. First, there’s discontinuous permafrost. This is the kind of permafrost you’d find in a region where the temperature barely stays below freezing throughout the year. If the annual surface temperature averages between 0 and -5 degrees Celsius, permafrost is only intermittent. It’s discontinuous. Now, since this makes for a broad category--I mean, in some places you could have just tiny little patches of permafrost, with most of the land unfrozen...and in other places there might be mainly permafrost with tiny patches of unfrozen ground. Q14 To account for these differences, the category of discontinuous permafrost is further divided into "extensive" discontinuous permafrost--where permafrost covers between half and ninety percent of the land--and "sporadic" permafrost...where permafrost covers less than half of the landscape. Um, the extensive discontinuous permafrost zone generally has temperatures that average between -2 degrees Celsius and -4 degrees Celsius. Q15(E) Sporadic permafrost makes up the warmer zones of discontinuous permafrost, where average temperatures are between zero and -2 degrees Celsius.
Q17 The other main category of permafrost...um, as opposed to discontinuous...the other category is continuous permafrost. By now, you must’ve guessed that this refers to places where there’s no unfrozen ground--where permafrost covers the entire landscape. Yep--you’re right. The boundary between continuous permafrost and discontinuous permafrost has actually moved north in recent years as a result of global warming. In the Yukon in Canada, the boundary has receded by about 100 kilometers in the past century or so. On the other hand, during the Earth’s last major period of glaciation, permafrost could be found a lot farther south than it is now. Back then, continuous permafrost extended as far south as Beijing, China. We’ll talk more about the last maior qlaciation period in our next class.
选项
A、To explain that certain conditions are necessary for the formation of permafrost.
B、To suggest that permafrost is more common than many people believe.
C、To emphasize the changes in permafrost that have occurred due to global warming.
D、To illustrate that alpine permafrost can be found at low latitudes.
答案
D
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3334016.html
相关试题推荐
NarratorListentoapartofadiscussioninabusinessclass.Theprofessor
NarratorListentoapartofadiscussioninabusinessclass.Theprofessor
BiologyCardiacMuscle[img]2012q1/ct_etoefm_etoeflistz_0107_20121[/img][br]Lis
BiologyCardiacMuscle[img]2012q1/ct_etoefm_etoeflistz_0107_20121[/img][br]Why
BiologyCardiacMuscle[img]2012q1/ct_etoefm_etoeflistz_0107_20121[/img][br]Why
Economics[img]2012q1/ct_etoefm_etoeflistz_0100_20121[/img][br]Listenagainto
Economics[img]2012q1/ct_etoefm_etoeflistz_0100_20121[/img][br]Accordingtothe
Economics[img]2012q1/ct_etoefm_etoeflistz_0100_20121[/img][br]Listenagainto
Economics[img]2012q1/ct_etoefm_etoeflistz_0100_20121[/img][br]Accordingtothe
Economics[img]2012q1/ct_etoefm_etoeflistz_0100_20121[/img][br]Whydothestude
随机试题
Wal-MartA)Wal-Martismorethanjusttheworld’
用木瓜蛋白酶将IgG分子水解为()A.2个Fab片段和Fc段 B. C.
尾矿库安全度主要根据尾矿库防洪能力和尾矿坝坝体稳定性确定,分为()。A.危库、正
A.质量为2m的滑块受到重力、绳的张力、沿斜面的下滑力和斜面的支持力的作用 B
香溪河上的宝坪村,是王昭君的故乡,这个看着并不起眼的________却孕育了一代
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性: A.如
各种运输方式内外部的各个方面的构成和联系,就是( )。 A.运输系统
下列哪一行为不违反《土地管理法》的规定?A.某军队转让以政府划拨方式获得的土地使
计算某年的婴儿死亡率,其分母是A.年初0岁组人口数 B.年末0岁组人口数 C
低钾血症时,最早出现的临床表现是A.心电图改变 B.肌乏力 C.口苦、恶心
最新回复
(
0
)