关闭图标
log图标

toefl.viplgw.cn

  • 使用手机注册
  • 使用邮箱注册
  • 手机号不能为空!

    验证码不能为空!

    用户名不能为空!

    密码不能为空!

  • 邮箱不能为空!

    验证码不能为空!

    用户名不能为空!

    密码不能为空!

已有账号? 登录到雷哥托福
关闭图标
log图标
  • 使用手机找回密码
  • 使用邮箱找回密码
  • 手机号不能为空!

    验证码不能为空!

    密码不能为空!

  • 邮箱不能为空!

    验证码不能为空!

    密码不能为空!

又想起来了
加入生词本

listen

英['lɪs(ə)n] 美['lɪsn]
vi. 听,倾听;听从,听信
n. 听,倾听

已添加
×

我要举报草莓小菇凉评论

用户头像
草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

请选择举报类型:

举报电话:400 1816 180    举报QQ:2095453331
×
logo图标
分享到雷哥托福

分享成功图标分享成功

邀请名师点评成功,管理员正在安排老师进行点评。

继续做题 返回首页
支付雷豆失败图标 雷豆余额不足 购买雷豆 返回
报告题目错误
请选择错误类型:
请描述一下这个错误:

取消

文章结构

TPO 49-L1 .Alaska geologists 点击收藏

标准

  • 高音
  • 静音
  • 句子
    精听
  • 全文
    精听
  • 听写
    模式
  • 点击查看本句

    听写本句 再播一遍 下一句
  • 点击查看全文

    再播一遍本文

    Listen to part of a lecture in a geology class.

    Alaska is fascinating to geologists because of its incredible landscapes.

    Permafrost has a lot to do with this.

    That is the areas where the ground,the soil,is always frozen,except for the very top layer,

    what we call the active layer of permafrost,which melts in the summer and refreezes again in the winter.

    The northern part of Alaska is covered in lakes,thousands of them.

    And most of these are what we call thaw lakes,T-H-A-W,thaw lakes.

    I'm going to show you a few sketches of them in a minute,

    so you'll have a good idea of what I'm talking about.

    So how these thaw lakes are formed has to do with...

    OK.It start with ice wedges.

    The top part of the ice wedge melts.

    Should I back up?

    Ice wedges form when water runs into cracks in the ground,the permafrost,then freezes.

    You ever see mud after it dries?

    Dried mud has cracks because when it dries it contracts,it shrinks.

    Well,in winter permafrost behaves similarly.

    It shrinks in winter because it freezes even more thoroughly then.

    And as it shrinks,it froms deep,deep cracks.

    Then in the summer,when the active layer,the top layer of the permafrost,melts,

    the melt water runs into those cracks in the permafrost,

    then freezes again,because that ground,the ground beneath the active layer is still below freezing.

    So you have wedges of ice in the permafrost.

    Now,the ice wedges widen the original cracks in the permafrost because water expands when it freezes.

    All right,OK.

    Then in the autumn,the active layer on top freezes again.

    Then in winter the permafrost starts contracting again and the cracks open up even wider.

    So the next summer when the active layer melts again and flows into the widened cracks and freezes,

    it makes the cracks even wider.

    So it's sort of a cycle through which the cracks and the wedges grow wider and wider.

    So when the ice wedge reaches a certain size,

    its top part in the active layer turns into a little pond when it melts in the summer.

    And that's the beginning of your thaw lake.

    There are thousands of them in Northern Alaska.

    One of the most fascinating things about these lakes and this is important,

    is that they mostly have the same shape like an elongated oval or egg shape,

    and what's more,

    all the ovals are oriented in the same way.

    Here is an idea of what they look like,

    what the landscape looks like from an aerial view with the lakes side by side.

    There's been considerable research done to try to figure out what causes them to be shaped and oriented this way.

    We know that the shape and orientation are caused by the way the lakes grow once they are formed.

    But the question is what makes them grow this way?

    One theory sees winds as the cause.

    This region of Alaska has strong winds that blow perpendicular to the lakes.

    What happens is wind blows straight into the longer side of the lakes.

    Now,wouldn't that erode the lake bank in that direction?

    Same direction as the wind?

    Well,no.

    Actually,what happens is that the waves caused by the winds build a sort of protective layer of sediment.

    It's called a protective shelf along the bank of the lake directly in front of them.

    So that bank is shielded from erosion and the waves are diverted to the sides,to the left and to the right.

    And that's why the left and the right banks start eroding.

    Get it?The bank straight ahead is protected.

    But the lake currents,the waves erode the banks to the sides.

    That's the current model,the wind erosion model,which is generally accepted.

    But there is a new theory that says that thaw slumping,not wind,is what shapes the thaw lakes.

    Thaw slumping...

    Ok.Sometimes in the summer the temperature rises pretty quickly.

    So the active layer of permafrost thaws faster than the water can drain from the soil.

    So the sides of the thaw lakes get like mushy and slump or slide into the lake.

    Then the lake water spreads out more and the lake gets bigger.OK?

    Also in that part of Alaska the terrain is gently sloped,so the lakes are all on an incline.

    Here,now,this is an exaggeration of the angle.The hill is not this steep.

    But see how with the lake's banks,the side that is farther downhill,it's smaller,lower.

    This short bank thaws faster than the tall one does,so it falls into the lake,it slumps much more and much faster than the other bank.

    When short banks of many lakes slump,

    they move farther downhill and the lakes grow all in the same downhill direction.

    • special
    ☞查看答案 再播一遍

联系雷哥托福

全国免费咨询热线:400 1816 180

  • 上海(总部)
  • 北京
  • 成都
  • 杭州
  • 武汉
  • 南京
  • 广州
  • 西安
  • 重庆
  • 深圳
  • 上海(总部)服务中心

    电话:400 1816 180

    地址:上海市徐汇区文定路218号德必徐家汇WE艺术湾B座205

    公交路线:76路、93路、138路宜山路蒲汇塘路站;205路、732路、754路南丹路宜山路站;205路、754路、830路南丹路文定路站等

    地铁路线:地铁3号线、4号线宜山路站出站470m;地铁1号线、4号线上海体育馆站出站600m。

  • 北京服务中心

    电话:400 1816 180

    地址:北京市朝阳区雅宝路7号 E园EPARK大厦508

    公交路线:乘坐公交44路外环;58路;139路;特12路外环;特2路;夜20路外环到雅宝路公交站 下车,走140米即可达到。

    地铁路线:乘坐地铁1号线、2号线到建国门站(A出口)步行1000米即可到达;乘坐地铁2号线、6号线到朝阳门站(A出口)步行1200米即可到达雅宝路7号 E园EPARK大厦。

  • 成都服务中心

    电话:400 1816 180

    地址:成都市锦江区总府路31号Z31六楼(皇冠假日酒店旁)

    公交路线:乘坐58路、98路、锦城观光3号线、熊猫快线5号线在春熙路步行街北站下 步行约281米。

    地铁路线:乘坐地铁2号线或者3号线到春熙路C口下,步行约982米

  • 杭州服务中心

    电话:400 1816 180

    地址:杭州市江干区江锦路159号 平安金融中心B座8楼

    公交路线:901路、105路环线、106路环线、9M路:富春路民心路口站 176路:市民中心北大门站,市民中心西大门站

    地铁路线:号线钱江路站;4号线钱江路,江锦路

  • 武汉服务中心

    电话:400 1816 180

    地址:武汉市珞瑜路光谷世界城广场写字楼1栋1单元14层11421室

    公交路线:乘坐18路,25路,340路,510路,518路,521路等公交车到珞瑜路湖北省中医院站下车

    地铁路线:乘坐地铁2号线至珞雄路A口出,往湖北省中医院光谷院区方向步行50米至世界城广场写字楼

  • 南京服务中心

    电话:400 1816 180

    地址: 南京市秦淮区中山东路532号金蝶科技园 H1幢308号(林客社 内)

    公交路线:5路 34路 34路区间 36路 55路 59路 y5路夜间 17路 65路 115路 118路 y17路夜间

    地铁路线:地铁2号线明故宫站1号口出,向东200米

  • 广州服务中心

    电话:400 1816 180

    地址:广州市天河区体育西路103号维多利广场B座26楼K15

    公交路线:11,18,20,230,278,293,45,583,669,886冼村路中站下。 194,40,777,778,90,观光2路花城广场路站下。

    地铁路线:乘坐地铁APM线至花城大道站下B口出,步行约500米即可到达保利威座大厦北塔。

  • 西安服务中心

    电话:400 1816 180

    地址:西安市莲湖区北大街西华门十字西南角78号嘉会广场C座4层B021号

    公交路线:4路、12路、26路、36路、37路、229路、游7钟楼北站;15路、16路、32路、102路、182路、236路、286路西华门站。

    地铁路线:地铁二号线钟楼站150米;地铁一号线/二号线北大街站700米。

  • 重庆服务中心

    电话:400 1816 180

    地址:重庆市渝中区邹容路68号大都会广场16楼1603-1604室

    公交路线:401、135、114、111、401、151、862、181、262、105、866、153、466

    地铁路线:2号线临江门站500米、1号线小什字站500米、6号线小什字站500米。

  • 深圳服务中心

    电话:400 1816 180

    地址:深圳市罗湖区书城路都市名园B栋5楼B区(只接受预约拜访)

    公交路线:101路 10路 12路 203路 214路 215路 223路 29路 3路 85路 M112路 M191路 M192路 N3路 P100路(定制公交请预约) 高快巴士200号线 高快巴士20路 高快巴士863号线到地王大厦下,步行431米即可到达。

    地铁路线:乘坐1号线/罗宝线/2号线/蛇口线到大剧院(E口)出,步行498米即可到达都市名园B栋

预约托福考试规划师