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
MASS WASTING PROCESSES 1 The downslope movement of rock, mud, or other material under the influence of gravity is known as mas
MASS WASTING PROCESSES 1 The downslope movement of rock, mud, or other material under the influence of gravity is known as mas
admin
2012-01-14
54
问题
MASS WASTING PROCESSES
1 The downslope movement of rock, mud, or other material under the influence of gravity is known as mass wasting. While the angle of the slope is a major factor in the potential for mass wasting, the slope is not the sole determiner of mass wasting events. Water plays a significant role, especially where it is plentiful during the rainy season. Earthquakes may cause rockslides, mudflows, and other mass movements. Factors such as the presence or absence of vegetation and human activities can also influence the potential for mass wasting.
2 One way to classify mass wasting processes is on the basis of the material involved, such as rock, debris, earth, or mud. The manner in which the material moves is also important and is generally described as a fall, a slide, or a flow. A fall occurs when weathering loosens boulders from cliffs or rock faces, causing the boulders to break away and fall. A slide takes place whenever material remains fairly coherent and moves along a well-defined surface. A flow involves the movement of debris containing a large amount of water.
3 Many mass wasting processes are described as slides. Rockslides occur when a coherent mass of rock breaks loose and slides down a slope as a unit. If the material involved is mostly separate pieces, it is called a debris slide. Slides are among the fastest and most destructive mass movements. Usually rockslides occur in a geologic setting where the rock layers are inclined, or where there are joints and fractures in the rock that are parallel to the slope. When such a rock unit is undercut at the base of the slope, it loses support and the rock eventually collapses. Rain or snowmelt can
trigger
a rockslide by wetting the underlying surface to the point that friction can no longer hold the rock in place. The fastest type of slide is a rock avalanche, in which a mass of rock literally floats on air as it moves downslope. The high speed of a rock avalanche is the result of air becoming trapped and compressed beneath the falling mass of debris, allowing it to move down the slope as a
buoyant
sheet.
4 Mudflows are relatively rapid mass wasting events that involve soil and a large amount of water. Because of their fluid properties, mudflows follow canyons and stream channels. Mudflows often take place in semiarid mountainous regions and on the slopes of some volcanoes. Although rainstorms in semiarid regions are infrequent, they are typically heavy when they occur. When a rainstorm or rapidly melting snow creates a sudden flood, large quantities of soil and loose rock are washed into nearby stream channels because there is usually little or no vegetation to
anchor
the surface material. The result is a flowing mass of well-mixed mud, soil, rock, and water. The consistency of the mudflow may be similar to
that
of wet concrete, or it may be a soupy mixture not much thicker than muddy water. The water content influences the rate of flow across the surface. When a mudflow is dense, it moves more slowly, but it can easily carry or push large boulders, trees, and even houses along with it.
5 In dry mountainous areas such as southern California, mudflows are a serious hazard to development on and near canyon hillsides.
The removal of native vegetation by brush fires has increased the probability of these destructive events.
Past mudflows have contributed to the buildup of fan-shaped deposits at canyon mouths. Such fans are relatively easy to build on and often have scenic views, so many have become desirable sites for residential development. However, because mudflows occur infrequently, homeowners are often unaware of the potential danger of building on the site of a previous mudflow.
6 Highly fluid, fast-flowing mudflows incorporate fine-grained sediment and are common after volcanic eruptions that produce large volumes of volcanic ash. Mudflows containing volcanic debris are called lahars, a word originating in Indonesia, a region that experiences many volcanic eruptions. Lahars occur when highly unstable layers of ash and debris become saturated with water and flow down steep volcanic slopes along stream channels. In the northwestern United States, the eruption of Mount St. Helens in 1980 created several lahars that
raced
down the valley of the Toutle River, altering the landscape in a relatively short period.
Look at the four squares,A,B,C , and D , which indicate where the following sentence could be added to the passage. Where would the sentence best fit?
Thus, rockslides occur more frequently during the spring, when heavy rains and melting snow are most prevalent.
Many mass wasting processes are described as slides. Rockslides occur when a coherent mass of rock breaks loose and slides down a slope as a unit.A If the material involved is largely unconsolidated, it is called a debris slide. Slides are among the fastest and most destructive mass movements. Usually rockslides occur in a geologic setting where the rock layers are inclined, or where there are joints and fractures in the rock that are parallel to the slope.B When such a rock unit is undercut at the base of the slope, it loses support and the rock eventually collapses. Rain or snowmelt can trigger a rockslide by wetting the underlying surface to the point that friction can no longer hold the rock in place.C The fastest type of slide is a rock avalanche, in which a mass of rock literally floats on air as it moves downslope. The high speed of a rock avalanche is the result of air becoming trapped and compressed beneath the falling mass of debris, allowing it to move down the slope as a buoyant sheet. D
选项
A、
B、
C、
D、
答案
C
解析
In the added sentence, Thus is a transition that shows result. Thus links Rain or snowmelt can trigger a rockslide in the previous sentence with rockslides occur more frequently during the spring. when heavy rains and melting snow are most prevalent in the added sentence. (1.8)
转载请注明原文地址:https://kaotiyun.com/show/uWyO777K
0
托福(TOEFL)
相关试题推荐
Lookatthefollowingstatements(Questions37-40)andthelistofresearchersbelow.Matcheachstatementwiththecorrectrese
ClassifythefollowinginformationasreferringtoAadoptedthewritingsystemfromanothercountryBusedorganicmaterialst
ClassifythefollowinginformationasreferringtoAadoptedthewritingsystemfromanothercountryBusedorganicmaterialst
Youshouldspendabout20minutesonQuestions27-40whicharebasedonReadingPassage3below.Helium’sFutureUpintheAirA
ClassifythefollowingcharacteristicsasrelatingtoASocialScienceBMedicalScienceCBothSocialScienceandMedicalScien
Youshouldspendabout20minutesonQuestions1-13,whicharebasedonReadingPassage1below.AverybriefhistoryoftimeTh
TheEvolutionaryMystery:CrocodileSurvivesA.Eventhoughcrocodileshaveexistedfor200millionyears,they’reanything
【1】Whatistotheleftofthelostpropertyoffice?
Theprofessorsaysthatsuperhighways______.【26】
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
随机试题
女性,26岁。因甲状腺功能亢进症行甲状腺切除,术后第二天出现手足抽搐最可能的原因是
阻断双侧颈总动脉可使
2006年5月17日,马来西亚人陈某驾驶货轮在我国领海运输我国限制进口货物,被我国某海关查获。某海关经查认定,陈某运输的以上货物无合法证明,其以运往马来西亚海防为名,实际准备运往我国内地。某海关认定陈某的行为已构成走私,决定没收其所有物品。香港某有限公司不
色调由色彩的()三要素决定。
工业项目的可行性研究报告一般应包括()。
结构素描和__________是素描两大体系。
根据以下情境材料,回答问题。棚户区改造工程在某县全面推进。但日前在社会上谣传政府将对租房户进行补贴,广大租房群众为能及时得到补贴到政府门口聚集请愿。5月8日下午16时,在县政府门前聚集群众最多时达到1000余人,110指挥中心立即指令巡特警大队警力到现场
某人同时购买2年期、5年期和10年期三种国债,投资额的比为5:3:2。后又以与前次相同的投资总额全部购买5年期国债,则此人两次对5年期国债的投资额占两次总投资额的比例是( )。
Interestreferstotheamountwhatyourmoneyearnswhenitiskeptinasavingsinstrument.
Manychildrenfirstlearnthevalueofmoneybyreceivinganallowance.Thepurposeistoletchildrenlearn(1)______experienc
最新回复
(
0
)