Weathering, Mass Wasting and Karst

Transcription

1 Weathering, Mass Wasting and Karst

2 Capable of wearing down anything that the internal processes can build. Gravity, water, wind and ice Denudation - the overall effect of disintegration, wearing away and removal of rock material Weathering Mass wasting Erosion

3 Weathering The first step in shaping the Earth s surface Mechanical disintegration or chemical decomposition Rock fragments into smaller and smaller pieces Occurs where atmosphere and lithosphere meet Whenever bedrock is exposed, it weathers Cracks and crevices allow weathering to penetrate bedrock Once started spreads

4 Joints are the most common Develops as a result of stress Most important in facilitating weathering Microscopic openings are tiny and numerous Responsible for extensive weathering

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6 Faults are breaks in bedrock with displacement Major landscape feature Easy penetration of weathering agents Lava Vesicles holes in cooling lava that allow gas to escape, later allows weathering to occur Solution Cavities holes formed as soluble minerals are dissolved

7 Weathering Agents Most atmospheric Easy to penetrate into cracks and crevices Oxygen, carbon dioxide and water vapor Temperature Weathering influenced by a variety of factors Structure of bedrock Size of openings Climatic conditions Vegetative cover Variety of digging animals

8 Mechanical Weathering The physical disintegration of rock material without any change to its chemical composition Big rocks fractured into smaller rocks Frost Wedging Most important mechanical weathering agent Water freezes from the top down Expanding wedge exerts pressure on rock Repeated cycle of freeze and thaw

9 Exfoliation Curved layers of peeled off bedrock Curved joints break away in succession Granite and other intrusive rocks Half Dome, Yosemite Valley, CA Not fully understood Rock cracks after overlying weight is removed Removal of weight allows expansion in rock

10 Chemical Weathering Decomposition of rock by the chemical alteration of its minerals Some rocks are extremely resistant Many others not resistant The greater the surface area exposed, the greater amount of weathering Requires moisture Higher temperature is better

11 Oxidation Oxygen atoms combine with metallic elements Can form new materials (Iron + Oxygen = Iron Oxide) Rusting Red stains on rocks Oxides are softer and easier to remove than original material

12 Biological Weathering Plants and animals contribute to weathering Tree roots into cracks and crevices Lichen Live on bare rock and draw nutrients from rock and weakens rock Burrowing Animals

13 Mass Wasting The process whereby weathered material is moved a relatively short distance down slope under the direct influence of gravity. Occurs even on gentle slopes Can fall abruptly or creep gradually Can be gigantic boulders or tiny particle of dust

14 Fall The falling off pieces of rock downslope Loosened by weathering Characteristic in mountainous areas Pieces of unsorted rock is known as talus Forms a talus cone at base of slope Some sorting by size Large talus cones can move down slope under own weight

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16 Slide An instantaneous collapse of a slope Rainwater adds weight to overloaded slope Earthquakes Detached along joints Topographic changes Extensive scar exposing bedrock and debris In the valley bottom, massive pile of irregular debris Up-valley of debris a lake may form

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18 Flow A sector of a slope becomes unstable and flows gently downhill Normally caused by excess water Relatively small and shallow Earthflow Most common During or after heavy rainfall Low vegetation

19 Creep Slowest and least noticeable Very gradual downhill movement of soil and regolith Happens everywhere there is a slope Water helps accelerate creep Any activity that disturbs soil can contribute Usually recognized only through displacement of human built structures

20 Karst Topography 20

21 15% of the Earth s surface Limestone Pitted and bumpy surface poor drainage Vast underground caverns 21

22 Formation of Karst 80% calcium carbonate Pattern of joints zone of air between ground and water table Vegetation to supply organic acids 22

23 Features of Karst Landscapes Sinkholes Solution sinkhole collapse sinkhole Watertable lowering Construction 23

24 Caves and Caverns Limestone easily dissolves Forms just below water table Flowing water Unique plant and animal species 24

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