Download Weathering, Mass Wasting and Karst

Weathering, Mass Wasting and Karst
• 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
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
• 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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• 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
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
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Structure of bedrock
Size of openings
Climatic conditions
Vegetative cover
Variety of digging animals
Mechanical Weathering
• The physical disintegration of rock material
without any change to its chemical composition
• Big rocks fractured into smaller rocks
• Frost Wedging
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Most important mechanical weathering agent
Water freezes from the top down
Expanding wedge exerts pressure on rock
Repeated cycle of freeze and thaw
Exfoliation
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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
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
• 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
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
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
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
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
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
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
Karst Topography
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15% of the Earth’s surface
Limestone
Pitted and bumpy surface
poor drainage
Vast underground caverns
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Formation of Karst
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80% calcium carbonate
Pattern of joints
zone of air between ground and water table
Vegetation to supply organic acids
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Features of Karst Landscapes
• Sinkholes
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Solution sinkhole
collapse sinkhole
Watertable lowering
Construction
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• Caves and Caverns
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Limestone easily dissolves
Forms just below water table
Flowing water
Unique plant and animal
species
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