Download Weath_Erosion_Soils_MS

HCDE-LPI Workshop on
Sedimentary Processes
Good Morning!!
Weathering…
Let’s break it down…
Weathering
• Chemical and physical alteration of rock and
minerals when exposed to air, moisture, and
organic matter
– Chemical weathering - minerals in a rock are
chemically altered or dissolved
– Physical weathering - solid rock fragmented by
mechanical breaking
Examples?
University of Georgia
What Controls the Rate of Weathering?
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Parent Material (minerals and structure)
Climate (rainfall and temperature)
Biology
Slope
Presence / Absence of Soil
Exposure Time
Chemical Weathering
• Chemical weathering - minerals in a rock are
chemically altered or dissolved
• Minerals weather at different rates because of
differences in chemical stability; the resistance of
a mineral to change
Which Minerals are More Stable?
Less?
Our Hero Bowen & His Reaction Series
Skinner and Porter, 1992
Physical Weathering
• Physical weathering - solid rock fragmented
by mechanical breaking
• Factors affecting:
– Slope
– Zones of weakness - joints
– Organisms - flora (and fauna)
– Freeze/thaw (frost wedging)
– Crystal growth
– Heat / Cold
Slope
• Things move downhill …. Why?
• Gravity aids in the breakdown and transport of material
• Slope starts it all!
Mass Movements (Mass Wasting)
• Mass movement is the down slope movement of
earth materials under the influence of gravity
www.physicalgeography.net
Rock Mass Movements
• Fall - fast; rocks break and fall
www.physicalgeography.net
www.geology.com
Rock Mass Movements
• Slide - (land slide)
moderate; rocks
slide as a unit
Source: USGS
Unconsolidated Mass Movements
• Creep - very slow flow downhill; top moves faster than
base
Source: North Dakota State University
Unconsolidated Mass Movement
• Slump - moderate; slide
of material as a unit
along a lower surface
(spoon-shaped)
Why Do We Care?
• Human Impacts of mass wasting …
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Year
1916
1920
1945
1949
1954
1962
1963
1970
1985
1987
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In a typical year in the United States, landslides cause over $1.5 billion in damages
and 25 to 50 deaths
Location
It/Aust
China
Japan
USSR
Austria
Peru
Italy
Peru
Columb
Ecuador
Type
Landslide
Earthquake triggered landslide
Flood triggered landslide
Earthquake triggered landslide
Landslide
Landslide
Landslide
Earthquake related debris avalanche
Mudflow related to volcanic eruption
Earthquake related landslide
Fatalities
10,000
200,000
1,200
12-20,000
200
4,000-5,000
2,000
70,000
23,000
1,000
http://www.tulane.edu/~sanelson/geol204/masswastproc.htm
Joints
http://www.geo.duke.edu/geo41/st045.gif
http://www.geo.duke.edu/geo41/wea017.gif
Chemical Weathering Along Joints
….. Where the Water Goes …..
Spheroidal Surfaces
http://www.geo.duke.edu/geo41/wea017.gif
Roots and
Critters
http://www.geo.duke.edu/geo41/wea003.gif
Crystal Growth
http://www.geo.duke.edu/geo41/wea001.gif
Frost Wedging
http://www.usd.edu/esci/figures/150651.JPG
In what environments will
chemical weathering be greatest?
Physical?