over long periods of timewithout obvious motion Def: the breaking apart of rock over long periods...
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Transcript of over long periods of timewithout obvious motion Def: the breaking apart of rock over long periods...
WeatheringCHAPTER 3
HONORS EARTH SCIENCE
Def: the breaking apart of rock over long periods of time and without obvious motion.
◦ Mechanical (Physical)- break into smaller pieces
◦ Chemical- chemical change in composition
Weathering
Weathering occurs at a slower rate than erosion.
Erosion involves obvious motion when breaking down rock
WEATHERING vs. EROSION
Cause by water freezing Common in high elevations and mid
latitudes (Michigan)
Physical Weathering1. FROST (ice)WEDGING
Bryce Canyon, utah
Potholes
Removing overburden relieves pressure Outer layer peels off like onion skin
Occurs mainly in intrusive igneous rocks◦ batholiths
Exfoliation (sheeting)
Half-dome; Yosemite
3. Mudcracks
When water evaporates- mud shrinks
Wet/dry climates
Septarian nodule;
BIOLOGIC ACTVITY
Lichen secrete aciddissolve rock
Tree roots- growth breaks rocks
Humid climates Usually sed. rock
Change in composition (decomposition)
Chemical weathering
Water + carbon dioxide = carbonic acid H2O + CO2 H2CO3
Acid reacts (dissolves) with calcite (limestone, marble)
May create caves and sinkholes
Dissolution
Sinkhole formation
Areas prone to sinkholes
Sinkhole in Corvette Museum, 2014
Guatemala, Sinkhole
MI sinkholes (near Alpena)
Marble statue
Dissolution
where iron minerals produce iron oxide ("rust").
Often in ss from iron in groundwater OR mafic rocks
Fe + O2 (atm) Iron Oxide
Fe2O3
CHEMICAL WEATHERING
2. Oxidation
Result- reddish stain
Pictured Rocks, MI
Hydrolysis Reaction with water
feldspar + carbonic acid +water clay + salt
common in granite
Result- holes in granite
CHEMICAL WEATHERING
Water enters cracks in rock and weathers the edges and creates a rounded shape
Any rock type Result- rounded spheres
Spheroidal weathering
t
Spherodial weathering
Time- more time; more weatheringRock Type/Resistance
◦ Sedimentary least resistant- esp. calciteClimate
◦ Wet- chemical dominates◦ Freeze/thaw- physical dominates
Surface area
Factors that affect Weathering
Smaller pieces (more surface area)= more weathering
Surface area
Climate
Cleopatra’s Needle
(Egypt)
3,000 years old
Cleopatra’s Needle
(New York)
100 years old
Not all rocks weather equally
Differential weathering
Different rock types weather differently
OR
Different rates of weathering due to cracks
Differential weathering
Arches National Park
Differential erosion
limestone shale
Hoodoos-
Tall spires of rock Often “balancing” Softer rock (shale) erodes faster than cap
rock
hoodoos
Thoughts?
Honeycomb weathering