WEATHERING GEOLOGY NOTES Chapter 5 WEATHERING 4 Breakdown of rock due to weather 4 no visible...
-
Upload
milton-short -
Category
Documents
-
view
226 -
download
0
Transcript of WEATHERING GEOLOGY NOTES Chapter 5 WEATHERING 4 Breakdown of rock due to weather 4 no visible...
WEATHERING
GEOLOGY NOTES
Chapter 5
WEATHERING
Breakdown of rock due to weather
no visible motion
MECHANICAL (PHYSICAL) WEATHERING
Disintegration
Breaks into small pieces
NO visible motion
MECHANICAL WEATHERING
Ice (frost wedging)–water expands
when freezes– angular pieces
MECHANICAL WEATHERING
Sheeting(exfoliation)–pressure is removed
from above–Fractures “peel” off
Half-dome
MECHANICAL WEATHERING
Other types– burrowing animals– Plant roots– Mud cracks
Mudcracks
When water evaporates- mud shrinks
CHEMICAL WEATHERING
Decomposition
chemical change takes place
CHEMICAL WEATHERING
Hydrolysis reacts with acid/water to form clays
feldspar + carbonic acid + water clay + soluble minerals
common in granite
CHEMICAL WEATHERING
DISSOLUTION
ANY CARBONATE + CARBONIC ACID CALCIUM CARBONATE (soluble)– common in limestone– creates caves and sinkholes
Parthenon, Greece
Sinkhole formation
Areas prone to sinkholes
Marble statue
Dissolution
CHEMICAL WEATHERING
OXIDATION–reacts with O2
–Groundwater with Fe is powerful agent
–minerals with high Fe content• hematite, limonite, olivine• intense in tropical climates
Oxidation of basalt
Pictured Rocks, MI
PLANES OF WEAKNESS
WHERE ROCKS WILL BREAK– Joints- vertical fractures–bedding planes- horizontal fractures–Granular disintegration- cement in clastic
rocks breaks down
joints
BEDDING PLANES
Granular disintegration
ROCK TYPES
Granite - exfoliation, hydrolysis (k-spar to clay)– quartz doesn’t weather
Basalt- chemical (oxidation) Sandstone- granular disintegration limestone- dissolution shale- breaks down into clay
Sandstone tombstone
Granite
Which rocks weather most rapidly?
sedimentary
Which rocks are most resistant to weathering? Igneous / metamorphic (exception?)
Bowen’s reaction series– Olivine most
Differential weathering
Different rock types weather differently
OR
Different rates of weathering due to exposure
Stairway to heaven, CO
Bryce Canyon, UT
Differential erosion
limestoneshale
Hoo-doos
CLIMATE AND WEATHERING
Chemical- warm and moist
Physical- freeze/thaw cycle
CLIMATE
TROPICAL– Strong chemical
DESERT– Slight mechanical
POLAR– Slight mechanical
MID LATITUDE (MI)– Strong chemical and mechanical