over long periods of timewithout obvious motion 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 occurs at a slower rate than erosion. Erosion involves obvious motion when breaking down rock
Cause by water freezing Common in high elevations and mid latitudes (Michigan)
Removing overburden relieves pressure Outer layer peels off like onion skin Occurs mainly in intrusive igneous rocks ◦ batholiths
3. Mudcracks When water evaporates- mud shrinks Wet/dry climates
Lichen secrete acid dissolve rock Tree roots- growth breaks rocks Humid climates Usually sed. rock
Change in composition (decomposition)
Water + carbon dioxide = carbonic acid H 2 O + CO 2 H 2 CO 3 Acid reacts (dissolves) with calcite (limestone, marble) May create caves and sinkholes
Marble statue
where iron minerals produce iron oxide ("rust"). Often in ss from iron in groundwater OR mafic rocks Fe + O 2 (atm) Iron Oxide Fe 2 O 3
Hydrolysis Reaction with water feldspar + carbonic acid +water clay + salt common in granite Result- holes in granite
Water enters cracks in rock and weathers the edges and creates a rounded shape Any rock type Result- rounded spheres t
Time- more time; more weathering Rock Type/Resistance ◦ Sedimentary least resistant- esp. calcite Climate ◦ Wet- chemical dominates ◦ Freeze/thaw- physical dominates Surface area
Smaller pieces (more surface area)= more weathering
Cleopatra’s Needle (Egypt) 3,000 years old
Cleopatra’s Needle (New York) 100 years old
Not all rocks weather equally
Different rock types weather differently OR Different rates of weathering due to cracks
limestone shale
Tall spires of rock Often “balancing” Softer rock (shale) erodes faster than cap rock
Thoughts?