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  Occurs mainly in intrusive igneous rocks ◦ batholiths

3. Mudcracks  When water evaporates- mud shrinks  Wet/dry climates

Tree roots Growth breaks rock Lichen secrete acid dissolve rock  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

Cave Formation

 where iron minerals produce iron oxide ("rust"). Mafic rocks  Fe + O 2 (atm) Iron Oxide  Fe 2 O 3

 Hydrolysis  Reaction with water  feldspar + carbonic acid + water clay + soluble minerals  common in granite

 Water weathers the edges and creates a rounded shape  Aka onion skin weathering basalt

 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

Cleopatra’s Needle (New York) After 100 years

 Not all rocks weather equally

 Different rock types weather differently  OR  Different rates of weathering due to exposure