Grass leaves and stems that die off above ground every year following the growing season break down slowly and mainly through oxidation in sunlight and physical weathering in the more brittle environments.
12.
Additionally, the group has studied of the deposition of mercury on the landscape in the U . S . and in Antarctica, and led investigations of chemical and physical weathering of rocks of high-standing oceanic islands like Taiwan and New Zealand.
13.
In such cases, the loosening and detachment of blocks appears to result from a combination of ( 1 ) chemical and physical weathering along joints, ( 2 ) hydraulic wedging driven by smaller rock fragments getting into existing cracks, ( 3 ) crack propagation from stresses caused by impacts of large clasts already in transport by the river, and possibly ( 4 ) crack propagation driven by flexing resulting from pressure variation in the overlying water during floods.
