Why can biological weathering be categorized as both physical and ...

[washai]

Why can biological weathering be categorized as both physical and chemical weathering?

Question 2

Describe the heaving process that results in soil creep.

[fwbard]

Answer to Question 1

Plant roots physically wedge into andexpand cracks in rocks causing them to break further. Mechanicalbreakage of rocks also occurs when trees in rocky terrainare knocked over and uprooted, such as by strong winds. Acids from decaying organic matter contributeto chemical weathering by solution. Lichens growing on rockscan physically dislodge particles and they also secrete acidicsubstances that mix with water from precipitation encouragingchemical weathering by solution.

Answer to Question 2

Freezing and thawing of soil water,and wetting and drying of soils or clay minerals, can lead to soilheaving. For example, when soil water freezes, it expands, pushingoverlying soil particles upward relative to the surface of the slope.When that ice thaws, the soil particles move back, but not to theiroriginal positions because the force of gravity pulls downward. Soil creep results fromrepeated cycles of expansion and contraction related to freezingand thawing, or wetting and drying, which cause lifting followedby the downslope movement of soil and rock particles.