Mechanical weathering can be caused by select all that apply. a. gravity b. acid rain c. freezing and thawing in the absence of water d. freezing and thawing in the presence of water user: which of the following can be an organic cause of chemical weathering? a. loess b. lichen c. freezing d. expansion

1- Option (A), (B) and (D)

2- Option (B)

Explanation:

Freeze and thaw is one of the mechanical weathering process that usually takes place in a colder type of environment. When the rocks in this region are comprised of fractures, then the water seeps into these fractures and at night due to the lowering of temperature, the water in these fractures gets freeze. Due to this freezing, the water expands and exerts a force on the side of these fractures that breaks the rock apart. This type of weathering process is known as the freeze and thaw method. In addition to this, gravity and acid rain also drives the mechanical weathering process. As the water flows from a higher region to a lower region, it erodes some of the materials with it that ultimately causes weathering and erosion. Acid rain is comprised of acids and when they precipitate, the minerals and the acid water reacts. As a result of which the rock weathers.  

The type of weathering in which the roots of plants or trees such as lichens, grow within the spaces (fractures) of the big boulders in the soils, then these trees or plants over a due course of time, breaks the boulders apart.

Hence, the correct answers are given above.

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