mechanical weathering

ice wedging

There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point (Figure 1.1). Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons. Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Ice wedging is common in Earths polar regions and mid latitudes, and also at higher elevations, such as in the mountains.

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mechanical weathering

Mechanical weathering (also called physical weathering) breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, but smaller. That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock.

organisms

Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering (Figure 1.3). This could happen slowly as a plants roots grow into a crack or fracture in rock and gradually grow larger, wedging open the crack. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves.

abrasion

Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a mountainside or cliff. Moving water causes abrasion as particles in the water collide and bump against one another. Strong winds carrying pieces of sand can sandblast surfaces. Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below. Abrasion makes rocks with sharp or jagged edges smooth and round. If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion (Figure 1.2).

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humans

Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting into rock to build homes, roads, and subways, or to quarry stone. (a) Humans are tremendous agents of mechanical weathering. (b) Salt weathering of building stone on the island of Gozo, Malta.

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instructional diagrams

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questions

what can cause mechanical weathering?

a) animals

b) ice

c) gravity

-->  d) all of the above

water that enters a crack, expands the crack as it freezes, and splits it apart.

a) abrasion

b) wind erosion

c) water erosion

-->  d) ice wedging

the most common form of mechanical weathering in locations like the eastern and midwestern united states and the mountains of california is

a) water erosion

-->  b) ice wedging

c) abrasion

d) wind erosion

mechanical weathering breaks down existing rocks by

a) changing them chemically, but not physically.

-->  b) changing them physically, but not chemically.

c) changing them chemically and physically.

d) incorporating them into new rocks.

which of these can cause abrasion?

a) animals

b) plants

-->  c) gravity

d) all of the above

which of these are signs of abrasion?

-->  a) scratches from rocks in a moving glacier

b) rocks changing color

c) iron turning into rust

d) cracks made by ice

put the steps of ice wedging in order. i. water freezes ii. water seeps into cracks iii. frozen water expands the rock iv. water thaws and over time the rock breaks into pieces

a) iv, iii, ii, i

b) iv, ii, i, iii

-->  c) ii, i, iii, iv

d) ii, iii, i, iv

ice wedging is common at where temperatures commonly vary between above and below freezing.

-->  a) true

b) false

moving water can cause abrasion by

-->  a) making rocks tumble down a slope.

b) striking the rock.

c) sandblasting the rock.

d) none of these.

mechanical weathering includes

a) plant roots growing into a crack and widening it.

b) burrowing animals breaking rock as they dig.

c) humans digging up rock for construction.

-->  d) all of these.

diagram questions

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