Mechanical & Chemical Weathering

Mechanical weathering is when rock is physically broken into smaller pieces. The smaller pieces have the same composition as the larger pieces they came from. Mechanical weathering works slowly. Over time, it can eventually wear away whole mountains.

Freezing & Thawing Water freezes and expands that creates large cracks in the rock.

Animal Actions Burrowing in the ground will loosen and break apart rocks.

Plant Growth Tree roots enter cracks in rocks and force cracks farther apart

Abrasion Sand and rock particles can wear away exposed rock surfaces like sand paper

Release of Pressure When materials are removed from the surface of a rock, pressure is reduced. This can cause layers of rock to flake off.

Chemical Weathering

Chemical weathering can produce new materials as it breaks down rock. Chemical weathering is the process that breaks down rock through chemical changes. Chemical weathering can produce new materials as it breaks down rock. Granite is made of feldspar, quartz, mica and other materials. Chemical weathering eventually changes feldspar to clay.

Water weathers rock by dissolving it.

Oxygen Found in the air and combines with Earth’s materials. Combines with iron to create rust – oxidation Can happen to rock that contains iron.

Carbon Dioxide Found in the air and dissolves in rain water Creates carbonic acid. Weathers marble and limestone.

Living Organisms As plants grow, they produce a weak acid.

Acid Rain Air pollution chemically reacts with water vapor in the cloud. The acid mixes with rain drops.

Rate of Weathering Some variables can affect the rate at which rock is weathered. Type of Rock – some minerals that make up the rock weather faster than others. Climate – weathering occurs faster in wet climates. Chemical reactions occur faster in higher temperatures Human Activities – air pollution, factories, etc.

LEFT PAGE: Comparing Mechanical and Chemical Weathering Draw a Venn diagram comparing and contrasting mechanical and chemical weathering.