Chapter 4 Science Study Guide

Test on Tuesday, February 24

Vocabulary

• weathering – the natural processes that break down rocks without transporting them

• physical weathering – the processes that change the size and shape of rocks without changing them chemically

• chemical weathering – the process by which rocks break down due to chemical changes in the minerals

• horizon – a layer of soil that is distinct from the layers above and below it

• erosion – the transportation of weathered rock from one place to another

• deposition – the dropping off of weathered rock at the end of erosion

• landform – a natural feature on Earth’s surface

• canyon – a deep, narrow valley with steep sides

• valley – an area of low land between hills or mountains

• delta – an area of land caused by deposition at the mouth, or end, of a river

• sand dune – hill-like deposit of sand left behind by wind erosion

• glacier – a large mass of moving ice

Examples of Physical Weathering

• Freezing and Thawing: Rainwater enters cracks in rocks. As it freezes, the water expands, causing the cracks to widen. Later the ice thaws.

• Plants: A plant’s roots can force their way into small cracks. As the roots grow, they

widen the cracks.

• Exfoliation: Some rocks, like granite, are buried. As the rock is exposed, the outer layers are peeled away like the layers of an onion.

• Abrasion: Winds carry bits of sand. The edges of the sand wear away rocks.

Examples of Chemical Weathering

• Oxygen: Oxygen in the air dissolves in water and reacts with iron to form rust.

• Acids: Decaying plants put acids in soil, rivers and lakes. Water soaking into the soil dissolves the acids. The acids react with a rock’s minerals, which

chemically changes the rock.

• Carbon dioxide: Carbon dioxide in the air combines with rainwater and forms carbonic acid (acid rain). This acid reacts with mineral in some rocks.

Compare and Contrast Physical and Chemical Weathering

• Both physical and chemical weathering cause rocks and minerals to break down into smaller parts.

• Physical weathering breaks down rocks without changing the minerals in the rocks.

• Chemical weathering changes the minerals in the rocks.

Erosion and Deposition

• Erosion takes weathered rock and soil from one place. Deposition leaves the weathered rock and soil in another place.

• Erosion takes away material from a place. Deposition leaves more material in a place.

Landforms

• Canyons are formed when a river takes material from the riverbed and washes it away. Over a long period of time, the riverbed goes deeper and deeper, forming a canyon.

• Valleys are formed when melting ice and snow in the mountains causes water to flow downhill into rivers. These rivers cut into the land along their sides, carrying away sediment. This forms a valley.

• When rivers reach flat land they slow, widen, and develop curves.

• Deltas are formed when rivers empty into the ocean. The river slows and drops a lot of sediment. This forms a delta.

• Glaciers are formed in cold areas where more snow falls than can melt. Glaciers move slowly over the land. They flow downhill, tearing up rocks from the land as they move. A glacier widens, deepens, and straightens a valley into a U shape.