Download Chapter 4 Science Study Guide

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.