Assignment # _____
Name:_____________________________________________Date:________________Period:_____
Physical Weathering
Physical Weathering changes the size and shape of a rock by breaking it into smaller pieces.
This type of weathering does not change the rock's chemical composition. One way physical
weathering occurs is by frost action. Water seeps into cracks in the rock and freezes. As water freezes it
expands and makes the crack larger. Frost action occurs in climates that experience changes in
temperature above and below freezing. The alternate melting and freezing of water in the cracks causes
the rock to eventually crumble. A second way physical weathering occurs is from biological action.
Plant roots can grow in the cracks of a rock and expand, gradually pushing the rock apart. This is often
referred to as root action. Animals can also burrow beneath the ground. As they burrow they constantly
expose new rock surfaces to weathering. A third way physical weathering occurs is through the
collision with other rocks. This occurs as a stream rolls rocks which causes them to bump and rub
against one another. This causes the rocks to become smaller and rounder. Wind, moving ice, and
gravity can also move rocks so that they collide with one another. When these rocks crash into each
other, they get broken down by abrasion. Some rock minerals are more difficult to break than others.
These rocks are considered to be resistant to weathering.
Fill-in-the-Blanks:
1. ____________________weathering is the breakdown of rocks into smaller pieces.
2. This type of weathering does not change a .rock’s ____________________ composition.
3. ____________________ action occurs when water freezes and expands in a rock. .
4. ____________________ action occurs when plants further split the cracks in a rock.
5. As ____________________ burrow they constantly expose new rock to weathering.
6. Water, wind, ice, and gravity move rocks causing ____________________ as they collide. .
7. Rocks that do not weather easily are considered to be ____________________.
(Over for Chemical Weathering)
Chemical Weathering
Chemical Weathering is the breakdown of rock by changing its chemical composition to form a
new rock. When rocks are uplifted and exposed to the atmosphere, moisture reacts with the rock's
minerals and breaks them down. The rusting of a nail is a good example of chemical weathering. Iron
rusts when exposed to moisture and is chemically changed to iron oxide. Water and heat energy are
needed to bring about these chemical reactions. Chemical weathering takes place more rapidly in warm
and moist climates. Rain water that absorbs carbon dioxide from the atmosphere becomes acidic
causing acid rain. When this acidic precipitation falls onto unstable rocks, their chemical composition is
changed and chemical weathering has occurred. Some rocks are more resistant to chemical weathering
but limestone is not. Acidic water underground will break down limestone forming underground
tunnels that we know as caves. Marble statues and gravestones will also react with acid rain. We can
see that they are chemically broken down when details of statues and carvings in gravestones
disintegrate.
Fill-in-the-Blanks:
1. ____________________ weathering changes a rock’s chemical composition.
2. The ____________________ of a nail is a good example of chemical weathering.
3. Chemical weathering occurs most rapidly in places that are _______________ &_______________.
4. Precipitation combined with carbon dioxide causes ____________________ rain.
5. ____________________ are made underground when limestone is chemically “eaten” away.
6. Statues and gravestones made out of ____________________ will often deteriorate.