Chapter 1
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15
they created mountains. In the northeast,
the beautiful
Pocono Mountains
were
formed by glaciers. They rise over 2,000 feet
above sea level. North of Pittsburgh, the
land of Moraine State Park was created by
glaciers. A
moraine
is anarrow ridgeof soil,
rocks, and boulders. Today, there are no
glaciers located in Pennsylvania.
Erosion
I
n Pennsylvania,
erosion
is one of the
most easily seen natural forces. Erosion
is the wearing away of soil and land.
Water is themain agent of erosion. Streams
that start as far north as southernNewYork
State empty into larger streams and creeks.
These waterforms pick up soil and small
bits of rock. The soil and rock grind more
soil and rocks from our waterforms. The
forces of running water and the constant
grinding of soil and rock have carved out
many glens, rivers, and deep valleys in
Pennsylvania.
Water also causes another kind of land
erosion. This type of erosion is called
weathering. In
weathering
, water freezes
inside the cracks of rocks. The pressure
caused by the freezing breaks the rock into
smaller pieces. Water and winds carry this
material away to be deposited elsewhere.
Through millions of years of erosion,
rivers and streams have carved a rugged
landscape, especially in the Allegheny
Plateau. The natural forces of building up
and wearing down the land have created a
landscape of great variety and beauty in
Pennsylvania. Some of these natural forces
are occurring today.
ReviewQuestions
1. Use the definitions below to identify thewords they are describing:
a. process that breaks rock and soil into smaller pieces
b. process bywhich rocks and soil under the earth’s crust lift land
c. process bywhich a break in the earth’s crust causes land to rise or sink
d. a hugemass of thick ice
2. How did the folding process formmountains and plateaus?
3. Howwere land features changed by faulting?
4. How did glaciers build up land?
5. How did glaciers wear away the land?
6.Mt. Davis was not formed by a glacier. Howwas it formed?
7. How did glaciers change our waterforms?
8. How does erosion change our land?
