The Changing Earth
Chapter Fourteen: Weathering
and Erosion
• 14.1 Weathering
• 14.2 Erosion
• 14.3 Rivers Shape the Land
Investigation 14A
Water Systems
• How does running water shape rivers and
landscapes?
14.1 Weathering
• Mountains wear
down over time.
• Due to the Sun’s
energy, wind, and
water, mountains
begin to crumble as
soon as they are
formed.
14.1 Weathering
• The Smokey Mountains are much older than
the Rocky Mountains.
How do these two mountain ranges differ?
14.1 Weathering
• At one time, the Smokies were as tall as
the Rockies and also had sharp peaks.
How long did the weathering of the Smokies take?
14.1 Ways weathering occurs
• Mechanical
weathering occurs
when forces break
or chip rocks and
minerals into
smaller pieces
without changing
their composition.
14.1 Ways weathering occurs
• Rock is also
reduced to smaller
pieces by chemical
reactions between
water and rock
grains.
• This process is
called chemical
weathering.
14.1 Agents of mechanical
weathering
•
•
Changing conditions of wetness and dryness
cause rocks and minerals to break down.
Weathering occurs quickly when running water
knocks rocks against each other.
14.1 Agents of mechanical
weathering
• Frost wedging splits
apart rock slowly as
water freezes.
• When ice expands
and water contracts,
it causes more
cracks in rock.
14.1 Agents of mechanical
weathering
• Plants cause weathering
when their roots grow
into small cracks in a
rock.
• Animals cause
weathering when they
dig into soil or burrow
underground.
14.1 Agents of mechanical
weathering
• Exfoliation is a
weathering process
that results in rock
layers peeling away
as they expand or
contract.
14.1 Agents of mechanical
weathering
• Even wind is a
weathering agent.
• Wind-blown sand
chips away tiny bits
of rock from the
surface of exposed
rock.
14.1 Chemical weathering
• Moss and lichens
on rocks and will
eventually cause
them to break down
because of
chemicals they
release.
14.1 Chemical weathering
• Both physical
and chemical
weathering
can affect rock
at the same
time.
14.1 Factors that
affect weathering
• Weathering is slowest in dry,
cold climates.
• Running water speeds up mechanical
weathering and chemical weathering.
• The kind of minerals found in a rock also affects
how fast it weathers.
• The greater the surface area of a rock or mineral
compared to its volume, the faster it will weather.