The Earth’s Changing Surface
What is Weathering?
• Weathering is the chemical and physical
processes that break down rock at Earth’s
surface.
• There are two types of weathering:
Chemical & Physical
Mechanical (Physical) Weathering
• The type of weathering in which rock is
PHYSICALLY broken down into smaller pieces.
Ice Wedging
• Repeated freezing and thawing of water in
cracks of a rock.
• Water seeps into cracks in rock and then
freezes.
• Rock is pushed apart by frozen water.
Plant Growth
• Roots act as wedging, causes cracks in
the rock.
• Roots exert constant pressure on rock.
• Eventually breaking
them apart.
Chemical Weathering
• The process that breaks down rock through
chemical changes.
Carbon Dioxide
• Carbon Dioxide from the air dissolves in
rainwater.
– Result: water that contains carbonic acid.
• A weak acid that reacts with minerals to break down
the rock.
• Limestone caves
Water
• Hydrolysis: the change in composition of
minerals when they react chemically with
water.
• Leaching: process of transferring
dissolved minerals to lower layers of rock
Acid Rain
• Rain contains carbonic acid.
• Fossil fuels release sulfur dioxide and
nitrogen oxides that react with water to form
sulfuric acid and nitric acid.
• falls to Earth as
acid rain
What is Erosion?
• Erosion –the process
by which natural forces
move weathered rock
and soil from one place
to another.
– It wears away parts of
the Earth’s surface.
– Gravity, running water,
wind, waves, ice,
underground water
Erosion (cont.)
• Sediment – is the material moved by erosion.
– Sediment may consist of:
• pieces of rock
• soil
• remains of plants and animals
• Both weathering and erosion produce
sediment.
What is Deposition?
• Deposition – drops
weathered material
(sediment) in new
places.
• The process by which
material is laid down.
– It changes the shape of
the land by building new
land forms.
• Weathering, erosion, and deposition act
together in a cycle that wears down and
builds up the Earth’s surface.
– Erosion and deposition are at work everywhere
on Earth
– The cycle of erosion and deposition is neverending.
Mass Movement
• Gravity is the force that moves rock and
other materials down hill.
– Gravity causes mass movement
• The different types of mass movement
include landslides,
mudflows, slump, and creep.
Mass movement can be
fast or slow.
Landslides
• This is the most
destructive type of
mass movement.
– Landslides occur when
rock and soil slide
quickly down a steep
slope.
• Some landslides contain
huge amounts of rock
and soil, some only
contain small amounts of
rock and soil.
Mudflows
• A mudflow is the rapid
downhill movement of a
mixture of water, rock, and
soil.
• Mudflows often occur after
heavy rains in a normally
dry area.
• Under certain conditions,
clay soils suddenly turn to
liquid and begins to flow.
– An earthquake can trigger
both mudflows and
landslides.
Slump
• A mass of rock and soil
suddenly slips down a
slope.
– The material in a slump
moves down in one
large mass.
Creep
• Creep is the very slow
movement of rock and
soil.
– Creep is so slow you
can barely notice it.
• Bent trees
• Cracked roads
• Leaning poles/fences