Download Weathering and erosion

Weathering
Weathering
The process by which rock materials are broken down by
physical or chemical processes
2 types of weathering
◦ Mechanical weathering
◦ Chemical weathering
Mechanical Weathering
The breakdown of rocks into smaller pieces by physical means
Mechanical weathering can occur due to:
◦ Ice
◦ Abrasion
◦ Water
◦ Wind
◦ Gravity
◦ Plants
◦ Animals
Mechanical Weathering:
Ice
Frost Action: The freezing and
thawing of soil and rock
Ice wedging is a type of frost action
◦
Water seeps into cracks during warm
weather
◦
When temperatures drop, the water
freezes and expands
◦
The ice pushes against the sides of
the crack causing the crack to widen
Ice Wedging
Mechanical Weathering:
Abrasion
Abrasion: the grinding and wearing away of rock surfaces through
the mechanical action of other rock or sand particles
Mechanical Weathering:
3 Forms of Abrasion
◦ Water – Rocks in rivers bump and
scrape each other as they are
carried by the water, causing
them to become smooth and
rounded
◦ Wind – Wind blows sand against
rock causing wearing away the
rock’s surface
◦ Gravity – As rocks fall on one
another, they crack, scrape and
break into smaller pieces
Water Abrasion
Wind Abrasion
Gravity Abrasion
Mechanical Weathering:
Plants & Animals
Plants
◦ As a plant grows, the force of the
expanding root becomes so strong
that it can break a rock apart
Animals
◦ Almost any animal that burrows
causes mechanical weathering by
mixing and digging through soil and
rock particles
Plants
Animals
The Shape of Rocks
Weathering takes place on the
outer surface of rocks
The more surface area that is
exposed to weathering, the
faster the rock will be worn
down
Smaller rocks have more surface
area and therefore weather
more quickly
Chemical Weathering
The process by which rocks break down as a result of chemical
reactions
Chemical weathering can occur due to
◦ Water
◦ Acid
◦ Air
Chemical Weathering:
Water
Water chemically reacts with the minerals in a rock, causing those
minerals to become soft and breakdown
Chemical Weathering:
Acid
Acid Rain: rain, sleet, or
snow that contains
abnormally high
concentrations of acids
◦ Air pollution, from the
burning of coal and oil,
combines with water in
the atmosphere and falls
to earth as acid rain
◦ The acid in the rain
corrodes or chemically
destroys the rock
Acids in Groundwater
◦ Acidic groundwater
chemically reacts with
rocks in the ground, such
as limestone
◦ This chemical reaction
dissolves the limestone,
creating caverns
Acids in Living Things
◦ Some living things, such as
lichens, produce acids that
can slowly break down
rocks
Acid Rain
Acid Groundwater
Acid Organisms
Chemical Weathering:
Air
Oxidation: the chemical
reaction where iron combines
with oxygen in the air to form
rust
Rates of Weathering
Weathering takes a long time but some rocks with weather
faster than other rocks
3 Factors affect the rate of weathering:
◦ Makeup of the rock
◦ Climate
◦ Elevation
Differential Weathering
The process by which softer, less
weather resistant rocks wear away
and leave harder, more weather
resistant rocks behind
◦ Devils Tower was once deep inside an
active volcano
◦ After thousands of years of weathering,
the soft outer parts of the volcano have
worn away
◦ The harder, more resistant rock is all
that remains
Differential Weathering
Weathering & Climate
Climate is the average weather
condition in an area over a long
period of time
The rate of chemical weathering
is faster in warm, humid climates
◦ Oxidation happens faster when
temperatures are high and water is
present
Weathering & Elevation
Rocks at higher elevations, like
on a mountain, are exposed to
more wind, rain, and ice which
causes them to weather faster
Gravity pulls things, like water
and rocks, down faster
◦ Water carries rocks down the
mountain
◦ Rocks fall from the sides of the
mountain