Download Mechanical Weathering

Weathering
The “W” in W.E.D.L.
Weathering
Weathering - The process of breaking
down rocks into smaller pieces.
Two Types:
 Mechanical Weathering - Physically breaking rocks.
 Chemical Weathering - Chemically changing rocks.
Mechanical Weathering
Ice Wedging/Frost Action - The
repeated freezing and melting of water.
Water seeps into a small opening or
crack. When it freezes it expands and
the crack widens. The constant freezing
and melting breaks the rock apart.
Mechanical Weathering
Organic
Activity/Roots
Roots of plants can
hold soil.
Root Pry--As plant
roots grow they
expand the crack.
Mechanical Weathering
Thermal Expansion
The changes in temp.
from night to day
causes particles of rock
to break and flake off.
Exfoliation - When the
particles break off in
parallel sheets.
Mechanical Weathering
Abrasion -Wearing
away of rocks by
particles carried by
wind, water or other
forces.
 In deserts wind easily
moves sand particles
and creates unusual
shapes.
 River water carries
particles that wear
sharp rocks into smooth
round stones.
Mass Wasting - Landslide, Mudslide,
Mechanical
Weathering
Lahars
Gravity - Pulls loosened rock down a
cliff. As the rocks fall they collide and
break into smaller pieces. Occurs on
steep slopes and where roads have
been cut thru a mountain. Creates
Talus slopes.
Chemical Weathering
Changes occur in the chemical makeup
of the rocks.
Water can dissolve the minerals that hold
rocks together.
Minerals in a rock absorb the water like a
sponge and break apart.
Water mixed with acids cause minerals to
change the rock into a new rock.
Chemical Weathering
 Oxidation
Oxygen chemically
combines with
another substance.
Iron combines with
O2 in the air and
makes iron oxide
(rust). The rocks
turn red, this
indicates oxidation
is occurring.
Qxygen mixes with
Copper it makes
rocks green.
Chemical Weathering
Carbonation
Carbon dioxide in the air dissolves in rain, a weak
carbonic acid is formed.
This weak acid is able to dissolve some kinds of
rocks, like feldspar and limestone.
This makes Caves and Karst topography.
Acid Rain/Sulfuric Acid
Forms from the burning of coal.
Strong acid that will wear away and corrode rocks,
metal and other material quickly.
Acid Rain also kills forests & lakes/ponds.
Chemical Weathering
Plant Acids
Lichens and mosses
produce a weak acid
that may dissolve
rocks and minerals.
The rocks break into
smaller and smaller
pieces.
This process, is
important in soil
formation.
Climate & Rate of Weathering
 The rate of weathering
depends on: the type of
rock and the climate it is
in.
 The composition of the
Rock
 Type of minerals in the rock
 The climate
 Rocks in cool or warm dry
climates weathers slowly.
 Rocks in warm, humid
climates with moisture and
weak plant acids will
dissolve quickly
Amount of time rock
is exposed.
Amount of exposed
surface area
As rocks break down
more surface area is
exposed and it
breaks down faster.
Human impact on Weathering