Transcript Mechanical Weathering

Weathering, Soil, and
Mass Movement
What is
Weathering?

Is the breaking
down and changing
of rocks near
Earth’s surface
◦ Two Types:
Mechanical
(physical) and
Chemical
What is Mechanical
Weathering?
Mechanical Weathering:
Physical forces break
rock into smaller and
smaller pieces without
changing the rock’s
mineral composition.
Three Types of
Mechanical
Weathering
 Frost
Wedging
 Unloading
 Biological
Activity
Frost Wedging
Expansion of freezing water
in cracks and crevices
 Eventually breaking rocks
into pieces
• Sections of rock that are
wedged loose are called
talus

Unloading
• The uplift and erosion
of rocks overlying
igneous rocks because
pressure on igneous
rocks is reduce
• Exfoliation—slabs of
outer rock separate and
break loose
Biological Activity
• The activity of organisms,
including plants, burrowing
animals, and humans
• Plant roots wedge into rocks
breaking them apart
What is
Chemical
Weathering?
Chemical weathering:
the transformation of
rock into one or more
new compounds.
Agents and Evidence
of Chemical
Weathering
Water: most important agent
of chemical and mechanical
weathering. It picks up CO2
and SO2 in the air which forms
acid rain.
 Granite: Weathering of

potassium feldspar produces clay
minerals, soluble salt (potassium
bicarbonate), and silica in
solution. Quartz remains
unaltered.
Silicate Materials
and Spheroidal
Weathering

Weathering of Silicate
Minerals: Produces
insoluble iron oxides and clay
minerals
Spheroidal Weathering:
Causes the corners and
edges of rock to be more
rounded
Rate of
Weathering
How fast the rocks
erode
 Two factors

• Rock characteristics
• Mineral composition
and solubility
• Climate
• Temperature and
moisture
• Favors high
temperature and
abundant moisture
Soil
Soil: part of the
regolith that supports
the growth of plants.
Regolith: layer of rock
and mineral fragments
that covers most of
Earth’s land surface.
How is Soil
Formed?
Soil is formed by
rock being
eroded away.
Parent
material

Residual soil
◦ parent material is the
bedrock
 Transported soil
◦ parent material has
been carried from
elsewhere and
deposited
Characteristics of
Soil
Soil Composition

Soil has four major
components
A. Mineral matter
(broken-down rock)
B. Humus (decayed
remains of
organisms)
C. Water
D. Air
Characteristics of
Soil
Soil Texture
Texture refers to the
proportions of different
particle sizes.
A. Sand (large size)
B. Silt – feels like flour
C. Clay (small size)
D. Loam (a mixture of
all three sizes) is best
suited for plant life.
Characteristics of Soil
Characteristics
of Soil

Soil Structure
Soil particles clump
together to give a
soil its structure.
Time, Climate,
Organisms and
Slope
Time:
Important in all geologic processes.
The longer a soil has been forming, the
thicker it becomes.
Climate
Greatest effect on soil formation
Organisms
Furnish organic matter to soil
Slope
Steep slopes often have poorly
developed soils.
Soil Profile






O Horizon: Humus
A Horizon: Topsoil
E Horizon: Eluviation
layer
B Horizon: Subsoil
C Horizon: Regolith
R Horizon: Bedrock
Soil Types
Soil Types
Location
Contents
Pedalfer
under forest
vegetation
iron oxides and
aluminum-rich clays
in the B horizon
Pedocal
drier grasslands
Calcium
carbonate
Laterite
Hot, wet, tropical
climates
Intense chemical
weathering to the
top layers of soil
How does
water erode
the soil?
Rain uses gravity as a
force to move soil.
 Flash flooding and
runoff of water causes
erosion
 Strong winds move
particles

Processes of
Water Erosion
Sheet erosion 2. Rills (tiny streams)
3. Gullies (trenches)
4. Transports sediments
for deposits.
1.
How can humans
control erosion?
Planting rows of trees called
windbreaks
Terracing hillsides
Plowing along the contours of
hills
Rotating crops
What is Mass
Movement?

The transfer of
rock and soil
down-slope
due to gravity
Triggers of Mass Movement
Water
Heavy rains and rapid
melting of snow
Oversteepened Slopes
The steeper the slope the
greater the chance for
movement
Removal of vegetation
Roots keep the soil intact.
Removing plants causes
erosion
Earthquakes
Aftershocks dislodges rocks
causing movements
Classification of
Mass Movements

Rockfalls occurs
when rocks or rocks
fragments fall freely
through the air.
Classification of
Mass Movements
Avalanches
--extremely rapid
movement of earth
material or snow
Classification of
Mass Movements
Slides

In a slide, a block of
material moves
suddenly along a flat,
inclined surface.
Slides that include
segments of bedrock
are called rockslides.
Classification of
Mass Movements
Slumps
A slump is the
downward movement
of a block of material
along a curved
surface.
Classification of
Mass Movements
Flows
Flows are mass
movements of material
containing a large
amount of water.
Mudflows move quickly
and carry a mixture of
soil, rock, and water
that has a consistency
of
wet concrete.
Earthflows move
relatively slowly and
carry
clay-rich sediment.
Classification of
Mass
Movements
Creep is the slow,
downhill movement of
soil and regolith.
 slowest type of
mass movement