Download Weathering

Weathering of Rocks
Hoodoos
More Resistant layer
Breaking and Removing rock
1. Weathering - the disintegration and
decomposition of rock at or near the
surface.
2. Erosion – the transport of weathered
material by water, wind, ice and
gravity.
Weathering in the Rock Cycle
And
Sedimentary
Rocks
Metamorphic
Rocks
Weathering
and Erosion
Heat and Pressure
Magma
Sediment
Igneous
Rocks
*Types of Weathering
Mechanical – physical breakdown of
rocks with NO change in
composition.
Chemical – chemical alteration and
decomposition of rocks by
chemical reactions.
Mechanical Weathering makes
smaller pieces and exposes more
surface area to weathering
processes
*Types of Mechanical Weathering
1. Ice Wedging – water freezes in cracks and
expands them causing rocks to break
apart.
Ice Wedging
*Types of Mechanical Weathering
2. Organic Activity – roots break apart rocks.
Organic
Activity
Tree along 460 near Princeton that was saved
by building a huge cement wall with drainage
*Types of Mechanical Weathering
3. Exfoliation and Jointing because of
pressure release also break apart rocks.
Exfoliation
Exfoliation
Results of
Jointing
*Types of Mechanical Weathering
4. Abrasion –rounding or smoothing by water,
wind, or glaciers
Wind, water and glaciers also
erode/deposit sediments.
Glaciers smooth
and/or scratch
rocks.
Examples: Glacial
Striations
Glacial Polish
*Water transport in rivers
smooths and rounds rocks.
*Wind creates ventifacts
(smoothed surfaces and
erosion)
Wind and water work together
*Wind Deposition
creates Dunes
*Types of Chemical Weathering
Hydrolysis - any reaction in which
water participates. Also includes acid.
*Types of Chemical Weathering
1. Rust (oxidation) – caused by water and
oxygen
2. Carbonation (caves) – KARST topography
forms when carbonic acid (formed by
water and carbon dioxide) reacts with
limestone (Calcium Carbonate) and
converts it to soluble Calcium Bicarbonate.
*2a. Stalactites and stalagmites form
from carbonate deposits from
dripping water in caves.
*2b. Sinkholes can also cause
pollution problems if they connect
directly to the water table.
Typical Sinkhole
Not a Typical Sinkhole…
*Types of Chemical Weathering
3. Acids in mosses and roots can react with
minerals in rocks
and dissolve them.
4. Changing of feldspar into clay (kaolin) by
hydrolysis.
5. Dissolving by water.
*Factors influencing Weathering Rates
1.Rock Composition – sedimentary rocks
weather more rapidly than metamorphic or
igneous. Also, quartz is resistant to
weathering.
2.Rock Surface area – more surface
exposed, more rapidly weathered.
3.Topography – high elevation and steep
slopes weather more rapidly.
4.Climate – variable (freezes and thaws) and
hot/ humid cause rapid weathering.
Benefits of Weathering
• Produces regolith (rock fragments)
clay, sand, and gravel
• Produces minerals
• Creates soil
Soil is made of loose, weathered
rock, minerals, air and organic
material (humus).
Soil Profile(fill in the blanks)
0- Leaf Litter
A-Humus
B- Clay and
Leached
Minerals
C- Partially
Weathered
Bedrock
R
R-Bedrock or
Parent Rock
Soil Profile
In a crosssection of soil,
various horizons
are formed.
A Horizon: Topsoil
This layer is
usually loose
and crumbly with
a significant
amount of
organic matter
(HUMUS).
(O is leaf litter)
A Horizon: Topsoil
Most productive
layer of soil.
Conservation
efforts are
focused here!
B Horizon: Subsoils
Subsoils are
usually light,
dense, clay-rich
with some organic
matter. This is
where minerals
leached from the
A horizon
accumulate.
C Horizon: Transition
Partially
weathered parent
material with
little/no humus.
Bedrock
Below the C
horizon the
unweathered
bedrock will be
found.
Climate and Soil
Tropics – thick,
unfertile soils
called laterites.
Arctic or Desert
– thin, made
mostly of
regolith
Topography and Soil
Slopes – thin
and dry topsoil
Lowlands – thick,
wet soils with
humus
Erosion
Control
Creating a
soil
condition
that is
resistant to
erosion
Control Practices and
Structures for Farms
Terracing,
Crop
rotation
and Wind
Breaks
Wind Erosion
Factors that Decrease Wind Erosion
Cloddiness
Crop residue
Ridges
Barriers
Mass Wasting
The downslope movement of
unconsolidated Earth material
due to gravity.
Increasing Severity of Mass Wasting
Slump- quick downward
movement of a block of soil.
Rock
Slides
Creep-slow movement of soil down a
slope due to expansion and freezing.
Creep
Mudflows-very fast downward
movement of water and mud
The Stability of soil is reduced by:
1. Adding water to the material of a slope
2. Increasing the steepness of the slope
3. Removing material from the lower
part of the slope
4. Earthquakes
5. Removal of vegetation (increases
runoff)
Erosion
Created
Landforms
Mountains
erode to
peneplains
Sometimes monadnocks
(resistant knobs of rock) are
exposed.
Mountains erode finally to
plains
Plateaus (large high flat areas)
erode to form mesas (smaller
high table-like structures)
and buttes (small narrow
columns)
Engineering Solutions
Rock Nets
Soil Nailing
Avalanche
Barriers
(Switzerland)