Transcript Chapter 12: Weathering

Chapter 12: Weathering
Chapter 12.1
Weathering – The breakup
of rock due to exposure to
process that occur on
Earth’s surface.
Mechanical Weathering - (disintegration)
the breakdown of rock into smaller pieces
(no change in composition)

Frost wedging occurs when water gets into
cracks of the rock and freezes when freezing
water occupies 10% more space.


Bare mountaintops are very susceptible forming
large sharp cornered boulder fields below
Pavement potholes are also caused by frost
wedging


Abrasion – caused by water wind and ice
scraping rocks, sand and pebbles against
one another.
Plants and animals



Roots grow and split rock
Animals make holes
Upward Expansion

Exfoliation – the release of pressure from overlying
rocks causes rocks underneath to expand upward
and crack.
Chemical weathering –
(decomposition)

Takes place when the rock’s minerals are
chemically changed into something different.
Usually caused by water or water vapor

Hydrolysis – reaction of water with other
substances



Usually increased in effect due to an acid in the
water
Carbonic acid – rainwater with CO2 has the
greatest effect on calcite (limestone) forming
underground caverns.
Acid rain – sulfur dioxide, nitrogen and carbon
dioxide released by industries react with water
in the air.

Oxidation - oxygen with other substances

Oxygen and iron will form a red iron oxide called
hematite
Rates of Weathering


The more the rock is broken down the faster
it weathers due to more surface area
exposed to water.
Composition of the rock


Sandstone with a silica (quartz) cement is more
durable than one with a calcite cement
Climate – a warm wet environment is more
conductive to both chemical and mechanical
weathering
Chapter 12.2
Soil – is made of loose
weathered rock material
with organic matter (dead
stuff)
How soil forms

Parent material – what the soil came from



Residual – from the under laying rock
Transported - brought in by rivers glaciers or wind
and deposited in the area.
Soil Profile – how the soil is layered in 3
distinct zones



A horizon – usually dark to light gray (topsoil)
B horizon – often red to brown (subsoil)
C horizon – partially weathered bedrock
Soil Composition – most
important factor is climate
p.266 in book.
Tropical forest soil – has a very
deep soil profile because of the
warm wet region it forms in.
Chapter 12.3


Mass Movement (The downward
transportation of weathered material by
gravity)
Erosion (the removal and transport of
material by natural agents)
Types of Mass Movements






Loose rock material continually moving downhill after it has
been weathered. May form a talus pile at the base of a steep
hill or mountain a talus pile can have a 40° slope.
Landslide - movement of bedrock and soil down slope.
Creep – a very slow down slope movement – fence post or
trees may move over time.
Slump – Blocks of land fall straight down.
Earth flow – Mass of weathered material and water move
down slope.
Mudflow – rapid movement of water with large amounts of
suspended clay and silt
Chapter 12.4
Soil as a resource

Less than 25% of earth’s land can be used
for crop growing.
Soil fertility – the ability of soil to
grow plants



Determined by the minerals, water and organic matter in the
soil
Soil Depletion
 Caused by crop plants using up the soils nutrients and not
being replaced because the organic material from the plants
is not replaced
 Fertilizers are used to replenish nutrients, but cause serious
environmental damages.
Salinization – When desert soils are artificially watered, the
water leaves behind minerals that accumulate over years and
the soils can no longer sustain crops.
Erosion and Soil Conservation

Types of Soil Conservation




Windbreaks – trees planted along fields to break
up the wind
Constructing terraces – to slow the water running
downhill
Contour forming – Plow with the contour lines to
reduce the speed of downhill water.
Strip farming – Alternate bare ground crops (corn)
with ground covering crops (alfalfa).