Download 3.1 - Weathering Define mechanical and chemical weathering

3.1 - WEATHERING
1.
Define mechanical and chemical weathering.
2.
Identify agents of weathering.
3.
Discuss factors that influence weathering.
FOOTPRINTS ON THE MOON

Footprints left on the Moon from one of the Apollo
missions from 1963-1972.
Why will these
footprints always
exist on the moon?
WHAT IS WEATHERING?

Process that breaks solid rock into sediments

Himalayan Mtns.

Appalachian Mtns
2 MAIN TYPES OF WEATHERING
1.
2.
Mechanical Weathering
Chemical Weathering
MECHANICAL WEATHERING


Breaks rocks down into smaller pieces without
changing the chemical composition of the rock
Some Agents of Mechanical Weathering
1.
2.
3.
4.
Ice Wedging
Abrasion
Biological Weathering: Plants and Animals
Human Activities
ICE WEDGING
ABRASION



Caused by rocks bumping into each other
Makes rocks with sharp or jagged edges smooth and round
Agents of Abrasion:
1. Gravity
2. Moving Water
3. Wind
4. Glaciers
MOVING WATER

causes abrasion as particles in the water
collide and bump against one another.
WIND

Strong winds carrying pieces of sand can sandblast
surfaces.
http://education-portal.com/academy/lesson/wind-action-effects-on-thedesert-landscape.html#lesson
GLACIERS


Ice in glaciers carries many bits and pieces of rock.
Rocks embedded at the bottom of the glacier scrape
against the rocks below.
The Burren
County Clare, Ireland
BIOLOGICAL WEATHERING: PLANTS

A plant’s roots can grow into a crack or fracture in
rock and gradually grow larger, wedging open the
crack.
BIOLOGICAL WEATHERING: ANIMALS
HUMAN ACTIVITIES

Human activities are responsible for enormous amounts
of mechanical weathering, by digging or blasting intorock
to build homes, roads, subways, or to quarry stone.
CHEMICAL WEATHERING
works through chemical reactions that cause
changes in the minerals of rock.
 Agents of Chemical Weathering

1.
2.
3.
4.
Water (Hydrolysis)
Carbon dioxide (Carbonation)
Oxygen (oxidation)
Acid Rain
WATER


Hydrolysis = water reacts with compounds in rock causing
the compounds to dissolve/break apart
Leaching = occurs as water breaks down compounds in
rock and carries ions away
Check out this animation of how water dissolves salt:
http://www.northland.cc.mn.us/biology/Biology1111/animations/diss
olve.html
CARBON DIOXIDE



Carbon dioxide (CO2) combines with water as raindrops
fall through the atmosphere to form carbonic acid.
Carbonic acid dissolves rocks.
Many limestone caves have been formed by the action of
carbonic acid.
OXYGEN



Oxidation is a chemical reaction that takes place when
oxygen reacts with another element.
Minerals that are rich in iron break down as the iron
oxidizes and forms new compounds.
Iron oxide (rust) produces the red color in soils.
ACID RAIN


Pollutants, such as sulfur and nitrogen, from fossil
fuel burning, create sulfuric acid and nitric acid.
These acids react with water in the atmosphere to
form acid rain.
FACTORS THAT AFFECT THE RATE OF
WEATHERING
Exposure to the Atmosphere
 Composition of Rock
 Climate

EXPOSURE TO THE ATMOSPHERE


Rocks exposed to the atmosphere weather faster
than rocks that remain unexposed.
Mechanical weathering can speed up the rate of
chemical weathering by increasing the surface
area of rock.
COMPOSITION OF ROCK


Different rock types weather at different rates.
 Igneous rocks (especially intrusive) weather slowly
because it is hard for water to penetrate them.
(ex.
Granite)
 Other types of rock, such as limestone, are easily
weathered because they dissolve in weak acids.
Different minerals weather at different rates.
 Some minerals dissolve easily in water while others do
not.
CLIMATE
Climate is weather averaged over a long
period of time.
 Chemical weathering increases as:

Temperature increases:
 Chemical reactions proceed more rapidly at
higher temperatures.
 Precipitation increases:
 Since water participates in both mechanical
and chemical weathering, more water strongly
increases weathering.

Which type of climate do you think has a higher rate of
weathering?