Date post: | 18-May-2015 |
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Weathering
True or False: The Earth’s surface has stayed the same for thousands of years
True or False: The Earth’s surface has stayed the same for thousands of years
The Earth’s surface is always changing!
Weathering
takes place as rocks are broken down into smaller pieces over time by the effects of weather
What is Weathering?
•First step to forming soil and sedimentary rock.
•It is the breakdown of rocks into smallerpieces by physical and chemical processes.
•No movement is involved in weathering. •The smaller pieces do not move to a new
location until erosion carries them away.
• Breakdown of rock into smaller pieces without any change in the chemical composition of its minerals
– Sometimes called “physical” weathering– Rock is torn apart by physical force, rather
than by chemical breakdown.
– breakdown of rock by
physical means
What is Mechanical Weathering?
Mechanical Weathering
Ice wedging – water seeps into cracks in rocks, freezes and expands, and eventually cracks the rock
Ice Wedging – Water water seeps into cracks in rocks and
freezes.– Water expands 10% when it freezes, pushing
rock apart.– Repeated
freeze and
thaw cycles
over the
years causes
rock to break
Ice causes weathering
Abrasion – grinding and wearing down of rock surfaces by other rocks
Example: pebbles bump against each other in a river bottom
Example: rock bump against each other at the beach
Wind causes weathering
What evidence of weathering do you see in this
picture?
Why wasn’t this mass of
land weathered
away?
Biotic – means life– Weathering caused by living
organisms – Plant roots act as a wedge
and widen cracks.– Other causes of biotic
weathering:• burrowing animals • microscopic plants • animals• algae• fungi
Mechanical - Biotic
http://commons.wikimedia.org/wiki/File:Wedge_Rock_Turkey_Run_SP,_IN.jpg
Plants –
roots can crack rock
Mechanical Weathering – breakdown of rock by physical means
Animals – human traffic or worms and other animals digging
• Exfoliation or unloading --Rock breaks off into sheets along joints which are parallel to the surface.
-Caused by expansion of rock due to uplift and removal of surface material that originally buried the rock
Exfoliation
http://commons.wikimedia.org/wiki/File:Exfoliation_and_mass_movement.jpg
Thermal Expansion and Contraction – Repeated daily heating and cooling of rock
– Heat causes expansion; cooling causes contraction.
– Different minerals expand and contract at different rates causing the rock to split.
http://commons.wikimedia.org/wiki/File:Penmaen_Dewi-St_David%27s_Head_-_geograph.org.uk_-_1097950.jpg
• Chemical reactions break down the bonds holding the rocks together, causing them to fall apart.
– Chemical weathering occurs in all types of rock.
– Rock reacts with water, gases. and solutions.
What is Chemical Weathering?
Chemical Weathering •Chemical Reactions change rock composition.
They break down rock and minerals into new substances.•Chemical reactions happen
faster in warm, wet conditions
Chemical Weathering -.
4 Big Players1. Water : will dissolve rock, but it takes
1000’s of years.
Grand Canyon National Park, Arizona.
Big Bend National Park, West Texas
breaks down rock and minerals into new substances
Water causes weathering
What evidence of weathering do you see in this
picture?
Chemical Weathering
2. Carbon Dioxide: Dissolves in water to form a weak acid that reacts with calcite,
limestone, and marble
Ex. Acid precipitation (acid rain) breaks down rock.
breaks down rock and minerals into new substances
Carbonation – Carbon dioxide (CO2) is dissolved in water making carbonic acid
Chemical Weathering
There are acids in ground water that dissolve rock underground, creating caves.
Limestone being eroded by water that is high in carbonic acid (formed by carbon dioxide). Natural Bridge Caverns, San Antonio, TX.
breaks down rock and minerals into new substances
Chemical Weathering3. Organic matter decays,
makes water more acidic and reactive.Ex. Living things like algae, lichen, and
humans dissolve rock with the acids they contain.
Chemical Weathering
4. Oxygen: reacts with iron and makes rust (oxidation)
Oxidation – chemical reaction in which an element (iron) combines with oxygen to form an oxide (rust), rust = iron oxide
Monument Valley, Utah.Palo Duro Canyon, Texas