Transcript Chapter 23: Earth`s Changing Surface

Chapter 23: Earth’s
Changing Surface
Objectives:
•What is weathering & erosion?
•Give examples of mechanical and chemical weathering.
•How do weathering & erosion change Earth’s surface?
•How do you “read” sedimentary rocks that are formed as a
result of erosion and deposition?
Weathering
Weathering by wind and water causes rocks
to break apart into smaller pieces or
SEDIMENTS (SEDIMENT = END PRODUCT).
Types of Weathering
1. Mechanical – Rocks are broken apart
physically
Examples of Mechanical Weathering
1A. Frost Wedging
•Water seeps into
cracks of rocks and
freezes when temps.
drop.
•Ice expands and
wedges apart rocks
Frost Wedging creates rock spires and pot holes.
Frost wedging happens in environment where
temperatures alternate between hot and cold or where
there are seasons
Hoodoos were created by frost wedging over a long period of time
Examples Mechanical Weathering
1B. Abrasion =
Wind or water
SCRAPES the
surface of rock
to break it up.
(sand blasting)
Examples of Mechanical Weathering
1 C. Plant roots – help break apart rocks
Chemical Weathering
Rocks containing calcium (limestone,
marble, etc.) dissolve in acidic water.
Rain can be acidic because of dissolved
carbon dioxide (carbonic acid)
Example:
Caves form in
limestone rocks.
Water seeps through
ground and dissolves
rock to form caverns.
Erosion
Erosion is when the sediments (made by
weathering) are carried away to a new
location by wind or water.
AGENTS OF
EROSION:
1. Water
2. Wind
3. Gravity
Mass Movements= Erosion w/ help
of gravity. Once weathering has
broken rock up, gravity can move
rocks down slopes! (H2O usu. helps)
• Land slides – rapid, large amounts of
rock & soil
• Mudflows – rapid, large amounts of soil,
sediments & water
• Creep – gradual, soil moves down slope
(alt. freezing & cold temps)
• Slump – rapid, small amount of hillside
move down a “step” (Wet soil)
Types of Mass Movement (aka, mass wasting)
Sediments are deposited in layers and
cement into new layers of sedimentary rock
Layer A was laid down first.
Then layer B.
Layer I is the most recent.
“Story of Rocks”
•Lower layers came first.
•Index fossils are used to
guess the age of rocks.
•Magma intrusions come
after the layers they cross
through.
•Folding can change the
direction of layers.