Aim: How can weathering change rock?

Do now: Look at these rock formations.

How do you think they were formed?

Weathering

Weathering

• Weathering is the process of breaking

down of the materials of Earth’s crust into

smaller pieces.

Two Types Of Weathering:

1) Physical weathering is breaking rock by force.

• The rock material is the same but smaller.

– Cracking

– Pounding

– Scraping

2) Chemical weathering is where the rock material

is changed into another substance by reacting

with a chemical.

Physical Weathering

• Process by which rocks are broken down

into smaller pieces by external conditions.

• Types of Physical weathering

– Frost heaving and Frost wedging

– Plant roots

– Friction and impact

– Burrowing of animals

– Temperature changes

Frost Wedging

•Frost wedging is the process of

splitting rock as the results of

water expanding inside a crack

as it freezes.

•The stress created by the

expanding ice forces the crack to

widen.

•As the crack widens, more water

fills the crack, forcing the crack to

widen as this new water freezes

Frost Heaving

•Frost heaving is similar

to Ice wedging except

ice form under rocks

causing the rock to

move out of its original

position.

•This could cause

erosion under the rock

to occur.

Plant Roots •Sometimes seeds fall into cracks of

rocks.

•When the seed grows, its roots

secret a chemical which breakdown

rocks, so that the root have room to

grow.

Friction and Repeated Impact

•Friction and repeated impact can occur in

three ways.

•Moving water

•Moving Ice

•Move air (wind)

Friction and Repeated Impact -

Water 1. As water moves across rock,

the water molecules rub

against the rock, slowly

grinding the rock down.

2. Sometimes hard materials

are mixed in with moving

water. These materials may

smash against rock, chipping

away at it.

3. Since water is heavy,

sometimes the pressure of

water is enough to push

through rock.

Friction and Repeated Impact -

Ice • In very cold regions of the world, glaciers form as the

results of thousands of years of snow pile up onto itself.

• These thick sheet on ice are very heavy and begin to

move down mountain sides.

• As they move material trapped in the ice begin to move

with the glacier- grinding along the bottom against the

ground. Scraping at the rock.

Friction and Repeated Impact -

Wind 1. As wind moves across

rock, the air molecules

rub against the rock,

slowly grinding the rock

down.

2. Sometimes hard

materials (like sand) are

mixed in with moving air.

These materials may

smash against rock,

chipping away at it.

Burrowing of Animals

Many animal will dig

holes and tunnels in

the ground for

shelter and a way to

move safely from

one place to

another.

Earthworms secrete

a chemical with help

breakdown rocks so

they can move

through the ground.

Chemical Weathering

• The process that breaks down rock

through chemical changes.

• The agents of chemical weathering

– Water

– Oxygen

– Carbon dioxide

– Living organisms

– Acid rain

Water

• Water weathers rock by dissolving it

Water - Caves

• Caves are the results of

water dissolving limestone

resulting from underground

streams or seepage from

the surface.

Water - Sinkholes • Sinkholes are the results

of the roof of a cave

collapsing.

Oxygen

• Iron combines with oxygen in the presence of water in a processes called oxidation

• The product of oxidation is rust

Carbon Dioxide

• CO2 dissolves in rain water and creates

carbonic acid

• Carbonic acid easily weathers limestone

and marble

Living Organisms

• Lichens that grow on rocks produce weak

acids that chemically weather rock

Acid Rain

• Compounds from burning coal, oil and gas

react chemically with water forming acids.

• Acid rain causes very rapid chemical

weathering

Rates of weathering will be influenced by

3 main factors:

1. Surface area exposed

2. The type of mineral the rock is made of

3. Environmental Climate

Rates of weathering will be influenced

by: Surface area exposed

Surface area exposed - weathering only

occurs on the surface of rock. The more

surface exposed, the faster the weathering

will occur.

A full, solid block has the least surface area. The interior is safe from exposure.

A smashed piece has greatest surface area exposed. The interior can now be attacked.

• Mineral composition- some minerals are

more resistant than others.

• Some materials are very hard, so they

ware down slowly.

• Some materials are very soft, so they ware

down quickly. • ex.:Quartz is resistant to chemical and physical

weathering.

Rates of weathering will be influenced

by: Mineral composition

• Climatic Conditions:

– Cold and/or dry climates favor physical

weathering.

– Warm and wet climates favor chemical

weathering.

– Frost action works best in areas where the

temperature fluctuates wildly.

Rates of Weathering will depend

on: Climatic Conditions

Soil - The product of weathering

• Soil- rocks, minerals (mainly sand and

clay), and organic material (regolith and

organic matter)

• Soil forms layers of different

characteristics called horizons.

• Soil formation is important because

complex plants can grow.

Erosion

Erosion • The process by which water, ice, wind or

gravity moves fragments of rock and soil

from one area to another..

LANDSCAPES ARE SHAPED BY

EROSION OR DEPOSITION

Erosion – The transport of sediment. Occurs

naturally, wind water or gravity.

Deposition – The drop off of sediment to a

new location.

Water Erosion • Rivers, streams, and runoff cut into rock

and soil creating depression in the

surface.

• Fast moving currents move materials to

areas where the current is slower, there by

dropping them at a new location.

Evidence of water erosion • Rock and land that are cut by water tend to have

deep V-shaped valleys.

• This is because usually in the middle of a stream or

river, the water is moving much faster than the

water on the sides.

• The faster the water moves, the faster it erodes

rock.

• Where currents slow down, sediments are dropped.

• Sediment is arranged or sorted with the largest

particles on the bottom layer and the smallest

particles on the top layer.

Evidence of water erosion

OCEAN - EROSION

• CLIFFS

• The Ocean is

constantly moving.

• Tides causes the

oceans to rise and

lower, changing the

environment that the

rock is exposed to.

• Waves repeatedly

pound against rock,

causing them to chip

and break.

Ice Erosion • As Glaciers form

materials get trapped

in the ice and as the

glacier moves so

does the trapped

materials (sand, rocks

boulders)

Evidence of Ice Erosion • Glaciers are very heavy.

• In general, Glaciers move very slow and

uniformed.

• Glaciers cut U- shaped valleys.

• When glaciers begin to melt, large boulder are

released and deposited.

• Deep parallel groves are cut into rock in the

direction of glacier movement.

• The sediment is unorganized or unsorted. Large

and small particles are mixed together.

Evidence of Ice Erosion

Wind Erosion • As strong wind blows across

land and rock, some

materials are lifted up and

move to other areas (sand,

rocks).

• When the wind calms down,

these material drop down.

Evidence of Wind Erosion • Wind moves in variable

speeds. Sometimes very

fast and sometimes not

at all.

• This difference in wind

speed can cause unique

rock formations.

Mass Movements

• Landslides, mudslides,

slump and creep.

• Landslides occur as the

result of a layer of soil or

soil under ground

becomes unstable.

• The weight of the surface

material becomes too

great, causing a large

section of land to shift

downhill.

landslide clip.mpeg

Possible Mass Movement

Problem • http://www.youtube.com/watch?v=3jlaiJRw

U6Q&feature=related

Deposition

• What does deposition look

like?

How is Sediment Deposited? • Energy is needed to move

sediments from one area to

another.

• The more energy, the larger the

sediment that can be moved.

• Once the energy begins to

decrease, larger sediments

begin to settle.

GLACIAL DEPOSITS

Sediments deposited as a glacier melted

Erratic boulder - there are no other rocks like it the area.

Moraine – sediments left behind from a glacier are unsorted (different sizes)

GROUND WATER DEPOSITS

Stalactites – (rock icicles)

• Form from dissolved minerals sediment that drip from cave ceilings.

• They form from the top and grow toward the floor.

Stalagmites – (upside down rockcicles)

• Sediments deposit as undeposited minerals drip from stalactites.

• Take hundreds of years to form.

WIND DEPOSITS Sediment eroded by wind and deposited in

new location.

SAND - DUNES CLAY - LOESS

OCEAN DEPOSITS • Ocean currents can

move sand from one

area of beach to

another.

• Creating sand bars,

new beach and even

islands.