Weathering & Erosion

Does the Earth’s surface

change over time?

What shapes the Earth’s

surface over time?

Weathering and Erosion

Weathering - processes at or near

Earth’s surface that cause rocks and

minerals to break down

Erosion - process of removing Earth

materials from their original sites

through weathering and transport

What evidence of weathering do

you see in this picture?

Types of Weathering

Mechanical (Physical) -

processes that break a

rock or mineral into

smaller pieces without

altering its

composition

Chemical - processes

that change the

chemical composition

of rocks and minerals

Mechanical Weathering

1. Abrasion/Scouring – wind & water

What evidence of weathering do

you see in this picture?

Why wasn’t this mass

of land weathered

away?

Mechanical Weathering 2. Frost wedging – water expands when it freezes

Frost Wedging

Mechanical Weathering 3. Exfoliation/Unloading

– As deeply buried rock is uplifted, pressure is

reduced and the rock breaks off into leaves or

sheets along joints

Enchanted Rock

Mechanical Weathering

4. Thermal Expansion/Contraction –

repeated, daily heating (expansion) and

cooling (contraction) of rock causes stress

along natural boundaries in the rock

Mechanical Weathering

5. Plant/Animal Activity – plant roots, animal

burrows

Mechanical Weathering

6. Crystal Growth – water evaporates

leaving minerals (salt) behind; crystals grow

and fracture the rock

Chemical Weathering • Rock reacts with water,

gases and solutions

which add or remove

elements from minerals

• Most caves formed

from limestone.

Chemical Weathering

1. Oxygen

– Iron combines with oxygen in the presence of water in a processes called oxidation. The product is rust.

Chemical Weathering

2. Carbon Dioxide

– CO2 dissolves in rain water and creates

carbonic acid which easily weathers limestone

and marble

1908 to 1969

Acid rain has eaten away this limestone statue

Chemical Weathering

3. Biological Activity

– Lichen that grow on rocks produce weak

acids that chemically weather rock

Erosion is caused by… 1. Water – Rain, Streams, Oceans, Ice

Erosion is Caused by…

2. Wind

Erosion is Caused by…

3. Gravity

Mass Wasting

• Movement of large amounts of material downhill

under the influence of gravity – Creep

– Solifluction

– Mudflow

– Earthflow

– Slump

– Rockfall

– Avalanche

Soil Creep

Creep

Slump

scarp

Slump near Fargo, ND

Mass Wasting in Haiti

Earthflow

Rockfalls, Yosemite, California

Triggers for rapid Mass Wasting

• Rain

• Over-steepening

– cutting at foot of slope

– piling on head of slope

• Deforestation / Devegetation

• Earthquakes