Weathering What is Weathering? - PowerPoint Presentation

Slide1

Weathering

What is Weathering?

Weathering can be defined as any

chemical or mechanical process by which rocks exposed to weather undergo changes in character or are broken down into smaller pieces

.

Mechanical Weathering

Mechanical Weathering

is a type of weathering that

breaks down rocks into smaller pieces without changing the chemical composition of the rock.

For example, Granite can be broken down into smaller pieces, but the smaller pieces are still Granite.

Agents of Mechanical Weathering

Frost Wedging

– When water freezes

in the

cracks of rocks

causing them to

expand and break the rock

.

The

products

of

f

rost

w

edging

are

large piles of rocks

called

talus

.

Frost Wedging

Frost Wedging

Talus produced by Frost Wedging

Release of Pressure

Unloading and Exfoliation

– When large sections of rock buried

underneath the ground are

exposed at the surface

, enormous amounts of

pressure

are

released

. This release of pressure is referred to as

unloading.After unloading, the rocks begin to flake off in sections like an onion. This is referred to as exfoliation.

Unloading and Exfoliation

Unloading and Exfoliation

Giant Slabs of rock flake off

As a result of Unloading and

Exfoliation- Right- STONE MOUNTA

IN, GA

Agents of Mechanical Weathering

Biologic Activity

– Weathering that occurs as a result of the

actions of living organisms like

plants and animals

.

Plants

often cause mechanical weathering when their

roots penetrate

down into the

cracks of rocks.When the

roots grow they expand.Animals burrowing into the ground can also create cracks in the rocks.

Animal Actions

Roots penetrating the cracks in rocks

Gophers and Earthworms Burrowing

Also contribute to Mechanical Weathering

Root Wedging

Abrasion

Abrasion is the grinding, scraping, rubbing, or scratching of rock particles against other rock particles.

Agents of Abrasion:

Wind

Water

Glaciers

Waves

Wind

Water

Waves

Glacier

Chemical Weathering

When rocks that weather

change their composition

into a new type of rock

, this is referred to as

chemical weathering

.

Chemical Weathering

The

three main types

of chemical weathering.Carbonation

occurs when

c

arbonic

a

cid

(H

2CO3)

dissolves minerals in rocks.Hydrolysis occurs when hydrogen in water dissolves minerals in rocks.Oxidation occurs when oxygen reacts with minerals in rocks.

Chemical Weathering

Examples

of each type include.

Carbonation occurs when acid rain

(carbonic acid)

dissolves limestone bedrock

to produce

caves

.

Hydrolysis

transforms feldspar (in granite), to produce

clay sediments.Oxidation transforms rocks with iron (like basalt and gabbro) into hematite (rust).

Chemical Weathering

Oxidation of Mafic/Basaltic Rocks

To produce the mineral Hematite

Weathering of

Granite to

Produce clay

sediments

Carbonic Acid dissolves limestone

To produce caverns

Rate of Weathering

The most important factors that affect the rate (time) of weathering are

Surface Area

-

More cracks

means

more surface area

, more surface area means

more weathering

.

Composition –

Certain minerals are more resistant to weathering than others. Quartz for example is more resistant to weathering than calcite.

Rate of Weathering

How Weathering Affects the

Surface Area

and the Rate of Weathering

Rate of Weathering

Climate

– Hot, humid

climates

have

a

fast

rate of weathering. Cold, dry climates have a

slow rate of weathering.Vegetation – Places with more vegetation tend to have a higher rate of weathering because certain plants help produce acids that help speed up the rate of weathering.

Rate of Weathering Varies depending upon the Climate