Weathering, Erosion, and SoilWhat type of rock is this, how can you tell?

Yosemite Valley, California

Mountains Carved by Glaciers

Grand Canyon, Arizona

Carved out by the Colorado River

Bryce Canyon, UtahAcidic Rainfall has worn away these rocks.The harder rocks remain standing… but for how long?

Weathering• Process by which rocks are broken down

due to exposure to processes occurring at the Earth’s surface

• Caused by– Water– Waves– Wind – Gravity– Glaciers

The 2 G’s and the 3 W’s

2 Types of Weathering• A. Mechanical Weathering also called

Physical weathering– Rock is broken down into smaller pieces

of the same material – (no change in composition)

• B. Chemical Weathering– The breakdown or decomposition of rock that occurs

when minerals are changed into different substances– (change in composition)

Mechanical/Physical Weathering1. Frost (Ice) Wedging

– Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes.

– Occurs where there are frequent freezes and thaws.

Explain what is happening.

• Frost/Ice Wedging Frost/Ice Wedging can cause can cause PotholesPotholes to form to form in pavementin pavement

Mechanical/Physical Weathering2. Abrasion

– The wearing away of rock material by grinding action

– Usually caused by sediment in Wind, Water, and Glaciers

Wind abrasion- sandblasting effect on stationary rocks as seen here in Arches National

Park

Hydraulic abrasion- water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania

Notice the rounded river rocks

Mechanical/Physical Weathering

3. Plants and Animals– Plant roots can split

rock– Also known as: “Root pry”

or “Root action”– Animals dig holes ,breaks

up rocks

Tree growingout of rock, ShenandoahNational ParkTree roots

also break up sidewalks

Mechanical/Physical Weathering

Exfoliation- gradual peeling of layers due to uplift and frost action, typical of granite domes like those in Yosemite N.P.

Exfoliation of Igneous rock

Chemical Weathering• Chemical Weathering

– The breakdown or decomposition of rock that occurs when minerals are changed into different substances

– (change in composition)

• Involves Water ,water vapor, Acids, and/or Oxygen

OO22

Chemical Weathering1. Hydrolysis• Carbonic Carbonic AcidAcid in in

water water dissolvesdissolves CalciteCalcite. This . This chemical chemical weathering can weathering can hollow out hollow out underground underground CavernsCaverns Limestone and Dolomite both

dissolve because they contain Calcite

Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone

Chemical Weathering2. Oxidation• Oxidation of minerals Oxidation of minerals

with with ironiron (magnetite, (magnetite, pyrite) results in the pyrite) results in the formation of formation of rustrust or or iron oxide.iron oxide.

• This is why This is why MarsMars is the red planetis the red planet

• Copper turns rocks Copper turns rocks greengreen

Rate of Weathering• How fast a rock weathers depends

on 3 factors:

–Surface area–Rock composition–Climate

Rate of Weathering• Surface area

– The greater the surface area, the faster the weathering rate

– There are more surfaces to be weathered

Rate of Weathering• Rock composition

– Some minerals are more resistant than others

– For example, quartz is more resistant (harder) than calcite

Quartz Calcite

Rate of Weathering• Climate (long term pattern of moisture and temperature)

– Weathering rates are faster in warm, wet climates

Desert vs. Rainforest

Erosion• Erosion

– The removal and transport of weathered materials by natural agents such as

– Caused by1. Glaciers 2. Running water 3. Gravity4. Wind5. Waves

Glaciers• Mass of compacted ice and snow

that moves under its own weight

Glaciers• Friction at the base of the glacier is reducedreduced

by a thin film of melt water.• Glaciers account for about 75% of the fresh fresh

water on Earthwater on Earth

• Glaciers can leave behind large boulders that are known as an erratic

Glaciers• Glaciers can move lots of sediment that

can carve striations (grooves) into rocks

These Striations show how glaciers moved

Glacial Deposits• Drift or Till - all sediment that is deposited by

glacial activity– Loess: fine powder, pulverized rock, that

blankets much of the northern mid-west– Moraine: ridge or pile of boulders, gravel, sand, and silt

left at the end of a glacier

Esker: type of outwash that accumulates in the channels and tunnels of a glacier

Glacial Landforms• Cirque

– Steep-walled bowl-shaped depression

• Horne: a pyramid shaped peak where 3 or more cirques meet

Glacial Landforms• Trough

–U-shaped valley, Glaciers carve U shaped valleys

Glacial Landforms• Hanging valley

– Straight drop-off at the end of a trough

• Arete– Narrow flat-topped

ridge that forms between two parallel troughs or cirques

Glacial Landforms• Moraine: Pile of mixed sediments that

have been carried and dropped by the glacier

Glacial Landforms• Eskers -Mounds of rock from melt tunnels

Streams and Rivers• Velocity - How fast the water moves• Gradient - The steepness, the slope that a river or

stream travels• Discharge - The amount of water that moves past a

certain point in a river in a given amount of time• If there is a steep gradient, high velocity, and

a large discharge, then Erosion will be severe!

• Rivers have energy to move lots of sediment, and even large boulders.

River stages affect:

Velocity,Gradient,

& discharge

which cause

Erosion

Seven Bends of the Shenandoah

Is the Shenandoah and old river or a young river?

River meandersBends in the river, shows how mature a river is.

Erosion-Mass Movement• The downward transportation of weathered

materials by gravity

Massive Landslide

Erosion-Mass Movement• Creep• Slump• Mudflow/Earthflow• Landslide/Rockslide

Erosion-Mass Movement: A large mass of sediment drops down!

Erosion-Mass Movement• Creep

– Very slow movement of earth material.– Caused by repeated freezing and thawing.

Sediments are loosened by expanding frost and contracting thaw.

Leaning fence posts and telephone poles are a sign of Creep.

Fence posts leaning due to creep

Erosion-Mass Movement• Slump

– Slow downward movement of a large mass of soil

Occurs when underlying sediments are weakened by heavy rainsCharacterized by a curved scar in the land surface.

Slump can cause road hazards

Erosion-Mass Movement• Mudflow/Earthflow

– Thick pastes of sediments that travel downhill at great speedsUsually occur in dry areas that get a large quantity of rain all at once

Leaves a cone shaped deposit

Mudflow in the Blue RidgeMooreman’s Gap near Charlottesville

Erosion-Mass Movement• Landslide/Rockslide

– Fast movement of large blocks of rock

Occurs in very steep vertical cliffs

Accelerated by ice wedging

At the bottom of an old rock slide in N.C. 2011

Wave Erosion• The crashing of waves on a shoreline

combined with storms continually shape the beach. This is a shoreline with erosion.

Wind and Waves• Wind moves

sand dunes at the beach and in the deserts.

Wind and Waves• Wind can carve out landscapes

as it carries sediment

Wind and Waves• Many storms combine water

and wind to cause significant erosion on landforms.

• Strong winds are capable of moving large amounts of sediment

Deposition: The process of dropping or depositing soil

and sediments.

Soil (dirt)• Soil includes loose weathered rock,

and organic material in which plant roots can grow

Soil Composition

Use this pie chart to answer the questions in your notes.

Soil Composition

What do the arrows mean?

Where soil forms• Residual soil

– The parent rock is the bedrock beneath the soil (the soil has not moved)

• Transported soil– Soil forms from parent material left by

winds, rivers, glaciers, or soil that was moved from its original location. This soil has been transported by erosion and deposition

Factors that affect Soil Composition• Parent material: What bedrock is it from?• Time: How long has it had to decompose?• Plants and animals: How have roots and

animals helped break up the rocks? Were there acid producing mosses that help break down the rocks (chemical weathering)?

• Topography: What is the shape of the landscape?

• Climate: Is it warm & wet? Were there glaciers present? Was there acid rain?

Soil Profile• Cross

section of soil layers revealing all soil horizons

Soil Horizon• A soil layer with physical and chemical

properties that are differentdifferent from adjacent layers

• O Horizon= organic material (humus)• A Horizon = topsoil• B Horizon = subsoil• C Horizon = partially weathered

parent material

Idealized Soil Profile

Humus:Dark organic matter in soil that is rich in nutrients.

Leaching: The removal of nutrients or toxins in soil as water passes through the layers.

Soil Texture• The size

of soil particles

Particle size ranges for sand, silt and clay

 Type of Mineral Particle   Size Range

 Sand  2.0 - 0.06 millimeters

 Silt  0.06 - 0.002 millimeters

 Clay  less than 0.002 millimeters

Large/ Coarse

Medium

Small/ Fine

EROSION

erosioerosionn

WeatheringWeathering

DepositioDepositionn

SedimentSedimentatiationon

to “settle”to “settle”