WeatheringErosion, Rivers and Glaciers

WeatheringThe breakup of rock due to exposure to

the atmosphereCan be Physical/Mechanical or Chemical

I. Physical/Mechanical WeatheringWhen rocks are split or broken into smaller

pieces of the same material without changing the composition

EXAMPLES:Ice/frost wedging causes potholesRoot wedging lifts up sidewalksWetting and drying

Ice/Frost Wedging

Root Wedging

II. Chemical Weathering Decomposition of rock that takes place when the

rock’s minerals are changed into new substances EXAMPLES:

Hydrolysis is the chemical reaction of water with rocks

Oxidation is the reaction of oxygen and other substances: causes rusting

Carbonic Acid: dissolved carbon dioxide in water, changes minerals into clay minerals

III. Acid PrecipitationRain, snow, or sleet mixes with sulfuric

and/or nitrogen compounds in pollutionResults in sulfuric and/or carbonic acidNatural rain has a pH of about 5.7 due to

natural CO2 in the atmosphere

Acid rain has a pH of between 4 and 5

III. Acid Precipitation

Cleopatra’s Needle, Central Park NYC

Do Now:

What is it called when oxygen reacts with elements of rocks?

What is carbonic acid?

Obj: LWBAT continue your understanding of the processes of weathering.

IV. ErosionThe removal and transportation of weathered

materials by running water/waves, wind and ice (glaciers)

Carries and deposits sedimentCan form structures such as deltas, fins, and

sandstone arches

IV. Erosion

Sandstone Fins, Arches National Park, UT

Sandstone Arches, Arches National Park, UT

V. Rate of Weathering Weathering is affected by:

1. Amount of rock exposed at the surface2. Type of rock

1. Igneous & Metamorphic – more resistant2. Sedimentary – least resistant

3. Climatea. Hot/Cold and dry – more physical weatheringb. Warm and moist – more chemical weathering

VI. RIVERSA. Running water

1. Comes from water cycle (precipitation to runoff)

2. Moves downhill from force of gravity

B. Breaking down of sediment and rock1. Mechanical

a. Abrasion – rubbing of rocks against stream bed

2. Chemicala. Rain and spring melt lowers pH of lakes – “Acid Shock”

b. Can be neutralized by dissolving soluble carbonate rocks (ex. Limestone)

VI. RIVERS (con’t)

C. Erosion – water carries rock and sediment downstream

1. Solution – minerals dissolved in water2. Suspension – small particles carried in water flow

(“muddy water”)3. Bed load – boulders and pebbles pushed along

bottom of stream4. Delta – fan shaped deposit of silt and sand at end

of river

Deltaand not the force

VI. RIVERS (con’t)

D. Carrying Power1. Amount of sediment and size of particles2. Depends on speed and discharge

a. Increases as speed and discharge increaseb. Discharge – volume of water flowing past a certain point

E. Speed of streama. Depends on steepness of stream bedb. Steeper = fasterc. “Graded River” – even/consistent slope

E. Stages of Stream Development

Youth Stage

•Steep V-shaped valley

•Lowest discharge

•Greatest speed

E. Stages of Stream Development

Mature Stage

•Wide valley

•Erosion of valley walls

•Floodplain developing

E. Stages of Stream DevelopmentOld-age Stage

•Valley walls completely eroded

•Large flat floodplain

•Meanders and oxbow lakes

•Maximum discharge

Oxbow lake

floodplain

Tributary streams

Meanders

Colorado River,

Grand Canyon, AZ

F. Watersheds

Watershed – the entire land area drained by a river and its tributaries

Largest watershed in the US is the Mississippi

VII. GlaciersA. 2 types:

1. Valley aka Alpine Glaciera. Long, slow-moving

wedge-shaped stream of ice

2. Continental Glaciera. Large sheets of ice

covering a large part of a continent Ice Sheet on 

Ellesmere Island, Canada

VII. GlaciersB. Largest Glaciers

1. Antarcticaa. Continental Glacier

2. Last ice agea. ~18,000 years ago

b. Ice covered Great Lakes and reached to IN, OH and NJ

c. Sea levels drop

Great Lakes NJ

C. Glacial Features

Firn – granular snow atop a glacier

Crevasses – deep cracks in the ice

Snow line – lowest level of snow in summer

Ice front – edge of a glacier

**glaciers carve U-Shaped valleys**