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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**