Title: Weathering Brown 24-25
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## Weathering Weathering vs. Erosion
Weathering
the breakup of rock due to exposure to processes that occur at Earths surface. How sediments form Erosion the removal, transportation, and deposition of sediment How sediments move 2How it started How its going The Old Man of the Mountain - New Hampshire. A victim of weathering and erosion Weathering
Weathering is the breakup of rock due to exposure to processes that occur at Earths surface. 2 types: 1. Physical 2. Chemical Physical Weathering
Physical Weathering splits or breaks rocks into smaller pieces of the same material without changing its composition. Creates sediments : Boulder (big)
Cobble Pebble Sand Silt Clay (small) 5 Types of Physical Weathering
1. Frost Wedging 2. Root Wedging 3. Animal Burrowing 4. Abrasion 5. Expansion cracking 1. Frost Wedging
1. Water gets into cracks 2. Water expands when it freezes, wedging the rock apart 3. Ice in the cracks melts, leaving behind broken pieces of the rock Potholes are frost wedging
Freezes in the winter, wedges out cracks of asphalt Melted water and rain carry away the pieces Passive-aggressive pothole garden 2. Root Wedging
1. Roots get into cracks in rock, expand as they grow 2. Wedges the rock apart 3. Animal Burrowing
Animals dig and burrow, breaking weak rock apart and creating more exposure for air, water and roots 4. Abrasion
Moving sediment in ice, water or wind scrapes against other rock and bits are broken off
Natures sandpaper
Question: Why are beach and river pebbles so round? water abrasion: Tumbling Action
Edges and corners have the most surface area = first to break off
Tumbling action is key (roll it around!)
Tumbling gives you rounded edges
Going from pointy edges to rounded corners Ice Abrasion: Glaciers make Striations
Striations : Parallel scratches in solid bedrock
Can show you the direction the glacier was moving! Wind Abrasion: Ventifacts
Ventifact : an abrasion-smoothed rock, shaped by wind-blown sediment; often has several faces Question: Why isnt a wind-abraded rock rounded like a river or wave-tumbled pebble?
> Ventifact with two faces
Ventifact 5. Expansion Cracking
Due to A) Mud cracks from Wetting and Drying 5. Expansion Cracking
Due to B) Columnar Joints from Heating and Cooling
Giants Causeway, Belfast, Northern Ireland Huge columnar joints in Iceland - CCHS trip 2017
Columnar joints piling up in a talus slope when they erode Due to C) Pressure release/Exfoliation
Exfoliate!
Exfoliation : the removal of outer layers
5. Expansion Cracking How pressure release/exfoliation works Some more views of exfoliation Remember: Physical weathering only changes the SIZE of a sediment. Now lets talk about Chemical weathering Chemical Weathering
Chemical Weathering changes a rocks minerals into different substances through chemical reactions
Oxidation of rock with iron-bearing minerals Carbonic acid weathering of tombstone 4 Types of Chemical Weathering
1. Oxidation 2. Hydrolysis 3. Dissolving 4. Carbonic Acid 1. Oxidation
Oxidation is a reaction of rock minerals with oxygen. Especially effective on iron minerals - oxidized minerals turn to yellow or orange RUST! Desert varnish
Desert varnish is a dark coating of oxidized iron and manganese on the outer surface of rocks Found often in the southwest Some ancient people would scratch artwork into the varnish pH of Rainwater
Rainwater is naturally slightly acidic with a pH of 5.6 Anything below 7 on the pH scale is considered acidic 2. Hydrolysis
Hydrolysis occurs when water reacts with minerals, breaking down the rocks into new compounds Most common example: feldspar minerals in granite rock turn to clay 3. Dissolving
Think: Sinkholes! 4. Carbonic acid
Carbon dioxide dissolves in rain water and creates carbonic acid This acid easily weathers the calcite found in marble and limestone rocks Also responsible for acid rain
Trees affected by carbonic acid rain
Carbonic acid weathering on marble George Washington statue 3 things that affect weathering rates:
1) Climate
Hotter = more chemical weathering
Wetter = more chemical weathering
Colder = more Physical weathering 2) Composition of the rock
Igneous/metamorphic = generally tougher 3) Amount of surface area/exposure
More surface area = more weathering (of both types) Great weathering example: Cleopatras Needle (Granite)
Based on the composition of this monument and climate of NYC, What specific type of weathering happened here? More information on the obelisks history and whats happening