Weathering & Erosion

Weathering & Erosion

Weathering • The breaking down of rock.

Physical (or mechanical) Weathering Physical (or mechanical) breakdown: it is the mechanical breakdown of rock or minerals. It only breaks the rock or mineral into smaller pieces, the composition of the material is NOT changed!!

Physical (Mechanical) Weathering • There are several different types of physical weathering: • 1.) Frost or Ice Wedging –The breakingdown of rock by the force exerted by water expanding as it freezes into ice.

Water expands as it freezes, this breaks the rock into angular fragments.

This occurs A LOT in Western New York –because we have alternating freezing and thawing of moisture in rock openings, causing rock disintegration, in other words POTHOLES. • This will ONLY occur in areas where the temperature alternates above freezing and below freezing! Frost Wedging animation

2.) Exfoliation Exfoliation – Erosion of upper rock causes underlying rock to expand resulting in cracking and peeling of rock in slabs. • Think of onion skin layers and peeling them off.

PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY OF ROCK due to unloading (reduced pressure at earth’s surface) or fluctuations in temperature. Rocks expand and crack

PHYSICAL WEATHERING - EXFOLIATION

Stone Mountain, Georgia- exfoliation has caused an overall rounded shape to the mountain.

3.) Organic Activity (plant and animal) Organic Activity – plant roots or animals like burrowing worms can cause rock to breakdown.

PHYSICAL WEATHERING – ROOT ACTION PLANT ROOTS UPLIFT AND FRACTURE ROCK

4.) Wetting/Drying Wetting and Drying - addition of water to mineral structure causes structure to expand. Mudcracks form from the wetting and drying of clay material.

Important! What happens to the erosion rate when you increase the surface area? • Physical weathering increases the surface area of rocks/minerals. • Taking a rock/mineral and breaking it up into smaller pieces causes it to take up more space (surface area) and will eventually increase the rate of chemical weathering to occur.

Physical Weathering occurs Let’s Work This Through! Starting Volume:_______________ Volume:________________________ Total Surface Area:____________ Surface Area:__________________ (2 feet)3 = 8ft3 (2 feet)3 = 8ft3 6 x (2ft)2=24ft2 6 x (1foot)2 x 8 = 48ft2

Chemical Weathering Chemical weathering: is the decomposition of material. The composition IS Changed! Oxidation: iron turns RED!

Chemical Weathering

1.) Hydrolysis Hydrolysis – the chemical reaction between water and other substances. Silicate minerals will often form clay from this process. Kaolin mine, central Georgia (feldspar weathered into clay by hydrolosis)

Hydrolysis cont… Halite, gypsum, and limestone are most susceptible to becoming weathered by water, and most compounds are at least slightly soluble in water, so water is called the universal solvent. Chemically Weathered Limestone

2.) Carbonation Carbonation (Carbonic Acid) – dissolving of substances by acids in water often leaving insoluble remains. Carbonic Acid can devastate rocks made of calcite. Rocks such as limestone and dolomite can be entirely dissolved, leaving extensive caverns.

Caves formed from Carbonation

3.) Oxidation Oxidation – chemical reaction of a substance with oxygen causing a rust material to form. Note: Most rocks/minerals containing iron will appear RED in color after an oxidation reaction. Oxidation of Sandstone

Climate and Weathering • Climate plays a very important role in weathering. • The temperature and amount of moisture influences the type of weathering that will occur. • Warm and wet climates produce mostly chemical weathering. Never any frost wedging. • Cool and slightly wet climates produce mostly physical weathering.

Factors Effecting Weathering Rate

Cleopatra’s Needle 80 years later: look what’s happened Cleopatra’s Needle in Egypt: warm, dry climate, little to not weathering occurs. Cleopatra’s Needle was moved to New York and has weathered significantly on only 80 years due to: cold and wet climate

Weathering and Resistance • The harder the rock or mineral is, the more resistant it will be to weathering. • Any rock with quartz will be quite resistant due to quartz’s hardness. • Rocks made mostly of calcite, a very soft mineral, will be easily weathered.

WHAT KIND OF CLIMATE SUPPORTS WEATHERING? HIGH PPT ↑ ↑ ↑ ↑ ↑ ↑ ↑ LOW PPT COLD→→→→→→→→→→ HOT

CLIMATE CONTROLS WEATHERING • PHYSICAL WEATHERING: COLD AND MOIST ALTERNATE FREEZE / THAW • CHEMICAL WEATHERING: WARM AND MOIST IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERING

WHICH LAYER IS MORE RESISTANT TO WEATHERING?LEAST RESISTANT? D A C B

THE END PRODUCTS OF WEATHERING The end products of weathering are sediments. They can be pieces that range in size from boulders to silt…

Do I have to say it?

Or they can be ions in solution

WEATHERING SUMMARY • WEATHERING IS THE BREAKDOWN OF ROCK INTO SEDIMENTS • PHYSICAL WEATHERING – INCREASES SURFACE AREA - COLD/HUMID CLIMATE • CHEMICAL WEATHERING – WARM/HUMID CLIMATE • IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT

Erosion the removal and/or transport of material by 5 possible agents: running water, glaciers, waves, wind, and gravity.

Five Agents of Erosion are: 1- Water 2- Wind 3- Waves 4- Glaciers 5- Gravity A good way to remember these are: www.gg

We also have to remember that humans and animals may also play a part in erosion

Weathering & Erosion