Weathering, Erosion and Deposition Mechanical and Chemical

What Caused This?

What is Weathering? First step to forming soil and sedimentary rock Breakdown of rock into smaller pieces The smaller pieces do not move to a new location until erosion carries them away Many types of weathering

What is Mechanical Weathering? Breakdown of rock into smaller pieces without any change in the chemical composition of its minerals Sometimes called “physical” weathering Rock is torn apart by physical force, rather than by chemical breakdown Smaller pieces do not move to a new location until erosion carries them away

Mechanical - Ice Wedging Water fills joints of rocks and freezes Water expands 10% when it freezes, pushes rock apart Repeated freeze and thaw cycles over the years causes rock to break along joint

Frost Wedging

Mechanical - Exfoliation Exfoliation or unloading Rock breaks off into sheets along joints which are parallel to the surface Caused by expansion of rock due to uplift and removal of surface material that originally buried the rock

Mechanical - Thermal Thermal expansion Repeated daily heating and cooling of rock Heat causes expansion; cooling causes contraction Different minerals expand and contract at different rates causing the rock to split

Mechanical - Biotic Biotic – means life Weathering caused by living organisms Plant roots act as a wedge and widen cracks Other causes of biotic weathering are digging animals, microscopic plants and animals, algae and fungi.

What is Chemical Weathering? Breakdown of rock into smaller pieces because of change in the chemical composition of its minerals Chemical reactions break down the bonds holding the rocks together, causing them to fall apart Chemical weathering occurs in all types of rock Rock reacts with water, gases and solutions

Chemical - Oxidation Oxidation - oxygen combines with other elements in rocks to form new types of rock New substances are usually much softer than original, easier for other forces to break rock apart Causes a “rusting” of the rock, often causes a color change in the rock

Chemical - Carbonation Carbonation – Carbon dioxide (CO2) is dissolved in water making carbonic acid Weak acid is formed when CO2 in the air mixes with rain. This is the same acid found in soft drinks.  Acid is too weak to harm plants and animals but slowly causes feldspars and limestone to decompose

Last points…. On Weathering This may be on your test…..;-) In a volcanic eruption, the large amount of lave to the environment balances the force of weathering. Hydration and oxidation are examples of weathering.

Erosion The process by which water, ice, wind or gravity moves fragments of rock and soil.

Water Erosion Rivers, streams, and runoff

What Is Water Erosion? Water - most influential force in erosion Ability to move materials from one location to another over long distances The faster water moves in streams the larger objects it can pick up and transport Responsible for wearing away of rocks in rivers, lakes, and the oceans

What Is Wave Erosion? Waves - relentless pounding Erodes the softer, weaker parts of the rock first, leaving harder, more resistant rock behind Can take over 100 years to erode a rock to sand Energy of waves along with the chemical content of the water erodes the rock off the coastline

Mass Movements Landslides, mudslides, slump and creep landslide clip.mpeg

What Is Gravitational Erosion? Mass movement - downward movement of rock and sediments, mainly due to the force of gravity. Moves material from higher elevations to lower elevations where transporting agents like streams and glaciers can pick up the material and move it to lower elevations Process is occurring continuously on all slopes, some act very slowly while others occur very suddenly until equilibrium is reached Gravity related to the processes that change the land are both agents of erosion and deposition.

Ice Erosion Glaciers

What Is Glacial Erosion? Ice - moves and carries rocks, grinding the rocks beneath the glacier Glaciers pluck and abrade to cause erosion Plucking occurs when water enters cracks under the glacier, freezing, and breaking off pieces of rock that are then carried by the glacier. Abrasion cuts into the rock under the glacier, smoothing and polishing the rock surface A U-shaped mountain valley is evidence of the erosional ability of moving ice in a glacier.

What Is Bioerosion? Bioerosion - erosion of ocean rock by living organisms Caused by mollusks, polychaete worms, sponges, crustaceans, and fish Mechanisms of bioerosion include biotic boring, drilling, rasping, and scraping Bioerosion of coral reefs generates fine and white coral sand. The coral is converted to sand by internal bioeroders such as algae, fungi, bacteria, sponges, bivalves; external bioeroders include urchins and chiton. The actions of these organisms cause a great deal of material to be available for erosion.

Additional Erosion Information This may be on your test…. The desert ecoregion of Texas is likely to be most affected by erosion. A landslide carries many tons of rock from a hillside into a valley. All the plants are buried, the new plants that grow after the landslide will lack rich soil. Ripple marks that you see in the sand are made from wind erosion.

What is Deposition? Deposition - laying down of sediment that could have been transported by wind, water, or ice Process of erosion stops when the transported particles fall out of the transporting medium and settle on a surface Ability to carry material depends on an a balance of forces within the transporting medium If the velocity of the medium reduces or the resistance of the particles increases, the balance changes and cause deposition. Velocity can be reduced by large rocks, hills, vegetation,etc.

Wind Erosion and Deposotion

Deposition - Wind Wind velocity reductions can be related to variations in heating and cooling Wind can transport fine materials in suspension hundreds of km from its original source in the desert. Heavier material may be pulled along the ground. Material is eventually deposited when the wind changes direction or loses its strength. Obstacles, whether natural of man-made, will often decide where the deposition occurs and the nature of the feature formed.

Deposition - Water Stream water enters the lake and its velocity decreases. As velocity decreases, water's ability to carry sediments decreases Sediments carried by the stream are deposited where the slowing water can no longer move them. Largest particles are deposited near the shore. Increasingly smaller particles settle out farther from the shore where the water is calmer Occurs in streams, rivers, oceans, etc.

Deposition - Ice Glacial flows of ice - become slower if precipitation input is reduced or when the ice begins melting Deposits left by glaciers are called moraines and outwashes. Moraines are large chunks of broken rock left at the base and sides of the glacier as it melts and recedes. Finer material is carried in the rivers that form when the glacial ice melts. The deposits of these rivers look similar to normal river deposits and are called outwashes. Glacial rivers are usually white with fine silt known as "glacial milk".