Rocks, Soils, Erosion, Weathering and DepositionStudy Guide with pictures added

Illustrated Earth and Environmental Science

Rocks, Soils, Erosion, Weathering and Deposition

• Weathering is the destructive processes by which materials at or near the Earth’s surface are changed in color, texture, composition, firmness or form. Weathering is the beginning of erosion. There are two types of weathering: mechanical or physical and; chemical.

What are the 2 types of weathering?

Physical/MechanicalChemical

Name six main processes of physical weathering.• mechanical – a physical change

in which rocks are broken down into different shapes and smaller pieces.• Six main processes can cause

mechanical weathering.• (1) Impact and abrasion- moving

materials can cause rocks to fracture, flake, or lose small particles. (www.geolocations.ws)

Mechanical weathering continued

• (2) frost action – water seeps into an opening or crack in a rock and then freezes when temperatures drop. Water expands when it freezes and causes rocks to break into pieces.

• (Weathering.wikispaces.com)

Weathering

• (3) Temperature- the cycle of heating and cooling of rocks causes a cycling of expansion and contraction that causes particles on the rock surface to crack or flake off.• (4) Organic activity- the roots of

plants can often loosen and change rock material.

Weathering

• (5) Gravity- can pull loosened rocks downhill, resulting in a landslide. This can cause rocks to break into smaller pieces.• (6) Exfoliation- rocks which form

under the surface form under pressure, which confines the rocks. When that pressure is released, the rock will expand. As it expands, the outer layers break free in sheets, and this is called exfoliation.

• Landslide at the Three Gorges Reservoir (www.international rivers.org)

• Exfoliation of rock• (www.patanography.wikispaces.com)

Chemical weathering- changes in the chemical makeup or mineral composition of rocks.

• Five main processes can cause chemical weathering.• (1) Water – can dissolve minerals

that are holding rocks together, or form acids when mixing with gases in the atmosphere to form acid rain (speeds up decomposition of rocks.) • Running water washes away the surface.

• Acid rain eats away at rock surface.

Chemical Weathering

• (2) Oxidation- oxygen can chemically combine with substances resulting in the formation of a new substance. Example: iron in rocks mixes with oxygen and forms rust.

• (www.wikispaces.com)

Chemical Weathering

• (3) Carbonation- carbon dioxide in the air can dissolve in rain, forming carbonic acid, which can dissolve certain rocks, such as limestone and feldspar.

• (www.pantography.wikispaces.com)

Chemical Weathering

• (4) Sulfuric acid- sulfur oxides can combine with water in the air, producing acid rain, which can chemically break down rocks, metals, and other materials.

Chemical weathering

• (5) Plant acids- some plants produce weak acids that can dissolve minerals in rocks(Ex: mosses)• As chemical changes take place,

minerals can be added or removed from rocks.

Erosion and deposition

• (1) erosion is the process by which weathered rock and soil are moved from one place to another.

• www.flickr.com• www.soil-net.com

Erosion and deposition

• (2) Erosion changes landscapes by wearing down mountains, filling in valleys, and making rivers appear and disappear.• (3) Deposition is the process by

which sediments are laid down in new locations.

Photo of landslide area, Annapurna region of Nepal, courtesy of Julien Lagarde on Flickr under Creative Commons

Erosion and deposition

(4) Weathering, erosion, and deposition act in a cycle to wear down and build up Earth’s surface.(5) The agents of erosion are gravity, wind, running water, glaciers, and waves.

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The five agents of erosion and their effects on landscape:

• 1. Gravity erosion or mass wasting is the downhill movement of sediments caused by gravity.

• (soilerosion 0918.wikispaces.com)

The five agents of erosion and their effects on landscape:

• a. Landslides- the tumbling of soil, rocks, and boulders down a slope.• b. Mudflows – usually occur after

heavy rains carrying large amounts of mud downhill.• c. Slump - materials such as rock

or soil on a steep slope move downhill as a coherent unit to decrease the slope angle of the land

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The five agents of erosion and their effects on landscape:

• d. Creep – the slow movement of sediments downslope, caused by repeated expansion and contraction of materials • Ex: freezing and melting, growth

and decay of roots, and burrowing animals

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The five agents of erosion and their effects on landscape:

• USGS

Running water – Runoff, Rivers and Streams

• 1. The amount of runoff is affected by the amount of rainfall, plant growth, and shape of the land.

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Running water – Runoff, Rivers and Streams

2. Urban storm water runoff effects water quality, (how clean or dirty) water quantity, (how much water) habitats, biological resources, public health and the aesthetic appearance )how pretty or ugly a place looks to us) of waterways.

a. After storms there is often a temporary increase in pollutants, toxins, and bacteria levels as material washes from lawns, pastures, and streets.

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http://www.mde.state.md.us/programs/Marylander/Pages/Stormwater.aspx

Running water – Runoff, Rivers and Streams

• b. Increased erosion and deposition results from large amounts of urban runoff which alters aquatic habitats.

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Running water – Runoff, Rivers and Streams

• c. Streams• 1. Streams usually cause erosion by

abrasion as sediments collide with rocks and wear down the rocks over time.• 2. Load – the soil particles and rocks

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Running water – Runoff, Rivers and Streams

• 3. If a stream flows first over a hard rock layer, then over a soft rock layer that is easily eroded, then a waterfall forms.

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Running water – Runoff, Rivers and Streams• 4. Downcutting represents downward

erosion of the stream channel. This happens when the stream energy (capacity to carry its load) exceeds the amount of material in the stream’s load. This digs out the bottom or stream bed, and causes valleys to be narrow and steep-sided (canyons and gorges).

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Running water – Runoff, Rivers and Streams• 5. Lateral erosion undermines part

of the bank or valley wall, leading to mass wasting and widening of the valley.• 6. Stream deposition results from

decreasing water velocity (the flow of the stream slows down) or from chemical changes. The coarsest material (larger rocks) is deposited first as water velocity (speed) decreases. Stream deposited material is called alluvium.

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Running water – Runoff, Rivers and Streams• River systems- streams that join

and form rivers, usually begin in mountains or hills.• 1. Larger streams flowing into a

main river are called tributaries.• 2. Eventually a river empties into

another river, a lake, or an ocean at the mouth.

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Running water – Runoff, Rivers and Streams• The drainage basin is all of the

area drained by a river and its channel.• a. drainage basins are separated

by divides (high ground between two drainage basins).• b. The Continental Divide is the

largest divide, running north and south (close to Denver, Colorado).

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North Carolina River basins

• Everyone lives in a river basin. Even if we don't live near the water, we live on land that drains to a river or estuary or lake, and our actions on that land affect water quality and quantity far downstream. There are 17 river basins in North Carolina, draining 52,337 square miles of surface and underground waters. The topography of each basin determines the area that it drains, and whether that water - from creeks, rivers, springs, and aquifers - flows into the Atlantic Ocean or Gulf of Mexico. (http://www.eenorthcarolina.org/riverbasins.html)

Running water – Runoff, Rivers and Streams• 4. Deposits are made by rivers

and are constantly changing the landscape of surrounding areas as sediments are deposited where a river curves, or meanders.• 5. Oxbow lakes are small lakes

formed from a U-shaped bend that erosion and deposition of sediments cuts off from the river. www.wsfcs.k12.nc.us350 × 433

Running water – Runoff, Rivers and Streams

Running water – Runoff, Rivers and Streams• 6. Deltas are formed as large

amounts of sediments are deposited at the mouth of a river.

• 7. Flood plains are flat areas on both sides of a mature river or stream. Fine sediments are deposited on flood plains after heavy rains or spring thaws. Larger sediments are deposited and form ridge-like deposits called levees.

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Running water – Runoff, Rivers and Streams

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Running water – Runoff, Rivers and Streams• Glacial ice erodes by abrasion

(rubbing) and plucking (picking up rocks) and wearing away underlying rocks.• As a glacier moves, it carries rock

materials (which are stuck in the ice) and wear down (erode) the land surface it passes over. This usually forms a U-shaped valley.

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Running water – Runoff, Rivers and Streams• The material deposited by a

glacier is called till. • The till left behind after a glacier

melts forms a ridge called a moraine.

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Running water – Runoff, Rivers and Streams• Glaciers can also form lakes by

leaving behind till that keeps water from flowing away from the area (Ex: the Great Lakes)

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Wind as an active agent of erosion in deserts, plowed fields, and beaches:

• Wind erodes Earth’s surface in two ways – abrasion and deflation.• Abrasion occurs when larger

particles carried by wind act as “sandblasters”, cutting and polishing rocks.• usgs

Wind as an agent of erosion

• Deflation occurs when loose materials such as clay, silt, and sand are carried away by the wind.

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Wind as an agent of erosion

• The amount of wind erosion is dependent upon four factors.• 1. Size of particles• 2. Speed of the wind• 3. Length of time the wind blows• 4. Resistance of rocks exposed to

wind

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Wind as an agent of erosion

• Deposits made by wind form dunes or loess deposits (layers of fine sand and silt deposited in an area).

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Ocean waves as agents of erosion

• Waves- their powerful force is constantly eroding and shaping shorelines.• Waves receive their energy from

winds that blow across the water surface. The size of a wave depends on how fast, how far, and how long the wind blows.

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Ocean waves as agents of erosion and deposition

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Ocean waves as agents of erosion and deposition

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Ocean waves as agents of erosion and deposition

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How to control erosion

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How to control erosion

Controlling erosion

Controlling erosionContour farming is a method of plowing along the contours of the land rather than up and down a slope. This creates furrows between crops to collect water.

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Construction sites can use sediment fences, temporary vegetation and grass covered drainage ditches to reduce erosion.

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How to control erosion

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http://water.usgs.gov/edu/gallery/impervious-areas-air.html

Sediments

• All causes of mechanical (physical) weathering result in the breaking down of rocks into smaller pieces called sediments.

• (www.flikr.com)

The 3 types of rocks.

• Igneous rocks form when molten rock cools and becomes solid. Molten rock is called magma when it is below the Earth’s surface and lava when it is above.

• https://www.windows2universe.org/earth/geology/sed_intro.html

• Sedimentary rocks contain clues about their past! Environments change over time. By looking at sedimentary rocks in an area you can figure out what the environment was like when those rocks were formed. Environmental features, like swamps, dunes, and oceans, contain different types of sediments. The type of sediment and the way it was deposited determines the kind of sedimentary rocks that will eventually be formed in a particular area. (https://www.windows2universe.org/newsletters/5_2012.html#C2)

• Metamorphic rocks are changed by heat and pressure• Any type of rock, can be metamorphosed. The rocks are

changed either in small areas of contact metamorphism or large areas of regional metamorphism. (http://www.windows2universe.org/earth/geology/meta_intro.html)

The difference between intrusive and extrusive igneous: Extrusive- hardens above ground Intrusive- hardens underground

Igneous rocks that form below the Earth’s surface are called intrusive igneous rocks (or plutonic). They form when magma enters an underground chamber, cools very slowly, and forms rocks full of large crystals(esprojects.wikispaces.com)

Igneous rocks that form above the Earth’s surface are called extrusive igneous rocks. These rocks, also called volcanic rocks, form when lava cools quickly at or above the Earth’s surface. (The rockcycle.wikispaces.com)

How are sedimentary rocks formed?

Compaction and cementation of sediments.

Do you see how the sediment that is collecting at the bottom of the California mountains in (A) looks like a fan from the left?

• This is called an alluvial fan! Alluvial fans form when sediment eroded from mountains is deposited on a valley floor like in (A). The rocks that are formed from an alluvial fan have large pieces of sediment that are not very round like the sediment in (B). (Courtesy of Martin Miller , University of Oregon and Earth Science World Imagebank. http://www.windows2universe.org/earth/geology/sed_alluvial.html)

the forces that form metamorphic rocks?

• Metamorphism usually happens where plates are coming together; rocks are heated and are under high pressure.• L.Gardiner/Windows Original• (https://www.windows2universe.org/earth/geology/meta_intro.html)

Humus is made of decaying organic matter.

Humus is dark, organic material that forms in soil when plant and animal matter decays.When plants drop leaves, twigs, and other material to the ground, it piles up. This material is called leaf litter. When animals die, their remains add to the litter. Over time, all this litter decomposes. This means it decays, or breaks down, into its most basic chemical elements. Many of these chemicals are important nutrients for the soil and organisms that depend on soil for life, such as plants.The thick brown or black substance that remains after most of the organic litter has decomposed is called humus. Earthworms often help mix humus with minerals in the soil. This leaf litter will eventually decompose and become nutrient-rich humus.Photograph by Iris Fong, MyShot (http://education.nationalgeographic.com/education/encyclopedia/humus/?ar_a=1)(http://www.madrimasd.org/blogs/universo/2007/10/02/75038)

It takes soil hundreds of years to form from parent rock.

• Soils- soil is made of loose, weathered rock and organic material in which plants with root can grow. The rock material is composed sand, silt, and clay.

• Parent material- the material from which a soil is formed.• Residual Soil- soil that has the bedrock beneath the soil

as a parent material• Transported Soil- soild formed from deposits left by

winds, rivers, and glaciers.• A-Horizaon (Top Soil)- darkest color due to organic

material.• B-Horizaon (Subsoil)- 1) clay is washed to the subsoil• 2) May contain soluble minerals, such as calcium and

magnesium carbonates• 3) color is usually red- brown from iron oxides that form

above and wash down• C-Horizon- Made of slightly weathered parent material

(rock

. Soil is important to living things because plant roots need soil to grow.

. Name the 3 basic soil particles.

• The rock material is composed sand, silt, and clay. (http://www.hort.purdue.edu/ext/loam.html)

• Sand Silt Clay

What is loamy soil?

• A mixture of sand, clay and humus• A loamy soil is one that

combines all three of these types of particles in relatively equal amounts. Loamy soil is ideal for most garden plants because it holds plenty of moisture but also drains well so that sufficient air can reach the roots. (http://www.hort.purdue.edu/ext/loam.html)

The layers of a soil profile.

• Organic layer• Topsoil• Weathered parent material• Un-weathered Parent material

. The five causes of soil mismanagement are:• Clearing vegetation• Plants planted in the wrong location• Overuse of pesticides and fertilizers• Pollution of cars and factories• Compaction from animals roads and construction

Overuse of pesticides

Clearing vegetation

Planting in wrong location

Pollution of cars and factories