Weathering

Do Now:Weathering1. How does the sun play a role in weathering?

2. Describe the similarity between the ways tree roots and ice mechanically weather rock. EQ- How do rocks and minerals break down?EQ- How do rocks and minerals break down?GPS: S6E5. Students will investigate the scientific view of how the earths surface is formed d. Describe processes that change rocks and the surface of the earth. f. Explain the effects of physical processes (plate tectonics, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents, and tides). h. Describe soil as consisting of weathered rocks and decomposed organic material WeatheringMountains wear down over time. Due to the Suns energy, wind, and water, mountains begin to crumble as soon as they are formed.

http://safari.glynn.k12.ga.us/?a=6856&d=02323AAWeatheringThe Smokey Mountains are much older than the Rocky Mountains.

WeatheringAt one time, the Smokies were as tall as the Rockies and also had sharp peaks.

WeatheringWeatheringWeathering is simply the chemical and/or physical breakdown of a rock material--weathering involves specific processes acting on rock materials at or near the surface of the Earth

WeatheringIn other rocks, minerals may slowly dissolve.Eventually the surface of ALL rocks crumbles, or weathers.

Types of WeatheringMechanical Weathering(physical)Takes place when rock is split or broken into smaller pieces of the same material without changing its composition.Example: Breaking of a rock cliff into boulders and pebbles

WeatheringMechanicalCommon weathering processes:Frost action

Wetting and drying/Wind

Action of plants and animals

Loss of overlying rock and soil

Rate of WeatheringThe type of rock and climate determine how fast a rock will weather.Types of WeatheringChemical (decomposition) takes place when the rocks minerals are changed into different substances.Water and water vapor are important agents of chemical weathering.Example: Formation of clay minerals from feldspar

Types of WeatheringThe two processes of weathering, mechanical and chemical seldom occur alone!Since water vapor is present in the air everywhere means that chemical weathering occurs everywhere.

Changing conditions of wetness and dryness cause rocks and minerals to break down.Weathering occurs quickly when running water knocks rocks against each other.Types of Mechanical WeatheringFrost action or Ice Wedging: Water takes up about 10% more space when it freezes.This expansion puts great pressure on the walls of a container. Water held in the cracks of rocks wedges the rock apart when it freezes.Often occurs in places where temperatures vary from below the freezing point of water to above the freezing point.Types of Mechanical WeatheringFrost action or Ice Wedging contOccurs mostly in porous rocks and rocks with cracks in themBare mountaintops are especially subject to ice wedging.

Types of Mechanical WeatheringRepeated wetted and dryingEspecially effective at breaking up rocks that contain clay.Clays swell up when wet and shrink when dry.Causes rocks that contain clay, such as shale, to fall apart.

Changing conditions of wetness and dryness cause rocks and minerals to break down.Weathering occurs quickly when running water knocks rocks against each other.Types of Mechanical WeatheringAction of plants and animals:Lichens and mosses grow on rocksThey wedge their tiny roots into spores and crevices.When the roots grow, the rock splits.

Plants cause weathering when their roots grow into small cracks in a rock.Animals cause weathering when they dig into soil or burrow underground.

Types of Mechanical Weathering

Types of Mechanical WeatheringAction of plants and animals:Larger trees and shrubs may grow in the cracks of boulders.Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil.These holes allow air and water to reach the bedrock and weather it.

Types of Mechanical WeatheringExfoliation

Loss of Overlying Rock and Soil

Sheet jointing on a granite outcrop produces cracks in the rock, thereby exposing more of the rock surface to weathering.

Exfoliation is a weathering process that results in rock layers peeling away as they expand or contract.

Types of Chemical WeatheringChemical weathering is the chemical breakdown of rocks. Results mainly from the action of rainwater, oxygen, carbon dioxide, and acids of plant decay.

Moss and lichens on rocks will eventually cause them to break down because of chemicals they release.Agents of Chemical WeatheringOxidationThe chemical reaction of oxygen with other substances is called oxidation.Oxidation is when the element iron combines with oxygen and water to make rust.

Agents of Chemical WeatheringAcid PrecipitationCarbon dioxide dissolves easily in water.It forms a weak acid called carbonic acidThis is the same compound that is in carbonated drinks.Attacks many common minerals such as feldspar, hornblende, augite and biotite mica.The original mineral is changed into a clay mineral.Agents of Chemical WeatheringHollows out great caverns in limestone bedrock.

Agents of Chemical WeatheringAcids are formed from the decay of plants and animals.These acids are dissolved by rainwater and carried through the ground to the bedrock.Agents of Chemical WeatheringCarbon dioxide and sulfur compounds released by industries unite with water in the atmosphere to form acid rain.Increasing amounts of acid rain in the environment increase the rate of chemical weathering.Factors that affect weatheringWeathering is slowest in dry, cold climates.Running water speeds up mechanical weathering and chemical weathering.The kind of minerals found in a rock also affects how fast it weathers.The greater the surface area of a rock or mineral compared to its volume, the faster it will weather.

Weathering

The process of breaking down rock.Mechanical Weatheringexfoliationwindrunning waterrock fallfrost wedgingChemical Weatheringroot wedgingrustchanges in rock mineralsActivity:

Imagine that you are a tin can-shiny, new, and clean. But something happens, and you dont make it to a recycling bin. Instead, you are left outside at the mercy of the elements. In light of what you have learned about physical and chemical weathering, write a story about what happens to you over a long period of time. What is your ultimate fate?

Do Now:ErosionEQ- How do rocks and minerals break down?Define chemical weathering and describe its causes.Chemical weathering occurs when chemical reactions dissolve the minerals in rocks or change them into different minerals. This type of weathering changes the chemical composition of the rock, which can weaken the rock. EQ- How do rocks and minerals break down?GPS: S6E5. Students will investigate the scientific view of how the earths surface is formed d. Describe processes that change rocks and the surface of the earth. f. Explain the effects of physical processes (plate tectonics, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents, and tides). h. Describe soil as consisting of weathered rocks and decomposed organic material ErosionErosion is the process of moving pieces of rock and sediment by wind, water, ice, or gravity.

Erosion Moving SedimentWeathering breaks rock into bits and pieces called sediment.

How does sediment get from a mountain peak to a beach?ErosionWeathering breaks rock into bits and pieces called sediment.Wind erodes mountains and moves sediment, but not as well as flowing water.

ErosionRunning water, wind and ice are all involved in moving sediment. Sediment generally moves downhill because of the force of gravity.

Running water- like that found in rivers, streams, and waterfalls carries sediment.- a river is a large, flowing body of water-a stream is a small river.-a channel is the path that a river or stream followsErosion Running water moves sedimentThe process of depositing sediment after it has beenmoved by water, wind, or ice is called deposition.

The amount of sediment carried and deposited by water depends on many factors:

the volume of water, the slope of the land, how rocky or smooth the land is.ErosionVolume:

The volume of running water affects how much sediment can be carried. When the volume of flowing rainwater is small, some sediment is moved. After a heavy rainfall, the greater volume of water can move a lot of soil or sediment from yards. Slope:

Slope refers to how steep the land is, another word for slope is gradient. The steeper the slope, the faster the water and sediment will move over land. Faster water means that larger particles can be moved and more particles can be moved at one time. Rocky vs. Smooth:

Rocky landscapes can trap sediment causing the sediment not to travel far. A smooth landscape or river bed might mean that sediment can be carried a longway.

ErosionA stream table can model how water flows over the land.The steeper the slope, the faster the water and sediment will move over land.

Erosion Sorting sediment:How fast water moves is directly related to how much energy it has.Both the speed of water and its energy are directly related to how big a piece of rock can be moved. Fast, high energy water can move big pieces of rock.Slow-moving water can only move fine sediment. You can tell the speed of flowing water by the size of the rock pieces found on a stream bottom.The grains settle in order, making a pattern called graded bedding.

Erosion

ErosionInterpreting layers of sediment:Sedimentary rocks hold clues to their past.If you know the up direction, you know the direction of younging this is the directions of younger layers.

Erosion

Cross bedding, is easy to recognize in sedimentary rocks where one layer ends and another layer passed over it.When sediment is carried by the wind or running water, it often forms a patternof alternating beds where it is deposited, this pattern is cross bedding. ErosionMoving sediment by ice:Particles that are trapped in ice or suspended in water can cause weathering.As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice.

Erosion

As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice.

Glaciers are formed from accumulation of snow over hundreds or thousands of years.As snow piles up and pressure increases, it changes into ice.

The fine rock powder that results from glaciers is called rock flour.

Rock flour can be washed into lakes and make them a milky blue color.

Types of glaciersAlpine Glaciers (Valley Glaciers) - small to medium glaciers formed in mountains where the temperature is low enough to prevent snow from melting during the summer. - Flow slowly down mountain slopes and valleys eroding as they go.

U-shaped ValleysAlpine glaciers typically follow a river bed and cut the deep V into a smoother but larger U-shape as they move down the mountain. The sides of the U-shaped valleys are much steeper and rugged than when they were shaped by a river. The ice in a glacier is much more destructive to the land than the running water in rivers.

Continental GlaciersHuge continuous masses of ice that form from layers of snow that compact and freeze into ice.

How do Glaciers move?

Glaciers move by two different methods:

when ice at the bottom of the glacier melts due to the weight of the glacier the glaciers begins to slide on the melted water.

when ice crystals within the glacier slip over each otherGlacial ErosionAs glaciers move they break off pieces of rock and sediment, pick them up and carry them with them. As the glacier begins to melt the sediment is deposited on land.

More on moving sedimentWind can move particles of sediment from one place to another.Beach dunes hold large amounts of wind deposited sand. Loess is another wind-blown deposit of fine sediment.

Mass wasting is the downhill movement of large amounts of rock and sediment due to the force of gravity. More on moving sediment