Questions to Ask: Changing Earth
Erosion and Weathering
What is a constructive force?
A constructive force is one that builds something up. For example, a mountain forming as a volcano erupts or a delta forming as deposition occurs.
What is a destructive force?
A destructive force is one that breaks something down. For example, erosion carries away rich top soil from farmland during flooding.
How do constructive and destructive forces work together to change the Earth’s Surface?
Often a force that is destructive for one area is constructive for another.
Erosion(destructive) carries away soil from farmland but later deposition (constructive) occurs and a delta of rich soil forms at the mouth of a river.
The plates shifting along a fault may cause an earthquake that causes destruction of some parts of land but can also form new mountains as the plates continue to move.
What is weathering?
Weathering is the decomposition of Earth rocks, soil, and minerals through direct contact with the planet's atmosphere.
What things in nature cause weathering?
Earthquakes, wind, water, ice, chemicals, rain, plant growth, animal activity
What are the two main types of weathering?
Mechanical (physical) and chemical
- What is mechanical weathering?
Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure.
What is chemical weathering?
Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces. Parts of the rock are changed into new substances as minerals dissolve or are oxidized. The dissolved minerals are then carried away by erosion, leaving behind rocks with holes. Oxidation can be seen in rocks with a high iron content in the form of rust.
How does abrasion weather rocks?
Abrasionis a type of physical weathering caused by rocks rubbing against each other. This occurs mostly in streams where fragments bounce off each other and round out. Wind can also carry small particles of rock that continually strike larger rock surfaces, carving some unusual natural shapes
How can freezing water cause weathering?
When water freezes, it has an unusual property – it expands (unlike most materials, which contract). When water turns to ice it expands and takes up more space. When water in tiny cracks in rocks freezes the cracks become larger. As this happens many times, the rocks eventually break apart.
How can plants and animals cause weathering?
Plants, such as lichens, mosses, and tiny roots, wedge their way into pores, crevices, and cracks. The seeds and roots grow and expand, causing cracking. Animals, such as earthworms and small burrowing mammals, act as transportation for particles that get broken down.
What kinds of materials weather most quickly? Most Slowly?
Generally the softer the rock the more quickly it will erode and the harder the rock the longer it will take.
What is erosion?
Erosion is the removal of weathered materials (sediment, soil, rock and other particles) in the natural environment. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals.
What is deposition?
Deposition is the settling of sediments to a resting place. Deposition occurs when a river, glacier, or sea is no longer able to carry its load for some reason, for example a shallowing of gradient, decreasing speed, decreasing energy, decrease in the volume of water in the channel, or an increase in the friction between water and channel.
How do weathering, erosion, and deposition work together to change the Earth’s surface.
Weathering breaks down Earth materials into smaller pieces that create new soil. Erosion then carries the weathered material away towards a new place. When the materials are deposited in a new place, a new landform results.
How was the Grand Canyon formed?
The Grand Canyon was formed by weathering and erosion by wind and water. The depth was carved by water. The width is due to weathering and erosion by both wind and water. The canyon is still forming today, as these processes continue.
How can erosion be both constructive and destructive?
Erosion is destructive when it carries away rich topsoil from farmland. It is constructive because it moves the material to a new place that will benefit from the soil once it is deposited.
How can glaciers cause erosion?
Glaciers erode in two different ways, plucking and abrasion. Plucking happens when materials are broken from the bedrock and plucked from the place that it has been for centuries. These materials are forced to move with the glacier and cause deep scratches and large holes to be carved from the bedrock. This is called abrasion. During abrasion smaller particles act like a large piece of sand paper and cause smaller grooves to be carved into the land. This process also polishes rock surfaces that were exposed during the plucking process or that were already exposed before the glacier reached them.
Clues to the Past
What is a sedimentary rock?
Little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock-called sedimentary rocks.
What is sedimentation?
Sedimentation is a general term for the processes of erosion, transport, and deposition. Sediments are loose Earth materials such as sand that accumulate on the land surface, in river and lake beds, and on the ocean floor. Sediments form by weathering of rock. They then erode from the site of weathering and are transported by wind, water, and ice, all operating under the influence of gravity. Eventually sediment settles out and accumulates after transport; this process is known as deposition.
What happens to sediments carried by a river as the water slows?
As the river slows it does not move with enough force to keep carrying all the sediments. Deposition occurs, creating a new landform such as a delta or new sedimentary layers that may later become sedimentary rocks.
A geologist says, “Rocks can talk!” What does that mean?
By examining the fossils found in the layers, scientists can tell a history of the Earth long ago. The order of the layers tells what happened over time. They can tell scientists whether the area was a land or an aquatic environment. The type of fossil can also yield a relative age of the rock.
What is superposition?
The oldest layer is on the bottom and the newest layer is on the top of the Earth’s surface. Layers are usually found in the order in which they formed with the oldest being the deepest.
What is a fault?
A fault is a break in the rocks that make up the Earth’s crust, along which rocks on either side have moved past each other. Not every crack in the ground is a fault. What defines a fault is the movement of the rock on either side.
What do mountains have to do with cracks in the Earth’s crust?
Cracks in the Earth’s crust are called faults. The large chunks of the earth’s crust (called plates) can move along these faults. The movement can build mountains as the surface folds or slips.
Your friend says, “The ocean floor is flat.” What evidence can you site to persuade him he is mistaken?
Explain that there are several fault lines in the ocean floor, under the ocean water. Plates move here just as they do above water. This movement can cause mountains to build, deep trenches to form, and other landforms. Cite Hawaii as an example-it was formed as a result of repeated volcanic eruptions under the water, until the mountain built up enough to reach the surface of the water. This process continues today. We may have new islands and maybe even a new continent some day in the future.
What is a dune?
A dune is a hill of sand built by wind.
How does a sand dune form?
Wind blows sand around and it piles up.
What happens to a beach as waves continuously pound it?
Beaches are constantly moving, building up here and eroding there, in response to waves, winds, storms and relative sea level rise. As the waves pound the shore, sediments are carried away to offshore deeper areas or deposited in a new place.
Should humans interfere with the natural course of nature and attempt to prevent beach erosion? For example, building a levee or a damn to alter the flow of water?
There are two sides and this can be a good discussion question.
Good-prevent flooding, garner water flow power to create electricity.
Bad-can fail such as the levees did in New Orleans during Hurricane Katrina and cause massive flooding
What is a volcano and how does it form?
A volcano is a place on the Earth's surface where molten rock, gases, and dash erupt through the earth's crust. Volcanoes form when hot material from below rises and leaks into the crust. The heat causes the material to expand and it exerts pressure on the Earth’s surface. It often works its way through cracks to the surface or can erupt in an explosion if the pressure becomes too great. Repeated eruptions build a volcanic mountain.
What are some ways that mountains can form?
Faulting, folding, volcanic activity