Weathering: when rocks and soil are worn down.
Erosion: when the material that is worn down is carried away by wind, water, living beings or gravity.
Deposition: the dropping, or releasing of sediments that have been moved from one and build up in another.
Constructive Forces
Deposition: Deltas and Sand dunes
Sand dunes:
mounds or ridges of sand that the wind forms along coastlines. They may form in long, irregular rows set back from the water.
Deltas:
land forms formed at the mouth of a river where the river flows into the ocean, estuary, lake, or reservoir. Deltas are formed from the deposition of the sediment carried away by the river and dropped as it leaves the mouth of the river.
Earthquakes:
Earthquakes can be both a constructive and destructive force. When the fault lines move they can cause incredible damage (destructive) and they also can cause new land formations (constructive). Almost always though, they are destructive!
Learn More:
Faults:
Earthquake faults are caused by the Earth’s crust moving upward, downward, and sideways. Normal faults occur when plates move apart. Reverse faults develop when plates smash together. The San Andreas Fault is a place where plates slip past each other.
Learn More:
Volcanoes:
Volcanoes can be both a constructive and destructive force.
Learn More:
Destructive Forces
Weathering:
Weathering is the breaking down of rock.
Mechanical (Physical)
Mechanical weathering refers to the physical separation break-up of a material.
When wind blows against a solid surface, it’s pushing against it. The push is small, of course. But, over time, all the pushing adds up. It might chip pieces off of the solid. If they end up blowing far away, we call it wind erosion.
Ocean waves smash into the coast.
Coastlines often have very unique shapes to them. That’s because waves weather them over time. Each new wave digs into the rock a little. Much later, the digging can produce interesting patterns.
Small waves break against coastal rock.
Chemical:
The next type of weathering we’re going to look at is a little different. We can’t usually watch it happen. It takes place at the atomic level. But, we can learn from examples of what we know as chemical weathering.
Hydrolysis
Hydrolysis is when water, chemically known as Hâ‚‚O, reacts with a rock to form a new material. This can happen when rainwater hits the igneous rock granite. Some of the minerals in granite react with water to form clay. This is an example of weathering because the new clay is much easier to erode.
Leaching
Leaching is a simple, but important force. It’s when rainwater, which is naturally acidic, dissolves rocks. This happens a lot with limestone (a type of sedimentary rock). If runoff moves through a deposit of limestone, it might create a cave.
A cave. Caves are created by chemical weathering.
Biological :
Our last type is actually quite simple. It’s when a living thing does any sort of weathering. It usually refers to soil: Animals dig through it, and plants grow in it.
Meerkats weather the soil by digging holes through it.
This biological weathering is great for the environment! Organisms evolve to survive in their biomes, not destroy them. Their actions are only inconvenient for us.
Erosion:
Erosion is simply the process by which the earth’s surface gets worn down. This usually happens as a result of water (rain, rivers or oceans) and wind. Erosion is the 2nd part of a cycle. First the earth is worn down through weathering. Then the weathered material erodes as a result of water and wind. Finally, the material that has eroded stops somewhere else in what is known as deposition.
Learn More:
- Wind Erosion
- Beach Erosion
- Interactive Erosion Activity
- Investigate Erosion on Your Own
- The Grand Canyon is an Example of Erosion
- Glaciers Cause Erosion
- Critters & People Cause Erosion
- What’s the Difference between Weathering and Erosion?
- How Erosion Affects Farmers
- See some Different Landscapes Created by Erosion
- Brain Pop Erosion
Impact of Organisms:
One of the main causes of erosion are all the billions of critters that continuously dig up the soil in search of food and homes. Insects, worms, reptiles, and mammals all help to disturb the upper layers of the Earth. Once soil is disturbed, then wind and rain can more easily wash it away. While it’s easy to point our fingers at the other members of the animal kingdom, it’s important to remember that the biggest culprit when it comes to biological erosion is humans. The amount of erosion resulting from one storm hitting an open construction site or a freshly plowed field is often greater than all the erosion caused in the same area by other animals working more than 100 years!
The Dust Bowl of the 1930s was caused by a combination of soil erosion, drought, and high winds. These problems combined to cause great amounts of dust to be blown over many states and killed crops, animals, and people in the process.
Earthquakes:
Earthquakes can be both a constructive and destructive force. When the fault lines move they can cause incredible damage (destructive) and they also can cause new land formations (constructive). Almost always though, they are destructive!
Learn More:
Volcanoes:
Volcanoes can be both a constructive and destructive force.
Learn More:
c. Ask questions to obtain information on how technology is used to limit and/or predict the impact of constructive and destructive processes. (Clarification statement: Examples could include seismological studies, flood forecasting (GIS maps), engineering/construction methods and materials, and infrared/satellite imagery.)
Seismological Studies:
Seismographs – Seismographs are used to record and predict earthquakes.
Richter Scale:
Scientists use the information provided by a seismograph to determine the severity of an earthquake. The Richter Scale scores earthquakes from 1 to 10 depending on the amount of movement that the earthquake causes. Every whole number on the scale represents the earthquake being ten times bigger. For example, a 5.0 on the Richter Scale is ten times bigger than an earthquake measuring 4.0. Scientists have recently begun using a newer, more specific scale to measure earthquakes called the Moment Magnitude Scale (MMS).
Flood Forecasting:
Using GIS Maps
Dams
Dams help control the flow of water down major rivers. That flow of water is then turned into electricity. The Tennessee Valley Authority, which was created as part of FDR’s New Deal, built many dams in the Southeastern U.S. They still are a major source of hydro-electric power today. You can explore their site to learn more about dams, hydro-electricity and flood prevention
Levees
Levees are designed to control the flow of water. Unlike dams, they do not block a river. Instead they make the sides of the river taller to prevent flood damage to nearby cities, houses and businesses.
Storm Drain Management
Heavy rainfall can also lead to large amounts of water running through the city’s storm drain system. As more and more people live in cities, pollution becomes a bigger and bigger problem.
WoPoLi 