Destructive and Constructive Forces

Erosion and Deposition

Reshaping Earths surface-Human Impact

Have you ever seen a construction site? If so, then you have probably watched backhoes, bulldozers, and dump trucks moving dirt and other materials for the project. You might have seen the backhoes digging deep holes into the ground or the bulldozers smoothing the land to make a flat surface. Dump trucks might have been removing soil from the construction site. These changes that people make are small examples of what happens naturally to Earth’s surface.

Constructive Forces

 Constructive processes BUILD UP or ADD to features on Earth’s surface.

For example, lava erupting from a volcano cools, hardens, and forms new land on the area where the lava falls. This lava is ADDED to the land. it can fill in holes and even out land

Multiple Choice

constructive forces ____ land

• add to

• take away

Destructive Forces

Destructive processes TEAR DOWN or take away features on Earth’s surface. The winds and rains from a strong hurricane can wash part of a shoreline into the sea. Wind can pick up material and remove them from one area and then add them to a different place

Multiple Choice

Destructive forces ____ land

• add to

• take away

A continuous change

Imagine standing on the top of a mountain. When you look down, you might see a valley, a winding river, or the ocean. Now try to imagine what this same area might have looked like thousands of years ago. What might this same area look like thousands of years from now?

Open Ended

How might an area be different in 1,000 years?(atleast 3 sentences)

Weathering

One type of destructive process that changes Earth’s surface is weathering. Weathering is any chemical or physical process that breaks down rocks.

Chemical weathering changes the composition, or chemical makeup, of rocks.

Physical weathering changes the sizes of rocks by breaking them into pieces

Multiple Choice

Which type of weathering will break rocks into smaller pieces

• chemical

• mechanical

Weathering Agents

Water, wind, plants, and ice are agents, or causes, of both chemical and physical weathering.

Water, for example, can dissolve minerals in rocks.

Wind can grind and polish rocks by blowing particles against them.

Ice or plant roots can enlarge cracks in rocks and break rocks apart

Multiple Choice

Which weathering agent can grind and polish rock by blowing particles against them?

• water

• wind

• ice

• plants

Multiple Choice

Which weathering agent can grow into cracks and push rock to break

• water

• wind

• plants

Different rates of weathering

Because Rocks have different mineral compositions....rocks weather at different rates.

That means...because rocks are made up of different things(making them harder or softer than another rock) they will break down at different speeds.

Multiple Choice

A soft rock will weather ____ than a hard rock

• faster

• slower

• the same

What is Erosion??

What happens to material that is weathered? Much of it is TRANSPORTED to another place. Erosion is the removal of weathered material from one location to another . Erosion involves both the wearing away of landforms and the transportation of sediment.

Agents of Erosion

Agents of erosion are the things that will pick up the weathered material and transport it to another location.

Agents of erosion include water, wind, glaciers, and gravity.

All of these things will pick up the weathered sediment and move it to other places!

Fill in the Blanks

The four agents or erosion are water, wind,

, and glaciers

The rate(or speed) of Erosion

Like weathering, erosion takes place at different rates or speeds.

For example, a rushing/strong stream can erode a large quantity of material very quickly. However, a gentle or slow stream might erode a small amount of material very slowly.

Multiple Choice

Which will erode a rock faster

• a fast stream

• a slow stream

Four factors that affect rate of erosion

The major factors that affect the rate of erosion include weather, climate, the shape of the land(also called topography), and the type of rock.

For example, weathered rock is more easily eroded by heavy rain than by a gentle shower.

Strong wind transports weathered rock more easily than a gentle breeze does. Weathered rock moves faster down a steep hill than across a flat area. 

Deposition

You have just read about weathering and erosion, two processes that shape Earth’s surface.

Weathering breaks rocks into smaller pieces.

Erosion moves weathered material from one place to another.

After material has been eroded, a constructive process takes place. Deposition is the laying down or settling of that eroded material. Just like you go to the bank to drop off or deposit money, deposition is the dropping off of sediment somewhere else!

Fill in the Blanks

Of the three processes, which one happens first?

Multiple Choice

Which of the three processes moves the sediment from one place to another?

• weathering

• erosion

• deposition

Multiple Choice

Which of the three processes will lay down or drop off the sediment that has been carried into a new location?

• erosion

• deposition

• weathering