Building Up Earth’s Surface Unit C Chapter 6 Lesson 3 C24 – C29

Objectives Recognize that constructive forces build up Earth’s surface features. Recognize deposition to be the dropping of sediments by water, wind, or ice. Understand that gravity is always the final process in sedimentation.

Main Idea Forces such as deposition and volcanic activity build up Earth’s surface features.

Review In the last lesson we discussed how the earth wears down. The process of weathering and erosion. Erosion carries away sediment, but what happens to it then? When it is dropped or released in a new area this is called deposition.

Deposition Deposition is a constructive force. This means it builds up the land. When the sediment is dropped in a new location, you are adding to the existing land there. You are building it up.

River Systems Recall that the source of a river is usually inland at some high elevation. The water picks up sediment as it flows downward. At the mouth of the river the water empties into a lake or ocean. The mouth is level, causing the water to lose energy and drop the sediment.

Alluvial Fans Is a fan-shaped land mass that forms after a river rushes down a steep slope, then slows over a flat plain.

Delta A low plain that forms where a river enters an ocean. If the river is large, so is the delta. The Mississippi River has a large delta that extends out into the Gulf of Mexico.

Meanders As a river flows across a flat plain, its course begins to wind in curves called meanders. They increase in size as water erodes the outside of each curve and deposits sediment on the inside.

Flooding Flooding of rivers on lowlands deposits sediment. This sediment builds up the flood plain.

Why is sediment deposited as the slope of a river bed levels out? Because the sediment slows down and settles out.

How are Earth’s surface features built up? Through forces such as deposition and volcanic activity.

What is the difference between an alluvial fan and a delta? Both form when the flow of river water decreases quickly. An alluvial fan forms where a river flows down a steep slope onto a flat plain. A delta is a low plain, and forms where a river enters an ocean.

Pushing up Earth’s Surface Surface features can be pushed up from below. Below earth’s surface the temperature is so hot it melts rock. Melted rock below the Earth’s surface is called MAGMA

Magma Originates in a layer just below the crust. Pressure causes magma to push up Earth’s crust creating round, dome-shaped mountains. Mount Olympus

Magma surfaces Magma can work its way through the crust. When it flows onto Earth’s surface it is called LAVA. As lava flows, it cools and hardens into rock. Kilauea, Hawaii

Shield Cones Lava that has built up to form a huge deposit with gentle sloping sides. Often form on the ocean floor. The Hawaiian Islands are the tops of shield cones.

Hot Spots The Hawaiian Islands were formed due to a hot spot. As the Earth’s crust moves over the hot spot, new shield cones are formed.

Building Mountains The Himalaya Mountains in Central Asia were formed from a different constructive force than magma. As the Earth’s plates moved, they moved into each other. The pressure caused the crust to fold upward.

Himalaya Mountains

Remains The remains of living things can build up Earth’s surface. The chalk cliffs of Dover, England are made of shells of tiny sea animals. The shells eventually raise to the surface.

Coral Reefs Another type of formation produced from the remains of living things. In shallow tropical waters, tiny animals called corals gather in colonies. As they die, their skeletons build up into a bumpy ridge called a reef.

What process created the Himalayas? They formed when huge sections of Earth’s crust pushed into each other.

How are chalk cliffs and coral reefs alike? How are they different? Both are formed from remains of living things. Chalk cliffs are made of the shells of tiny sea animals that were deposited on the sea floor millions of years ago, then raised to the surface. Coral reefs are the skeletons of tiny animals called corals that build up in tropical waters

Glacial Deposits As we learned in Social Studies thousands of years ago there were large glaciers over Asia, Europe, and North America. The ice chunks were forces of erosion. Huge amounts of soil & rock were pushed ahead of the ice and carried along in the glacier’s bottom layers.

Glaciers The ice melts It had changed the landscape. Rock material deposited by a glacier is called till. Till is dragged along the icy base.

Glacier Moraines Moraines are deposits of till at the front or snout of a glacier. Long Island, NY is the terminal moraine left when the last ice sheet melted. Exit Glacier in Kenai Fjords National Park near Seward, Alaska 

Eskers Steams flowing through tunnels in melting glaciers deposit sand & gravel in ridges. These winding ridges are called eskers.

REVIEW

Small islands can form during the constructive process called? deposition

Landforms are found on the ______, which is Earth’s outer rocky layer. crust

The End