Grade 6 Science Enrichment

 Landforms are the physical features on the Earth’s surface such as, valleys, rivers, mountains, and plateaus.  Forces such as flowing water, waves, wind, ice, and movements (volcanoes) inside the Earth are constantly changing landforms.

 Destructive forces, such as weathering and erosion, wear down the Earth's surface features.  Constructive forces, such as deposition and volcanic activity, build up the Earth's surface features.

 Weathering is the process of breaking rock into small pieces such as, sand, silt, clay and other tiny pieces called sediment.  Sediment are the very small pieces that come from the weathering of rock.  Water, wind, ice, and mass movement are all causes of weathering.

 There are two types of weathering.  Physical weathering – when rock physically breaks apart. This can be caused by: plant (root wedging), ice (shatters the rock because of expansion), water (freezes then shatters the rock because of expansion).

 Chemical Weathering – when substances in the rock go through chemical changes that weaken the rock and cause it to break (think of your bicycle rusting): acid rain, pollution, lichens, and mosses all cause chemical weathering. This is caused by acid rain. rain.

 Water will weather rock in several ways. 1. Fast flowing water can carve deep canyons in rock. A canyon is a deep valley with steep sides. It often has water running through it. Flowing water can also have rocks tumble against each other, breaking them into smaller pieces. 2. Ocean waves can weather cliffs and cause them to fall into the sea. 3. Rain will seep into to small cracks in rocks. If the water freezes, it will expand, breaking the rock apart. 4. Acidic rain (rain with pollution in it) can also dissolve rock.

 After weathering has broken rock into sediment, erosion will move the sediment from one place to another.  Erosion is the process of moving sediment from one place to another.  Water, wind, and ice are also causes of erosion. They are able to change the Earth’s landforms by moving rock and soil. 1. Water  At the shore line, water will erode (carry away) sediment from weathered cliffs.

 Rainfall will carry (erode) sediment into rivers and streams. Rivers will carry the sediment and move it downstream.

2. Wind  Wind will carry away the pieces loosened by weathering. The wind moves the sediment from place to place. 1. Wind can blow sand and small pieces of rock from one place to another. 2. Ice  Ice can erode everything under it when it is in the form of a glacier. A glacier is a huge and thick sheet of ice that moves slowly.

 Deposition is the process of leaving, or depositing, sediment in a new place.  Most rivers deposit (leave) sediment in flat areas along their river banks. These areas are called flood plains.  Rivers also deposit (leave) sediment in an area called a delta. A delta is a broad area at the mouth of a river. This is a picture of the delta of the Mississippi River.

 Wind can blow sand into large mounds called dunes. Dunes is a hill of wind-blown sand.

 Mass movement is the downhill movement of rock and soil because of gravity.  Examples of mass movement are: A. Mudslide: moves wet soil. Heavy rains off the California coast created mudslides moving down a canyon. This mudslide happened because the soil was full of water. B. Landslide: moves dry soil and rock. Landslides happen when the gravity is stronger than what is holding

 Sinkhole – a sinkhole is different from other types of mass movement. A sinkhole is a large hole in the ground that opens suddenly.  They form when rock under the surface breaks up or becomes weak.

 Erosion and deposition can change landforms or produce new ones.  Rivers can deposit (drop off, leave) sediment that build deltas.  Delta is a broad area at the mouth of a river where sediment has been deposited.  Glaciers also form new landforms. They push mound of rock and soil in front of them. When a glacier melts, they leave long ridges of rock and soil.

 Long Island and Cape Cod are made up of these glacier mounds.  Volcanoes that erupt can from new islands.  Volcanoes underwater also erupt. They keep building rock until they appear above the sea surface as islands. The Hawaiian Islands were formed this way.