6th Grade Science-Chapter 4 Notes

Chapter 4, Lesson 1 Notes

*Moving water is the major agent of the erosion that has shaped Earth’s land surface.

*As water moves over the land, it carries pesticides with it.  This moving water is called runoff.

*The amount of runoff in an area depends on five main factors: the amount of rain an area gets, the area’s vegetation, the type of soil, the shape of the land, and how people use the land.

*As runoff travels downhill under gravity, it forms tiny grooves in the soil called rills.  When many rills flow into one another, they grow large, forming a gully.

*A gully is a large groove, or channel in the soil that carried runoff after a rainstorm.  Gullies join together to form a larger channel called a stream.

*A stream is a channel along which water is continually flowing down a slope.  A large stream is often called a river.  A tributary is a stream or river that flows into a larger river.

*Through erosion, a river creates valleys waterfalls, flood plains, meanders, and oxbow lakes.  The flat, wide area of land along a river is a flood plain.  A meander is a loop like bend in the course of a river.  An oxbow lake is a meander that has been cut off from the river.

*Deposition creates landforms such as alluvial fans and deltas.  Sediment deposited where a river flows into an ocean or lake builds up a landform called a delta.

*An alluvial fan is a wide, sloping deposit of sediment formed where a stream leaves a mountain range.  It is shaped like a fan.

*Groundwater is the term geologists use for underground water.  Groundwater can cause erosion through a process of chemical weathering.

*A deposit that hangs like an icicle from the roof of a cave is known as a stalactite.  Slow dripping builds up a cone-shaped stalagmite from the cave floor.

*Karst topography is a type of landscape in rainy regions where there is limestone near the surface and characterized by caverns, sinkholes, and deep valleys.

Chapter 4, Lesson 2 Notes

*Geologists define a glacier as any large mass of ice that moves slowly over land.  There are two kinds of glaciers-continental glaciers and valley glaciers.

*A continental glacier is a glacier that covers much of a continent or large island.  Continental glaciers can flow in all directions as they move.  Many times in the past, continental glaciers have covered large parts of Earth’s surface.  These times are known as ice ages.

*A valley glacier is a long, narrow glacier that forms when snow and ice build up in a high mountain valley.  The sides of the mountains keep these glaciers from spreading out in all directions.  Instead, they usually move down valleys that have already been cut by rivers.

*Glaciers can form only in an area where more snow falls than melts.  Gravity constantly pulls a glacier downhill.

*The movement of a glacier changes the land beneath it.  The two processes by which glaciers erode the land are plucking and abrasion.  As a glacier flows over land, it picks up rocks in a process called plucking.  Many rocks remain on the bottom of the glacier, and the glacier drags them across the land.  This process, called abrasion, gouges and scratches the bedrock.

*When a glacier melts, it deposits the sediment it eroded from the land, creating landforms.  The mixture of sediments that a glacier deposits directly on the surface is called till.  Till is made up of clay, silt, sand, gravel, and boulders.  The till deposited at the edges of a glacier forms a ridge called a moraine.

*A terminal moraine is the ridge of till at the farthest point reached by a glacier. 

*A kettle is a small depression that forms when a chunk of ice is left in glacial till and later melts.  If the kettle gets filled with water, a kettle lake forms.  Other features of glacial erosion or deposition include horns, arêtes, cirques, U-shaped valleys, and drumlins.

Chapter 4, Lesson 3 Notes

*Waves contain energy and are formed by winds.  Waves shape the coast through erosion by breaking down rock and moving sand and other sediment.

*One way waves erode is by impact.  Waves also erode by abrasion.  Waves coming to shore gradually change direction.  The change occurs as different parts of a wave begin to drag on the bottom.  The energy of these waves is concentrated on headlands.

*A headland is part of the shore that sticks out into the ocean.  It is made of harder rock that resists erosion by waves.  But over time, waves erode the headlands and even-out the shoreline.

*Ocean waves that hit a steep, rocky coast erode the base of the land there.  Where the rock is softer, the waves erode the land faster.  Over time the waves may erode a hollow area in the rock called a sea cave.  Eventually, waves may erode the base of a cliff so much that the rock above collapses.  The result is a wave-cut cliff.

*A sea arch is another feature of wave erosion that forms when waves erode a layer of soft rock that underlies a layer of harder rock.  If an arch collapses, a pillar of rock called a sea stack may remain.

*Waves shape a coast when they deposit sediment, forming coastal features such as beaches, sandbars, barrier beaches, and spits.

*A beach is an area of wave-washed sediment along a coast.  The sediment deposited on beaches is usually sand.  Most sand comes from rivers that carry eroded particles of rock to the ocean.

*As waves repeatedly hit the beach at an angle, some of the beach sediment moves down the beach with the current, in a process called longshore drift.

*One result of longshore drift is a spit, a beach that projects like a finger out into the water.  Incoming waves carrying sand may build up sandbars, long ridges of sand parallel to the shore.  A barrier beach is similar to a sandbar, but forms when storm waves pile sand up above sea level forming a long, narrow island parallel to the coast.

Chapter 4, Lesson 4 Notes

*Wind can be a powerful force in shaping the land in areas where there are few plants to hold the soil in place.  Wind causes erosion mainly by deflation.

*Geologists define deflation as the process by which wind removes surface materials.   When wind blows over the land, it picks up the smallest particles of sediment, such as clay and silt.  The stronger the wind, the larger the particles that it can pick up.

*Slightly heavier particles, such as sand, might skip or bounce for a short distance.  But sand soon falls back to the ground.  Strong winds can roll heavier sediment particles over the ground.

*In deserts, deflation can sometimes create an area of rock fragments called desert pavement.  There, wind has blown away the smaller sediment, leaving behind rocky material.

*Abrasion by wind-carried sand can polish rock, but it causes relatively little erosion.  Geologists think that most desert landforms are the result of weathering and water erosion.

*Wind deposition happens when the wind slows down or meets an obstacle, such as a boulder or clump of grass that traps the windblown sediment.  Wind erosion and deposition may form sand dunes and loess deposits.

*When the wind meets an obstacle, the result is usually a deposit of windblown sand called a sand dune.  Sand dunes occur on beaches and in deserts where wind-blown sediment has built up.  Sand dunes come in many shapes and sizes.  Sometimes plants begin growing on a dune.  Plant roots can help to anchor the dune in one place.

*Sediment that is smaller than sand, such as particles of clay and silt, is dropped far from its source in large deposits.  This fine, wind-deposited sediment is loess.  Loess helps to form fertile soil.  Many areas with thick loess deposits are valuable farmlands.

Chapter 4, Lesson 5 Notes

*Every place in the state of Florida is 100 kilometers or closer to salt water.  About 25 million years ago, Florida was under water, and many of the state’s landforms are a result of the changing sea level.

*The Florida peninsula sits on a huge limestone platform.  Limestone is a sedimentary rock formed from the remains of tiny sea animals.  When the animals died, their shells and skeletons sank to the bottom of the ocean and accumulated into layers.  Over millions of years, these layers hardened into rock.  The size and shape of Florida changed repeatedly as sea levels rose and fell.

*Scientists have identified distinct regions in Florida where different landforms are found.  The three main regions are the northern highlands, the central highlands, and the coastal lowlands.

*The northern highlands consist of gently sloping plateaus, while the central highlands are made up of long ridges.  The surrounding coastal lowlands include dunes and beaches on the Atlantic and Gulf coasts, as well as vast wetlands at the southern end of the peninsula.

*Over millions of years, erosion and deposition have shaped Florida’s landscape.  Different types of landforms in Florida include rivers, hills and ridges, coastal features, lakes, and wetlands.

*Florida’s streams and rivers carry and drop sediment along the coast, helping to form beaches, barrier islands, and deltas.  Long, raised strips of land called ridges run parallel to the coast.  Florida’s ridges mark ancient shorelines.  Waves and currents have shaped Florida’s long coastline, forming bays and building up sandbars and barrier islands.  Many southern Florida beaches consist of coral from offshore reefs.

*There are more than 7,000 lakes across Florida, most of which formed after erosion dissolved the limestone plateau beneath them.  The Everglades is a large wetland that covers several thousand square kilometers.  The Everglades formed on a flat block of limestone that tilts gently toward the south.