Earth Science--Weathering, Erosion, and Deposition--8th Grade

Glacier

A glacier is a naturally formed mass of ice and snow that moves downhill on land under the influence of gravity. Mountain glaciers are found in high mountain valleys around the world. Ice-sheet, or continental, glaciers cover huge landmass regions.

Factor affecting the rate and type of Weathering #3

A rock's mineral composition affects the rate of weathering because different minerals have different physical and chemical properties. Some minerals, such as calcite in limestone and marble, weather rapidly because they dissolve in slightly acidic water. In contrast, the mineral quartz does not react chemically with most substances in the environment. Thus, quartz is largely unaffected by chemical weathering and is commonly found as sand in many environments.

Tributary

A smaller stream that flows into a larger stream is called a tributary.

Sediment features

A solid sediment in wind, beach, or stream erosion will become smooth, rounded, and smaller. The longer the time the sediment is eroded, the smaller, smoother, and rounder it becomes. Wind-blown sediments are often more frosted (pitted) than stream sediments. Glacial sediments are only partly rounded (sub-rounded), and often have scratches of various sizes and directions on them. Sediments produced by physical weathering or moved directly by gravity are often very angular in shape.

Characteristics of sediments (size)

All other factors being equal, the larger sediments settle out first when wind or running water slows down. This occurs because the larger sediment particles are heavier and therefore sink faster.

Characteristics of sediments (Density)

All other factors being the same, the higher the density of a sediment, the faster it will settle out of air or water. If two particles have the same size and shape, the denser one will be heavier.

Wind erosion

Another agent of erosion is wind. When loose sediments the size of sand or smaller are present, nearby solid surfaces are susceptible to erosion by wind. Arid regions, such as deserts, and lake or ocean coastlines are the most common places where loose sediments are available for wind erosion. There are two main aspects to wind erosion—deflation and sandblasting, or abrasion.

Form of Chemical Weathering #2

Another form of chemical weathering is the effect of water on minerals. Water is often called the universal solvent because, over time, water can dissolve most rock materials. Acids from decaying organic matter mix with groundwater and aid in dissolving rocks.

Form of Physical Weathering #2

Another type of physical weathering occurs when the confining pressure on rocks is decreased when rock is removed by humans in mining or quarrying or by natural processes such as in erosion or when glaciers melt. When the rock (including ice) is removed, the pressure is reduced on the remaining rocks and these rocks expand and crack.

Meanders

As the stream grows larger and gets to its later stages, it begins to shift its course in a series of bends or turns called meanders. In shifting from side to side, the stream carves a wider valley. Greater the slope, the less meanders.

Moraine

At the end of a glacier where there is a balance between melting and forward movement, the sediments it carries are just dropped in unsorted sheets or piles called a moraine.

Stream energy #1

At the source, or beginning, of the stream the system has a maximum of potential energy. As the stream flows toward its mouth, or end, potential energy is continuously being transformed into kinetic energy.

Delta #1

At the very end of a stream, there is often a fan-shaped delta. A delta forms from sediments deposited over time from the ever-shifting channel at the stream's mouth.

Longshore current

Because waves usually strike the shore at an angle, the waters near shore are often pushed in one direction along the shore. This causes a flow of water, sometimes called a longshore current, that can carry large amounts of sediments parallel to the shore.

Factor affecting the rate and type of Weathering #1

Both the rate and type of weathering are dependent on the exposure of rocks to air, water, and the actions of living things. Generally, the closer a rock is to Earth's surface, the faster it will weather. The difference in the amount of solar energy on the north and south sides of mountains affects the temperature and amount of moisture available for weathering. This often results in different soil characteristics on opposite sides of mountains.

Wave energy

Breaking waves continually pound against the shoreline, unleashing a great amount of energy. Usually, waves arrive at an angle to the shore. Arriving waves often become refracted or bent, concentrating energy on parts of the shore that extend out into the water. Over time, these parts of the shore erode away. If the coastline is straight, the wave energy is more evenly spread out, and the waves pound the entire shoreline.

Deflation

Deflation takes place in areas with small, loose sediments exposed to the atmosphere. Winds readily blow away the loose sediments, lowering the land surface. The lowering of the land surface can continue until there are no longer any small solid sediments exposed to the winds.

Deposition #2

Deposition usually occurs when the velocity, or speed, of the stream, wind, or other erosional system decreases or just stops moving. Two types of factors—the velocity of the erosional system and characteristics of the sediments themselves—affect the rate of deposition.

Streams carry sediments in different ways.

Dissolved minerals are carried in solution. Solid sediments of small size—including clay-sized sediments—are carried suspended in the water. Larger solid sediments are usually carried by rolling, sliding, or bouncing along the stream bottom.

Flood plain #1

During times of flooding, the stream may flow out onto this wider valley and deposit sediments—forming a flood plain.

Driving force of erosion #2

Energy from the sun plays an important indirect role in erosion. The sun's energy drives the water cycle, producing precipitation that results in running water and glaciers. Insolation also "fuels" wind patterns that create ocean currents and waves.

Erosion Components

Erosion involves a transporting system with several components: an agent of erosion, such as a stream, glacier, wave, current, wind, or human activity. The sediments being moved and a driving force.

Characteristics of sediments (Saturation of dissolved minerals)

Evaporation, temperature changes, or increases in amount of dissolved minerals in a water body such as a lake, sea, or ocean may result in a saturated condition. When this happens, the dissolved mineral or minerals will settle or precipitate out of the dissolved condition and crystallize. As a result, rocks composed of one mineral, such as rock salt and dolostone, may form.

Form of Physical Weathering #1

Frost action breaks up rocks in a way similar to the formation of road potholes. When water freezes, its volume expands nearly ten percent. At temperatures below 0°C, water trapped in cracks freezes and expands, enlarging the cracks. After many cycles of freezing and thawing, the rock crumbles.

Sediment/velocity

Generally, the solid sediments being transported by a stream move much more slowly than the stream itself. The greater the velocity of a stream, the larger the sediment particles it can carry, and the greater the velocity, the more total sediments it can carry.

Plastic flow

Glacial movement often is by plastic flow. The glacial ice acts like a fluid, and many of its motions are like those of a stream.

Glacier movement #2

Glaciers move fastest in the middle and slowest at the sides. This is true because there is more friction at the sides of the valley than in the middle. In the cross-section, glaciers usually flow fastest near the top and slowest at the bottom because the greatest friction is at the bottom. At times, glacial motion is caused by sliding at the base of the glacier when liquid water helps to overcome friction.

Graded bedding formation

Graded bedding is most often associated with sediment-laden density currents. These currents are most common on the sloped ocean bottoms off the coasts of continents, and on lake bottoms where flooding streams rapidly decrease in velocity when they enter.

Stream velocity #1

Gradient (or slope of the stream) and discharge, (amount of volume of water in the stream) are factors affecting stream velocity. Generally, as either the slope or the discharge of a stream increases, the velocity increases.

Mass Movement #1

Gravity is the driving force behind erosion. It causes sediments to move downslope by way of running water, glaciers, and underwater currents. However, gravity can also act largely on its own by pulling rocks and sediments downhill in mass movements. Types of mass movements include: soil creep, debris flow, and debris fall.

Sorted sediments

If a deposit or layer of sediment has particles that are similar in size (or density, or shape), they are considered sorted sediments. The greater the similarity of size, the more sorted the sediments are said to be.

drumlin

If a glacier mounds up the ground moraine into a streamlined oval shape—something similar to the shape of the end of an inverted spoon—that feature is a drumlin. The drumlins indicate the direction a glacier came from by being oriented with direction of former glacial movement. Drumlins have steeper slopes pointing to the direction the glaciers came from.

Glacier movement #1

If more snow and ice accumulates than wastes away, the glacier will advance. If the opposite occurs, the glacier will retreat. It should be noted that ice within a glacier is always moving in a particular direction, even if the glacier retreats as its overall boundaries shrink.

Deposition and erosion energy changes #2

If one or more tributaries were to enter a stream, this would increase the mass or discharge of water, thus increasing the potential energy of the stream. The velocity of the stream would increase, causing erosion to increase and deposition of solid sediments to decrease.

Unsorted sediments

If sediments are very mixed in size (or density, or shape), they are considered unsorted sediments.

Terminal moraine

If the end or terminus of a glacier stays in one location for some time, the glacier builds up a pile of sediments called a terminal moraine.

Ground moraine

If the moraine is a thin sheet deposited from the bottom of the glacier, it is called a ground moraine. Ground moraines cover much of the northern 208 United States including much of New York State.

Cross bedding

If the winds change direction, beds of sand will cross one another at various angles producing a feature called cross bedding. Most sand in dunes is well sorted in sloping layers, and the sand grains are well rounded and have a frosted appearance due to numerous collisions of sand grains during erosion and weathering.

Barrier island

If this sandbar rises above average sea level, winds will help to pile up the sediments. Then vegetation can stabilize this offshore sediment pile, creating a barrier island.

Glacier deposits

In a solid erosional system such as a glacier, sediments of all sizes, shapes, and densities are deposited together when the glacier melts. This deposition results in the unsorted and unlayered characteristic of direct glacial deposits that cover much of New York State.

Early stages of the stream

In the early stages of the stream, most of its energy is used to downcut a narrow V-shaped valley. There usually is a steep slope and many abrupt changes in elevation resulting in waterfalls and rapids. Farther downstream, more water from tributaries and from ground water increases the size of the stream.

Erosion-deposition interface

Interfaces between erosion and deposition exist at the meanders in the model stream, and between the source and the mouth of the stream. They may also be found where changes in slope occur.

Stream abrasion

Larger solid sediments are usually carried by rolling, sliding, or bouncing along the stream bottom, resulting in rounding of sediments by stream abrasion. The way in which a particular type of solid sediment moves varies with how fast the stream flows.

Mass Movement #2

Mass movement—sometimes called direct gravity erosion—involves two major opposing forces. One force is the constant downward pull of gravity. The other force is friction, which attempts to keep objects in place. Rocks and other loose materials on Earth's surface slide downward when the forces holding them in place become weaker than the downward pull of gravity.

Ox-bow lake

Often the high velocity of a flooding stream will cut a straighter path through a meander. Depositions at the side of a stream will then separate the former meander from the mainstream—forming a curved lake.

Form of Chemical Weathering #1

One form of chemical weathering is oxidation—such as when iron combines with oxygen to make iron oxide, or rust.

Zig-Zag pattern

Over time, sediments on shore tend to move in a zig-zag pattern along the same direction as the longshore current. This movement occurs because breaking waves, bearing sediments, strike the beach at an angle. However, as water from the breaking waves washes back into the lake or ocean, it flows straight downhill.

V-shaped valley

Over time, streams carve deeper channels V-shaped valley start to form. The V-shape results from the combined actions of stream downcutting, runoff, and mass movement, which causes the sides of the valley to "cave in."

Soil formation #1

Physical and chemical weathering processes are important in the formation of soil. Two processes are Root wedging, and acids from decaying organic matter mix with groundwater and aid in dissolving rocks. Soil is the mixture of rock particles and organic matter on Earth's surface that supports rooted plants.

Form of Physical Weathering #3

Physical weathering also occurs when rock particles grind against rock in a process called abrasion. Abrasion occurs as sediments moved by ice, gravity, running water, or air come into contact with other rocks. The characteristic rounded shape of rocks from river beds and beaches is caused by abrasion.

Soil formation #3

Soils can also be transported into an area from another place—usually by wind, by moving water, or by the moving ice of a glacier. Already-formed soils are often directly transported while in other cases sediments are transported by erosion, which upon deposition becomes the parent material for soil development. The soils covering most of New York State formed from sediments deposited by glaciers during the most recent ice age, or by water melted from these glaciers. In the last 10,000—15,000 years, soil-forming processes have worked on these transported sediments to produce the present-day soils.

Soil formation #2

Soils can form in place from a parent material, such as bedrock. Over time, soils develop horizontal layers with a distinctive profile. Soils formed in place have some characteristics of the parent material from which they formed. However, the most important factor in determining the type of soil that forms in a particular place is the area's climate.

Kettle lake

Sometimes as a glacier melts back, it leaves blocks of ice in the terminal or ground moraine. When these blocks of ice melt, they leave behind circular depressions called kettle holes or kettles. If these kettles intersect the water tables, they will become filled with water and are then called kettle lakes.

Floodplain #2

Streams make their deposits in different locations. In the stream course itself sediments are deposited on the inside of the meanders where stream velocity is slow. When a stream floods and overflows its banks, some of the sediment forms a mound at the edge of the river called a levee, but most of the sediment is spread over a relatively flat region to the sides of a stream forming a floodplain

Finger lakes

Streams slowly change their characteristics over time in response to changes in elevation, gradient, volume of water, and available sediments. A typical stream starts with a finger lake. Finger lakes are bodies of water in U-shaped valleys carved by glaciers and often partly dammed at one end by a pile of glacially deposited sediments.

Watershed

The area of land drained by any one stream is called its watershed, or drainage basin. A region of higher land that separates one watershed from another is called a divide. In the United States, the Continental Divide follows the crest of the Rocky Mountains. Watersheds on the eastern side of the continental divide drain toward the Atlantic Ocean, while watersheds on the western side drain toward the Pacific Ocean.

Physical Weathering

The breakdown of rock into smaller pieces without chemical change is called physical weathering.Physical weathering occurs when frost action, plant root growth, pressure changes, or abrupt temperature changes cause rocks to crack apart.

Chemical Weathering

The breakdown of rock through a change in mineral or chemical composition is called chemical weathering.

Weathering

The chemical and physical breakdown of rocks at or near Earth's surface is called weathering. Weathering occurs when rocks are exposed to air, water, pressure changes, and the actions of living things. The origins of most of Earth's landscape features and soils can be traced to the weathering of exposed rocks.

Driving force of erosion #1

The driving force for most types of erosion comes from gravity. Rocks and sediments at higher elevations have gravitational potential energy, part of which changes into kinetic energy when gravity pulls them downward.

Velocity of the erosional system

The faster a stream flows, the larger size sediments it can carry. If the stream flows below a certain velocity, it will deposit the sediments it can no longer carry.

Stream velocity #2

The last factor is stream channel shape—the shape of the bed of rock or loose materials that confine the stream. A wide and flat stream channel has a large surface in contact with moving water—and therefore, a large amount of friction is present to slow down the stream. In contrast, a semicircular stream channel shape results in less friction and greater stream velocity.

Deposition #1

The process by which sediments are released, settled from, or dropped from an erosional system is deposition, or sedimentation. Deposition includes the releasing of solid sediments and the process of precipitation— the releasing of dissolved minerals, hardness, or salts from a water solution to form chemical sedimentary rocks.

Factor affecting the rate and type of Weathering #4

The rate and type of weathering in a given location are greatly influenced by climate. Chemical weathering is most pronounced in warm, moist climates. Generally, the higher the average temperature and precipitation, the more rapid the chemical weathering. In cold climates, frost action is the most common form of weathering. Frost action is especially intense in moist climates with temperature variations that lead to repeated cycles of freezing and thawing.

Maximum stream velocity

The region of maximum velocity shifts when the stream changes direction. When the stream channel is straight, maximum velocity occurs at the center of the stream. When the stream channel curves, the region of maximum velocity shifts to the outside of the curve because of inertia. Velocity also varies with depth. It is greatest just below the surface and least near the stream bed, or stream channel bottom.

Delta #2

The sediment that makes it to a lake or ocean will be deposited. This deposition at the end of a stream, with characteristic horizontal sorting, is a delta. If there are strong ocean or lake currents, a delta may not form because the velocity of the water is not reduced enough at this location.

Characteristics of sediments (shape)

The shape of a particle helps determine how fast it will be deposited from wind or running water. All other factors being equal, the more rounded a sediment, the faster it will settle out. The more flattened it is, the greater its resistance—caused by friction—to deposition.

U-shaped valley

The wide, thick ice of a glacier erodes its confining valley walls as much as it does the rock beneath it. The result is a characteristic glacial U-shaped valley.

Glacial grooves and glacial parallel scratches

These gouging and sanding actions produce glacial grooves and glacial parallel scratches, along with more loose sediments. The direction of exposed glacial grooves and scratches on bedrock shows the direction of former glacial movement.

Form of Chemical Weathering #3

Water can also combine with carbon dioxide from air to form carbonic acid. Carbonic acid in surface water and ground water easily dissolves some rocks—especially limestone and marble. This dissolving of limestone and marble often results in unique features that include sinkholes and caves, and indirectly, in the formation of limestone terraces and limestone "icicles."

Breaking waves

Waves passing through deep water cause brief circular water movements. However, when waves enter shallow water near the shore, they drag against the bottom. The waves then become unstable and water rushes toward the shore as breaking waves, or surf.

Sediments #2

Weather conditions, the actions of living things, and other factors can make Earth's surface rocks break down into smaller particles. Moving water or wind can then carry the rock particles away as sediments. Eventually, sediments are deposited in environments such as the ocean floor, where they become part of sedimentary rocks.

Erosion

Weathering of rock produces particles that are transported as sediments through the process of erosion. Over time, erosion shapes and lowers Earth's surface. Sediments displaced from their source are evidence of erosion.

Factor affecting the rate and type of Weathering #2

Weathering results in the formation of rock particles of different sizes. When the rock particles are smaller, the total surface area per unit volume exposed to weathering is greater. Therefore, the rate of weathering is faster. To understand the effect of increased surface area, consider what happens when you add sugar to a drink. Granulated sugar dissolves more quickly than an equal mass of sugar cubes because the granulated sugar has a greater surface area exposed to the liquid around it.

Glacial erosion

When a glacier moves over the land, loose rocks and other materials beneath it freeze into the ice and are dragged along. Many of the sediments carried by a glacier are carried on or near its surface. These sediments are generally rock fragments broken off from valley walls by frost action and deposited onto the glacier by mass movements. Often the rock fragments are very large—up to the size of a small house. Glacial sediments can be carried hundreds of miles.

Graded bedding

When a mixture of sediment sizes in water settles out rapidly, a horizontal bed, or layer, develops with the sediment size decreasing from the bottom to the top. Such an arrangement in a sediment layer is called "graded bedding."

Deposition and erosion on the beach

When a shoreline has a natural or human-made projection out into the ocean— such as a peninsula or pier—sand is deposited on the side of the projection facing an oncoming longshore current. This deposition occurs because the water slows down when it reaches the projection, and the sand settles out. The side of the projection facing away from the longshore current usually gets eroded because it is not protected by the sand deposits.

Mass movement deposition

When an avalanche or other type of mass movement hits the ground and stops moving, the sediments it was transporting are deposited as a landform feature of Earth's surface. These features are usually composed of unsorted and unlayered sediments. Depending on the history of the sediments, many will not be very rounded in shape but will often have sharp sides.

Stream

When running water erosion is confined to a channel, a stream exists.

Sand abrasion

When sand grains collide, sandblasting also results in abrasion, and the frosted, or pitted, appearance of the sand grains themselves.

Erratics

When sediments are deposited, they may differ greatly from the bedrock in their new location. Such contrasting sediments, called erratics, are found in much of the northern United States and most of New York State.

Horizontal Sorting

When the velocity of a wind or water erosional system gradually decreases, such as when a stream flows into the ocean at a delta, the larger, denser, and more rounded sediments settle out first. This results in layers with horizontal sorting, in which the sediment size, roundness, and density generally decrease in the direction toward which the erosional system was moving.

Formation of sandbars

When the waves are more powerful, such as during storms, the beach tends to erode more and the sand is carried back into the ocean. There it is usually deposited as underwater bars parallel to the shoreline. Sand is added to these features by the longshore currents. These longshore currents transport sediment—sand—and when the velocity of the water slows, deposition creates various types of depositional features such as sandbars. In the zone of breaking waves, deposited sediments can create a series of mounds called a sandbar.

Mass movement deposits

When there is mass movement, such as a rock fall, landslide, or avalanche, the sediments are usually dumped together in a random deposit that is unsorted and unlayered, similar to glacial deposits.

Beach

When wind-generated ocean or lake waves slow down as they drag bottom approaching the shore, they tend to move sediment towards shore. This wave movement towards the shore often builds up a strip of sediment at the coastline called a beach.

Wave and current erosion

Where lake or ocean waters meet land, waves and currents act as agents of erosion—creating unique landscape features. Winds transfer energy to the surface of lakes and oceans, creating waves.

Stream energy #2

Where the slope of the stream is steep, the transformation of energy occurs most rapidly, the stream has its greatest velocity, and the system has its greatest kinetic energy. Where the slope is small, the rate of energy transformation decreases, the stream slows down, and the kinetic energy of the system decreases. At the mouth of the stream, the velocity drops to zero, and the system has zero kinetic energy. Since the system has less potential energy because of its lower elevation, there has been a net loss of energy between the source and the mouth.

Outwash plain

Wherever glaciers melt, running water will carry sediments from the glaciers to produce layered and sorted sediment deposits when the water slows down or stops. One such feature is an outwash plain—a broad delta-like feature.

Deposition and erosion energy changes #1

Wherever the kinetic energy of the system is large, erosion is the dominant process. Where the kinetic energy is small, deposition is the dominant process. Thus, erosion occurs in regions of steep slope or high discharge, and deposition occurs in regions of gentle slope or low discharge. Deposition is particularly rapid at the mouth of the stream, where the kinetic energy becomes zero. Stream velocity is faster at the outside of curves, or meanders, and slower at the inside. Therefore, erosion usually occurs at the outside of meanders, and deposition occurs at the inside.

Form of Physical Weathering #4

Root wedging, roots of plants can grow within cracks in the rocks and increase the crack size, leading to crumbling of the rock.

Sandblasting

Sandblasting occurs when winds blow sand or silt grains against rocks and other objects. The pelting by the grains can erode, or abrade, rocks in a manner similar to the process used to clean brick and stone buildings. Since wind can usually lift sand grains only about one meter into the air, the lower portions of exposed rocks become more eroded than the upper portions.

Sediments #1

Sediments are a naturally occurring material that is broken down by the process of weathering and can be transported by the process of erosion. Sediments can be the size of a grain to the size of a boulder.

Dynamic equilibrium of a stream

Since all sediments picked up by the stream during erosion must eventually be deposited, the system is in a state of dynamic equilibrium. Although erosion and deposition are occurring continuously, the rate of erosion equals the rate of deposition by the system as a whole. If a flood occurs, a stream will erode—pick up and transport—more sediment, but it will also deposit an equally increased volume of sediment, thus establishing a new balance of equilibrium.