Weathering and Erosion

How long does soil take to form?

soil takes 100-400 years to form 1 cm. It's important humans conserve it. Road sult can pollute soil. Exposed soil can quickly erode.

Waves

- Waves are caused by wind -water does not move forward with waves but rather circulates in small circles. - waves carry energy which is released when waves break - Waves break when they "feel bottom" in shallow water (less than 1/2 wavelength) - waves in the break zone refract (bend) and travel parallel to the shoreline - released energy causes changes in beach sediments. It abrades them. The released energy can change the shoreline by transporting sand in the zone of longshore transports. That is, in the surf zone. - beaches come and go in natural cycles - man tries to control the shoreline by building jetties but this often causes other problems such as erosion or deposition in other places.

The influence of human activity on landscape

- forming and construction can accelerate erosion -strip mining removes soil layers to take minerals from the bedrock. - much rock and soil is moved by people and his machinery - man must practice conservation methods such as contour plowing and land reclamation

The influence of geologic factors

- rocks that resist weathering and erosion are called competent rocks. -competent rocks from higher portions of the landscape including mountains, plateaus and escarpments (cliffs) - softer rocks and rocks that have cracks underly valleys and other low areas - streams generally follow zones of weakness such as less competent rock, fault or joints

The oceans and coastal processes

- sea water covers 71% of our planet to an average depth of 4km - the deepest ocean is 1 mile deeper than mt. Everest is high! - Most sediments deposited on land will later end up in the ocean - simple salts are carried to the ocean in solution (dissolved) the most common kind of salt is NACL (table salt) - when salts become too concentrated- usually as a result of evaporation to remain dissolved they are deposited as sediment.

Erosion by moving ice

-Glaciers are large masses of moving ice -glaciers form when more snow accumulates in winter than melts in summer - Glaciers erode and abrade because of the rock that they carry embedded in them. They striate and groove bedrock -continental glaciers deepen and widen valleys parallel to the direction of its flow. They grind hills leaving them rounded and smooth. -Valley glaciers flow like a river but more slowly. The ice flows most rapidly near the center of the ice. - Glaciers make U-shaped valleys out of V-shaped river valleys Glaciers leave behind piles of unsorted sediments called till when they melt. These sediments include pieces too large for water to carry. New york state has undergone 4 periods of glaciation in the last 2 million years Soils in Newy York state and globally are more commonly transported than residual. agents of erosion include moving water, wind, glaciers, and gravity acting alone.

Glaciers

-Ice forms under the weight of accumulated snow. -Flow downhill outward from the place where they are the thickest. - Flow slowly at a rate of several cms to m a day. - Continental glaciers, aka ice sheets are responsible for most nys glacial features - It is the rock carried by a glacial that cause most glacial sculpting - In nys glacial flowed mostly from N to S and then retreated from S to N only when melting back exceeded southward flow.

Deposition by glaciers

-deposition occurs when a glacier melts -rounding (sub-rounded) striations (scratches), and presence of glacial erratics characterize glacial deposits. - glacial erratics are large boulders, often found high above sea level and often different in composition from the bedrock on which they rest.

Glacial features

-kettles and kettle lakes were formed where large buried ice blocks melted. -Kames are deltas formed by meltwater at glacial edges -Eskers are ridges formed by meltwater deposition within an ice tunnel.

ARID DRY CLIMATE

-sharp, angular features -thin soils with little humus -physical weathering dominantes promoting large angular gains and structures -little vegetative cover and much erosion when it does rain. -large areas of exposed bedrock and steep rock faces -most streams are dry except after a storm

Shores

-the edges of oceans-shores are places of rapid change - change is caused by wave action and longshore currents

Particle size

-the larger the particle, the faster it settles. - some very small particles remain in solution or suspended - these particles only come out if the solution becomes saturated Example: when seawater evaporates and leaves water too rich in salt. If more water evaporates then salt is forced out of the solution, forming a precipitate. This process is called precipitation

Rates of sedimentation are affected by:

-the size, shape, and density of the sediments. -the speed of the transporting medium

Types of Mass movement:

1. Falls- free fall of detached, individual pieces, 2. slides- when materials stay together and slides downslope along a surface. EX: Mudslides (more water than a landslide) and slump- when material moves along a curved surface of rupture. 3. Flows- When material moves downslope as a thick liquid. Ex: earthflow 4. Hillside creep- very slow movement- makes posts crooked.

types of landscapes

1. Mountain landscapes 2. plateau landscapes 3. plains landscapes -each has its own geologic structures and topographic relief

Weathering starts on the surface and becomes deeper with time as do soils which also become deeper with time.

1. The C- horizon (weathered rock) forms first 2. The A-horizon forms next. This horizon includes the root zone and humus 3. The B-horizon is the last to form. Soils are considered mature only after there is a B-horizon present. The B- horizon contains the build-up of minerals that have leached from the A-horizon.

Types of glacial deposits

1. Till-unsorted material deposited directly by moving ice. 2. outwash- sorted and layers materials deposited by stream of meltwater from the glacier.s

The shape (topography) and composition of a landscape region are caused by:

1. climate 2. bedrock composition 3. geologic structures 4. human activities boundraies between landscapes are often distinct

Landscape

A region on the earth's surface in which physical features such as hills, valleys, and streams are related by common origin.

deposition

Also known as sedimentation. The process of laying down of sediments by agents of erosion.

Nys and the ice ages

As recently as 20,000 yrs ago most of NY was covered with a continental ice sheet. This was the last of the 4 ice ages that occurred during the last 2 million years. There were others before that.

What activities contribute to soil formation?

Chemical weathering, physical weathering, plant and animal activity

Deposition in streams

Deposition in the slower sections of a stream can cause the development of features such as sandbars. Rivers used for transport may need to be dredged to stay deep enough for navigation.

Factors that affect the rate of weathering

Exposure- surfaces must be exposed to air and water. Particle size- smaller particles have more exposed surface area per volume. Mineral composition- minerals differ in their resistance to weathering. Climate- warm, moist climate- chemical weathering predominates. Cold, moist climate- physical weathering predominates due to frost action

What is required for chemical weathering to take place?

Requires heat energy and water to make chemical reactions take place therefore chemical weathering occurs most rapidly in warm and moist climates

Examples of chemical weathering

Feldspar reacts with water to form clay minerals. Iron reacts with O2 to form iron oxide

What's driving force of erosion

GRAVITY=DRIVING FORCE OF EROSION

Influence of climate on landscapes

MOIST, HUMID climate -rounded features - development of well balanced mature soils -abundant plant cover slows erosion -many small streams that flow most of the time

examples of minerals that are more resistant to chemical weathering

Quartz resists weathering. But limestone weathers quickly in the presence of acidic water. rainwater can be naturally acidic because it absorbs carbon dioxide from the atmosphere. It can be acidified due to air pollution.

Soil classification by origin:

Residual soils are soils formed in place from the bedrock beneath them. As time goes on the nature of a soil depends less on the nature of the parent material and more upon the climate of the area. Transported soils that formed from the sediments of bedrock that was transported from some other location.

The size that can be carried depends on what?

The size of the particles that can be carried depends on a stream's velocity. We can estimate the velocity of a stream by looking at the size of the sediments that can be carried.

Evidence of erosion

The evidence of erosion is transported sediment. sediment that differs from the bedrock beneath them

Deposition by gravity

When gravity acts alone, sediments are unsorted and angular. Often at the base of cliffs you will find unsorted piles of sediments known as talus.

chemical weathering

When rocks uplifted and exposed at the surface interact chemically with the atmosphere and hydrosphere. Changes the chemical composition of the rock.

Vertical sorting

When sediments fall through still water they sort from bottom to top. - the largest, roundest, most dense particles will be on the bottom, while the smallest, flattest, less dense particles will be on top.

Sorting of sediments: Horizontal sorting

When transporting medium slows down, it begins to deposit its sediments. -The largest particles will be deposited first. Example: when a stream enters a body of water it slows down so the largest, roundest, most dense, particles will be dropped first, near the shoreline. The smallest, flattest, least dense particles will be carried farthest.

Deposition by wind

Wind sorts sediments by size. Hills of wind blown sand or dunes may be formed on beaches and deserts. Dunes may have different layers within them made up of different sized particles. Layers that meet at different angles create a feature known as cross-bedding.

Stream stages

Youthful stream- characterized by steep gradient, rapids, waterfalls, and V-shaped valleys. the stream is downcutting its bed Mature Streams- characterized by a gentle slope and the development of some meanders. Old Age Stream- characterized by strongly developed meanders causing the formation of oxbow lakes.

Graded beds

a type of vertical sorting where a series of depositional events have occured. Earthquakes can cause underwater landslides or turbidity currents that lead to the development of graded beds. A sudden change in grain size from fine to coarse separates one graded bed (& event) from another

Terminal moraines

are piles formed where the ice sheet stopped its forward advance. Ex: 1. long island is made of a series of terminal moraines. 2. The finger lakes were formed terminal morines dammed glacially deepened and widened former river valleys

Plateau landscapes

are relatively flat or rolling hills with deep cut stream valleys. They are commonly underlain by FLAT layers of sedimentary rock. -Have less relief than mountains but more than plains -unlike mountains plateaus are underlain by FLAT layers

Depositional features: Drumlins

are streamlined hills formed by glaciers moving up and over mounds of till (unsorted glacial debris)

Physical weathering

changes the rock's size or shape WITHOUT changing its chemical composition

Abrasion (physical weathering)

collisions between rocks as they bump and rub against one another wear down rock surfaces. Agents of abrasion include running water, wind, glaciers, gravity

Particle density

denser particles settle more quickly than less dense particles of the same size and shape. SETTLING RATE AND SETTLING TIME ARE INVERSELY PROPORTIONAL! -Sediments that settle at a faster rate require less time to settle

Agents of erosion

erosion occurs due to the action of running water, wave action, wind, moving ice, and human activity. All of these act under the influence of gravity

Erosional features

glaciers act like sandpaper grinding and smoothing bedrock surfaces (glacial polish) Striations-parallel grooves scraped into the rock surface by rocks within the glaciers. Glaciers deepened and widened river valleys making them more U-shaped

New york state

has mostly immature, transported soil because the glaciers scoured the bedrock clean and then left new parent material in place that developed into soil. As a result the B-horizon is often missing from soil profiles and the weathered rock does not resemble the bedrock beneath it.

Mountain landscapes

have the greatest relief between peaks and valleys. -can be made up of a variety of rock types including igneous,metamorphic, and sedimentary - are common where converging tectonic plates collide -underlying rock layers are folded and faulted

Plain landscapes

have the least topographic relief. -are generally flat and a low elevations. -are commonly underlain by flat layers of sedimentary rock -underlying layers are FLAT sedimentary rock

Soil formation

soil is a mixture of weathered rock and humus(organic material) that normally covers bedrock.

Streams move sediments in different ways

in solution- dissolved particles are carried this way. These particles are too small to be filtered out. In suspension- these particles are too small to settle out on their own but can be filtered out. Colloids and clay-sized particles are carried in suspension In traction- by rolling and bouncing (saltation) along the bottom Low density particles especially organic remains are carried by FLOATATION

Erosion

involves the moving of sediments from their place of origin and their transportation elsewhere.

Stream velocity

is controlled by slope (gradient) and discharge (amount of water flowing in a stream) and channel factors (the channel is the part usually covered by water)

Where is the fastest moving water in a stream

is found in the center away from its bed and below the surface. Along curves (meanders) the fastest moving water swings to the outside of the curve, and slower moving water is on the inside of the curve, where deposition may take place.

Erosion by running water

is the dominant agent of erosion worldwide and in NYS today. Always dominantes in moist areas

what is velocity related to?

it is directly related to gradient, discharge, and roundness and smoothness of a stream's channel- a rounded, smooth channel offers less resistance than a flat or rough (having many rocks, boulders) channel. A stream has the most energy when these are greatest. Streams have the most power to erode when in flood.

stages of stream development- stream valley formation

most sediments come from bedrock of surrounding slopes. stages indicate characteristics not age. A stream can be in more than one stage along its length.

Erosion by wind

occurs mainly in dry (arid) regions such as deserts. Along beaches. Wind can pick up small particles such as silt, clay, and sand leaving larger particles behind resulting in the desert pavement. Wind can also erode by abrasion. Particles carried "sand-blast" surfaces they collide with and carve away at them forming ventifacts

Root action (physical weathering)

occurs when plant roots grow and gradually expand cracks in rocks.

When does weathering occur?

occurs when rock formed within the earth is uplifted and exposed to wind, water, and biolog]ical processes.

frost action (physical weathering)

occurs when water gets into cracks in rocks and expands as it freezes. Repeated freezing and thawing breaks down the rock. Important in moist climates where the temperature frequently alternates above and below freezing.

Sediments

rock fragments of any size- they are the product of weathering.

Particle shape

round particles settle more rapidly than flat, angular, irregularly shaped particles. Flatter and more angular particles have more resistance as they fall through water.

Weathering

the breakdown of rock due to physical or chemical changes.

animals (physical weathering)

they burrow and expose new rock surfaces

What do soil characteristics depend on?

they depend on parent rock and local climate.

Mass movement

when materials move downslope as a direct result of gravity. Landslide is another word for mass movement