Esci: Exogenic Processes of Weathering, Erosion & Deposition

Weathering

Weathering

• involves the physical breakdown (disintegration) and chemical alteration (decomposition) of rock at or near the Earth’s surface

Mechanical Weathering

• Accomplished by physical forces that break the rock into smaller and smaller pieces without changing the rock’s mineral composition.

• the disintegration of Earth's materials makes detrital sediments

Frost Wedging

• When water enters the joints, alternate freezing and thawing episodes pry the rock apart.

• After water works its way into the cracks in the rock, t__he freezing water enlarges the cracks, and angular fragments are eventually produced__.

Salt Crystal Growth

• Force exerted by a salt crystal that forms as water evaporates from pore spaces or cracks in rocks can cause the rock to fall apart.

• Infiltration of salty waters on rocks or soils from groundwaters or salty seawater.

Sheeting

• Also known as exfoliation, it is caused by the expansion(pressure release) of crystalline rock as erosion removes the overlying material(overburdened rock)

Abrasion

• Wearing away of rocks by the constant collision of loose particles

• This can be due to water, wind, or ice.

Biological Activity

• Plants and animals as agents of mechanical weathering

• Wedges in rocks and soils form through plant growth (rooting) and motor activities of animals and even humans (like burrowing or shoveling).

Chemical Weathering

• Involves a chemical transformation of rock into one or more new compounds.

• Decomposition of rocks and minerals by chemical processes

Dissolution

• dissociation(splitting) of molecules into ions

• the process by which a mineral completely dissolves in water or other acidic solutions

• a common example includes the __________ of calcite and salt

Oxidation

• reaction between minerals and oxygen dissolved in water

• the reaction of oxygen with iron-bearing minerals in rock.

Hydrolysis

• change in the composition of minerals when they react with water

• occurs when silicate minerals react with water so that the mineral recombines with the water molecule to form a new mineral.

• For example, consider the mineral potassium feldspar

Spheroidal weathering

• A form of chemical weathering where a generally spherical boulder is cracked & split off into curved layers on a much smaller scale

Climate

? Cold and dry

? High temperature and high rainfall

A factor that affects weathering:

• The presence of water which is an important chemical weathering agent increases the rate of weathering.

• High temperature enhances chemical reactions.

? What climate causes a slow rate of chemical weathering

? What climate causes a high rate of chemical weathering

Rock Type

A factor that affects weathering:

• The minerals that constitute rocks have different susceptibilities to weathering.

• Those most stable to surface conditions will be the most resistant to weathering.

Rock Structure

A factor that affects weathering:

• rate of weathering is affected by the presence of joints, folds, faults, bedding planes through which agents of weathering enter a rock mass.

Topography

? Steep slopes

? Gentle slopes

A factor that affects weathering:

• Weathering may occur more quickly on a steep slope than on a gentle one

? In what kind of slope is physical weathering faster

? In what kind of slope is chemical weathering faster

Time

A factor that affects weathering:

• Longer exposure to weathering agents could mean a higher degree of weathering processes have occurred. The rock has been weakened; therefore, easier to be a break.

• Length of exposure to agents of weather determines the degree of weathering of a rock

Erosion

• the incorporation and transportation of material by a mobile agent such as water, wind, or ice

Deposition

• the settlement of material on a definite location; the inability of a mobile agent to transport deposits material.

• Running Water

• Ocean or Sea Waves

• Groundwater

• Glacier

• Wind

• Gravity

• What are the basic agents that drive sediment transport?

Hydrologic Cycle

Drainage basin

• the area drained by a stream and its tributaries

Divides

• boundaries between drainage basins

Laminar flow

• fluid travels smoothly or in regular paths

Turbulent flow

• irregular fluctuations of liquid

• the speed of water is continuously undergoing changes in direction & magnitude

Overland flow

Encompassed by Running Water

• surface run-offs

• water flow down to a drainage basin due to a drainage divide, form rills and gullies on the surface due to erosion(rill & gully erosion)

• can erode before forming rills and gullies by sheet erosion

Streamflow

Encompassed by Running Water

• water flow in drainage basins(valley formation)

• turbulent flow of water is usually in river channels

Velocity

A factor affecting stream

• dictates the ability of a stream to erode & transport

• controlled by gradient, channel size & shape, channel roughness and the amount of water flowing in the channel

Gradient

A factor affecting stream

• slope of the stream expressed as the vertical drop of a stream over a specified distance

• reserves much more enrgy the steeper it gets

Channel

A factor affecting stream

• stream path; straight channel can cause smooth stream(smooth erosion) while curved/banked channel can slow the stream and make it turbulent

Discharge

A factor affecting stream

• volume of water passin through a cross-section of a stream during a given time

• as the discharge increases, the width of the channel, the depth of flow or flow velocity increase individually or simultaneously

Slows the velocity

• What happens to the velocity when a channel is widened by soft rock and becomes rough & boulder strewn?

• what happens to the velocity when the channel is wide & shallow, increasing friction?

Stream velocity increases

• What happens to the velocity when a landslide narrows a channel?

• What happens to the velocity when a channel is semicircular?

• What happens to the velocity when bridge, piers or other obstructions are put up?

Headward Erosion

Styles of erosion

• makes a river longer

• happens near its source

• surface run-off and flow cause erosion at the point where the water enters the valley head

Vertical Erosion

Style of erosion

• makes a river channel deeper

• this happen more in the upper stages of a river

Lateral erosion

Style of erosion

• makes a river wider

• this occurs mostly in the middle and lower stages of a river

Quarrying

Erosion process in running water

• involves the removal of blocks from the bed of the channel

Abrasion

Erosion process in running water

• bed & banks of a bedrock channel are ceaselessly bombarded by particles carried into the flow

Corrosion/Solution

Erosion process in running water

• a procces in which rock is gradually dissolved by the flowing water

Dissolved Load

Running Water: Transport sediment

• solution

• transportation of dissolved mineral which is moved and dispersed in stream

• usually came from groundwater

Suspended Load

Running Water: Transport Sediment

• suspension

• fine sediments(such as clay) transported in streams as suspended sediments

• usually came from flooding/run-offs

Bed Load

Running Water: Transport Sediments

• coarse grains

• transportation by traction(rolling of gravels such as boulders) and saltation(skidding or jumping movements of smaller gravels such as pebbles)

Bedrock Channel

Running Water: Channel Formation

• channel which consists and generally formed by rocks whereas its pattern is geologically structured

• definite and uniform structure

Straight Channel

Running Water: Channel Formation; Bedrock Channel

• form where a stream erodes sediments in a constant patter without drstic change in its path/flow

Alluvial Channel

Running Water: Channel Formation

• watewr path whereas it has no definite patter and it changes its structure

• composed of unconsolidated sediments

Braided Channel

Running Water: Channel Formation; Alluvial Channel

• form where alarge portion of a stream’s load consists of coarse material(sand & gravel) and the stream has a highly variable discharge

Meandering Channel

Running Water: Channel Formation; Alluvial Channel

• form where streams that transport much of their load in suspension generally move in sweeping bends

• River valleys, waterfalls, potholes, terraces, gulley/rills

• Meanders(exhibit erosion & depositional features), oxybow lake, peneplain

• What are the of Erosional Landforms from Running water as an agent of erosion

• Alluvial fans/cones, natural leeves, deltas

• What are the Depositional landforms from running water as an agent of erosion?

Deltas

Running Water: Deposits According to Agents of Erosion

• form where sediment-charged streams enters the realtively still water of a lake, an inland sea, or the ocean

Natural Levees

Running Water: Deposits According to Agents of Erosion

• meandering rivers that occupy valleys with broad floodplains, tend to build _____ ______ that parallel their channels on both banks

Alluvial Fan

Running Water: Deposits According to Agents of Erosion

• Are fan-shaped deposits that accumulate along steep mountain fronts

• When a mountain stream emerges onto a relatively flat lowland, its gradient drops and its deposits a large portion of sediment load

Waves

Ocean or Sea Waves

• energy transported to a medium

• are caused by energy transferred by wind or storm in the ocean’s surface

• Wave Height

• Wavelength

• Wave period

Characteristics of a Wave

• What do you call the vertical distance between trough and crest?

• What do you call the horizontal distance between successive crests(or troughs)?

• What do you call the time it takes one full wave to pass a fixed position?

• Wind speed

• Length of time the wind has blon

• Fetch or distance that the wind has traveled across open water

• What are the factors that affect the Height, Length & Period of a Wave?

Hydraulic Action

Shoreline Erosion Process of Ocean/Sea Waves:

• Rock wedging and disintegration due to wave slap

Abrasion

Shoreline Erosion Process of Ocean/Sea Waves:

• the sawing and grinding action of the water armed with rock fragments

Corrosion

Shoreline Erosion Process of Ocean/Sea Waves:

• dissolution of rocks due to constant wave current

Wave Refraction

Transportation by Waves and Currents:

• bending of waves making wave front parallel to the shore

Longshore Current

Transportation by Waves and Currents:

• erosion of sediments/soils by angled/oblique wave to the shore

Rip Current

Transportation by Waves and Currents:

• Concentrated movement of water that flow in the opposite direction from breaking waves

• Wave-cut Cliffs

• Wave-cut Platforms

• Marine Terraces

• Sea Arches

• Sea Stacks

• What are the Erosional Features from Ocean/Sea Waves as an agent of erosion

• Beach

• Spits

• Baymout bars

• Tombolo

• Barrier Island

• What are the Depositional Features from Ocean/Sea Waves as an agent of erosion

Glaciers

• a moving body of ice on land that moves downslope or outward from an area of accumulation

Ice Sheets(continental glaciers)

Types of glaciers:

• Cover large areas of the land surface

• unconfined by topography

• cover Antartica and Greenland

Outlet glacier

• when a glacier flows out of an ice sheet, ice cap or icefield

Valley(Alpine) Glaciers

Types of glaciers; Ice Sheets:

• bounded by vallewys and tend to long and narrow

• can be formed when an outlet glacier forms and slides away from an icefield

• Can also be formed on their own, starting from high up on a mountain range and flowing down within the steep V between two peaks

Ice Shelf

Types of glaciers:

• a thick slab of ice, attached to a coastline and extending out over the ocean as a seaward extension of the grounded ice sheet

Cirque Glaciers

Types of glaciers:

• snow that accumulates in small depressions on the side of a mountain, eventually compacting into glacier ice

• when the glaciers are built up and shifted, they erode the depression to form bowl shaped valleys called corries or ______

• may sometimes accumulate enough ice to spill over and form valley glaciers

Firn

Glaciers: Glacial Formation

• a recrystallized snow that is dense and is in granular form with a texture like coarse sand

• basic structure that is pressurized to form glacial ice

• plastic flow

• basal slip

Glaciers: Glacial Movement

• Glaciers move to lower elevations by _______ ____ due to great stress on the ice at depth;

• and _____ ____ facilitated by meltwater which acts as a lubrican between the glacier and the surface over which it moves

• Plucking

• Abrasion

Glaciers: Glacial Erosion

• What do you call lifting piecies of bedrock beneath the glacier?

• What is the grinding and scraping by sediment already in ice called?

• Glaciated Valleys

  • Glacial Through

  • Truncated Spurs

  • Hanging Valleys

  • Paster Noster Lake

  • Cirque

  • Tarn

  • Col

• Aretes and Horns

• Rouches Moutonnees

• What are the landforms created by glacial erosions?

Glacial Till

Glaciers: Glacial Deposits

• deposited as glacial ice melts and drops its load of rock fragments

Stratified Drift

Glaciers: Glacial Deposits

• deposited by the glacial meltwater and thus has experienced the sorting action of water

Wind

• a relatively insignificant erosional agent

• Dryness and scant vegetation are important prerequisites for it to be an effective errosional force

Dunes(Sand Deposits)

Type of Wind Deposits:

• Hills or ridges of wind-blown sand

Loess(Silt Deposit)

Type of Wind Deposits:

• Extensive blankets of silt that were once carried in suspension

Barchan

Wind: Type of Sand Dune

Transverse

Wind: Type of Sand Dune

Barchanoid

Wind: Type of Sand Dune

Longitudinal

Wind: Type of Sand Dune

Parabolic

Wind: Type of Sand Dune

Star

Wind: Type of Sand Dune

Groundwater

• represents the largest reservoir of freshwater that is readily available to humans

• erodes sediments chemically rather tham mechanically(Weathering and movement of solution)

Zone of soil moisture

Distribution of Groundwater

• area where water is molecularly atrracted and suspends

Unsaturated(Vadose) Zone

Distribution of Groundwater

• contains both air and water

• water cannot be extracted through wells

Saturated(Phreatic) Zone

Distribution of Groundwater

• where all the open spaces in sediments and rocks are completely filled with water

Groundwater

Distribution of Groundwater

• water present in the phreatic zone

Water table

Distribution of Groundwater

• the upper limit of the phreatic zone(boundary with the valdose zone; “water level”)

Capillary fringe

Distribution of Groundwater

• Just above the water table

• zone where water can penetrate

Graining Streams

Stream-Groundwater Interaction:

• inflow of groundwater through the streambed

• higher elevation of water table

• receive water from he groundwater system

Losing Stream

Stream-Groundwater Interaction:

• lower elevation of water table

• water from streambed follow down to groundwater

• can be connected ot disconnected

• provide water to the groundwater system

• (disconnected) may form a buldge in the water table when it is separated from the groundwater system by the unsaturrated zone

Porosity

• Factor affecting the storage and movement of groundwater

• percentage of total volume of rock or sediment containing pore spaces

Permeability

• Factor affecting the storage and movement of groundwater

• the ability to transmit fluid

Aquitards

• Factor affecting the storage and movement of groundwater

• impermeable layers that hinders water movement

  Ex. clays have mcuh smaller pores

Aquifiers

• Factor affecting the storage and movement of groundwater

• Permeable layers that transmit groundwater freely

  Ex. Sand & gravels have much larger pores

Specific Retention

• Factor affecting the storage and movement of groundwater

• the ratio of the volume of water that a given body of rock or soil will old against the pull of gravity to the volume of the body itself

Specific Yield

• Factor affecting the storage and movement of groundwater

• also known as the drainable porosity

• is a ration, less than or equal to the effective porosity

Recharge area

Flow system

• water flow underground that replenishes water