Esci: Exogenic Processes of Weathering, Erosion & Deposition

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 c***racked & 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

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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