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Test 3 Geology

Terms in this set (90)

Competence:
A measure of the largest particle size that is in motion. Increases during floods.
A measure of the largest particle size that is in motion. Increases during floods.
Groundwater Erosion
Based not velocity, but no the effectiveness of chemical weathering. This will affect rocks such as limestones, dolostones, and rock gypsum much more than sandstones, shales, etc.

Erosion is further aided by preexisting fractures (faults and joints) and proceeds most rapidly at or near the water table.
Karst
Areas, where the land surface has been greatly modified by the collapse of caves, are said to have karst topography. Sinkholes, disappearing streams and springs are common features.

Karts topography usually appears in limestone regions where cave development is already in an advanced state.
Glaciers
They form when snow accumulates at a greater rate than it melts, converts to granular form called firn, then compacts into glacial ice. Glaciers flow when depth exceeds - 50 meters.

Glaciers cover about 10% of the earth's surface today, but approximately 30% during the peak of the last Ice Age.
What are type of Glaciers ?
Alpin (Valley)

Continental (Ice Sheet)
Alpin (Valley):
Form in and are restricted to, high gradient river valley in mountainous areas. Most common type in existence today.
What is know as movement of Glaciers ?
Basal Sliding

Plastic Flow
Basal Sliding
The glacier, as a single mass, slides over the underlying rock on a layer of meltwater.
Plastic Flow
The individual ice grains slide over each other. They also deform and recrystallize.
Rate of movement
Movement varies over the course of the year, but averages between 0.1 and 10 meter per day. Plastic flow is faster near the center.

Glaciers may temporarily move much faster, over 100 meters per day, by Surging. This is often caused by a build-up of meltwater beneath the ice which may float the glacier.
glacial budget
Ablation - The loos of glacial ice by melting, sublimation or calving (pieces falling off the end. )

The terminus of a glacier will advance if accumulation exceeds ablation. The terminus will retreat if ablation exceeds accumulation - But the glacial ice will still flow forward.

There is always a time lag if the budges changes
Ablation
The loos of glacial ice by melting, sublimation or calving (pieces falling off the end. )
What are two type of Glacial Erosion ?
Pulcking

Abrasion
Pluckin
Erosion combined with mechanical weathering. Ice fractures the underlying bedrock then freezes it to the glacier.
What are few Erosional Landforms ?
Cirques

Horns

Aretes
Cirques
(Point of origin of the valley. ) Steep-sided, amphitheater-shaped recesses carved into a mountain at the head of a glacial valley. Often later occupied by tarns - Bedrock-floored lakes.
Horns
Eroded peaks formed when three or more cirques cut back into a mountain.
Aretes
Eroded ridges between glacial valleys.
What are three River Sediment (Load)
Dissolved Load
Suspended Load
Bedload
Suspended Load
Fine sand, silt, and mud that are held in the water.
Dissolved Load
Chemically weathered materials
Bedload
Larger material that moves by rolling or sliding
What are three transportation of sediment ?
Competence
Capacity
Capacity
The total amount of sediment that a river is able to transport.
Sedimentation
River deposited sediment is collectively called Alluvium. It will collect wherever water velocity decreases within a river system:

In the channel - Sand bars, point bars
Along the banks - Levees
At the mouth - Deltas, alluvial fans
Alluvial Fans
The largest tend to form in deserts
Time and Topography
The appearance of the river valley and the dominant processes acting within it are affected by time and gradient.
Downcutting - Deepens valleys
Lateral Erosion - Widens Valleys
Headward Erosion - Lengthens valleys
Mass Wasting - Widens valleys
River Channels
High Gradient: Often far above base level (mountains)

Down cutting is dominant.

The channel is often narrow, straight and may contain rapids, and waterfalls.

V-Shaped canyons are common in these areas.
Moderate Gradient
Downcutting is no longer dominant. Lateral and headward erosion and mass wasting are all significant.

The channel is wider and shallower. Meanders, floodplains, and levees form.
Low Gradient
Elevations are often very close to base level. Downcurring is not significant, lateral erosion is dominant.

The channel is often very wide and shallow, with many meanders, oxbow lakes, large floodplains, and broad levees.
River Channels Features
If base level is lowered or land is uplifted, rivers adjust to the increased gradient by resuming downcutting

Incised meanders - meandering channels with steep-sided canyons and no floodplain

Terraces - Abandoned former floodplains.
Hydrology
Approximately 97% of the earth's water is located in the Oceans.

2% is frozen as glacial ice or sea ice.

<1% is found in rivers, lakes, groundwater.

And the atmosphere. Rivers are the dominant causes of erosion (transportation of material) on earth today.

(erosion goto to have some kind of transposition not just gravity.)
What are velocity of rivers (Runoff)
Gradient
Shape
Discharge
Amount of debris in the channel
Gradient (slope)
Velocity tends to be higher on steeper slopes.
Discharge (Volume of water over time)
Increasing discharge increases velocity.
Shape of the river channel
Semicircular-shape channels have less friction with water than narrow or shallow channels.
Amount of debris in the channel
Water flows faster in the absence of any type of impediment - Fallen trees, rocks, etc

This includes rapids. Water will move faster between the rocks in rapids, but the overall velocity of the river decreases.
Velocity
The area of highest velocity in a river channel varies as the channel's shape varies.

In a straight channel, its in the middle, about ¼ of the way to the bottom.

In a curving channel, its deflected to the outside of the bends. Erosion is, therefore, more concentrated there.
Longitudinal Profile
As a river flows from its source to its mouth:
Gradient Decreases
Discharge Increases

Amount of rapids decrease

The river becomes wider and shallower
Base Level
Rivers flatten out as they near their mouths. This is due to the combined forces of erosion (greatest near the mouth) and mass wasting.

A river cannot erode its channel much deeper than the elevation of the body of water that flows into. This is the river's base level
What are three type of Base Level
Ultimate Base Level
Local Base Level
Base Level
Ultimate Base Level
Sea level for most major rivers, but there are exceptions. The Jordan River's base level is The Date Sea.
Local Base Level
Lake, waterfalls, man-made reservoirs behind dams, other rivers, etc.
Base Level
When a river reaches its base level, velocity falls close to zero. As velocity falls, so does the river's capability to erode downward. This is why the river flattens out near their mouths.
Base level change example
Base level falls
Base Level rises
If the base level falls:
The river will resume downcutting and erode a deeper channel, possibly forming a canyon.
If the base level rises
The gradient is reduced, the river slows and begins to deposit sediment. The channel will build higher to reach the new base level.
Base Level Decreases due to
Lower Sea Level
Rising Land Elevations
Base Level Increases due to
Higher sea level
Lower land elevations
GroundWater
Approximately 0.6% of the earth's water supply 0- 14% of all freshwater and 94 percent of unfrozen freshwater

It can be found in soil, sediment and many different rock types. The properties of rock and sediment will determine if groundwater can accumulate.
Porosity
The percentage of void space in sediment and rock (mostly sedimentary)
What are 5 type of porosity
Particle Shape
Particle Size
Sorting
Packing
Cementation
Particle Shape -
Spherical particles generally have the greatest degree of empty space between them. Flat particles often stack more closely together.
Particle Size -
If all else is equal, size alone won't affect porosity. However, larger grains often lead to lower porosity
Sorting -
Well sorted material has much higher porosity than poorly sorted material.
Packing -
A greater degree of packing will lower porosity. Seen mainly in sediment.
Cementation
Cementation (or high mud content ) lowers porosity substantially. Graywacke has less porosity than quartz sandstone.
Permeability
The ability to transmit a fluid (water). This requires that the pores interconnect.

Pumice has porosity, but little permeability.

Clay and shale have porosity, but the pores are very small and poorly connected. Most igneous and metamorphic rocks have little permeability.

Gravel -->Sand---->Silt-------->Clay
Fast ----------------------------->>Slow (water goes through)
Porosity and Permeability
Material with both high porosity and high permeability are aquifers (most sediment and sedimentary rocks.) The water table is the top of the groundwater layer within near surface aquifers.

Materials with low permeability are Aquitards (shale and most igneous/metamorphic rocks).
Aquifers
When aquifers have a direct connection to the surface, they are UNCONFINED. They are recharged directly by rainfall and/or snowmelt.

Aquifers located below an aquitard layer are confined. They recharge with water slowly, but it is often cleaner due to filtration through the aquitard.
Geysers -
exist where groundwater is superheated by magam. When pressure builds, the groundwater erupts.
Hot Springs -
Are heated to a smaller degree and don't erupt.
Groundwater Erosion Effictivness
Based not on velocity, but no the effectiveness of chemical weathering. This will affect rocks such as limestones, dolostones and rock gypsum much more than sandstones, shales, etc.

Erosion is further aided by preexisting fractures (faults and joints) and precedes most rapidly at or near the water table.
What are erosional landforms?
Fjords, Striation and Grooves, Roches mountonness. Cracks, cave, arch, stack, stump,
Fjords
Flooded glacial valleys that form from post-glacial sea level rise or sub-base level erosion.
Striations and Grooves
Scratches in bedrock from mm to meters in width and depth. Used to interpret the direction of former ice movement. Kelleys island has well-preserved grooves.
Roches Mountonnees
Eroded hills of bedrock that were resistant to glacial erosion. They are usually elongated and streamlined. The gentle side of the hill faces into the direction from which the ice came, the steeper side faces in the direction of ice movement.
Depositional landforms Glacial Sediment
Till and Outwash
Till
Material Deposited directly by glacial ice. It is unsorted and unstratified mud, sand, gravel and boulders.
Outwash
Material laid down or reworked by meltwater. Sorted and stratified and sand and gravel.
Landforms made of till
Glacial erratics

Drumlines
Glacial erratics
Boulders derived from non-local bedrock.
Drumlines
oval or elongated hill believed to have been formed by the streamlined movement of glacial ice sheets across rock debris, or till
Moraines
End moraine - A ridge piled up along the front edge of glacier.
Terminal
Recessional
Terminal
The last moraine, marks the greatest extent of the glaciers.
Recessional
Forms as a glacier retreats.
Other Moraines
Lateral Moraine- forms along the sides of many valley glaciers.
Medial Moraine - A dark streak marking the union of two lateral moraines.
Ground Moraine - Relatively thin blanket of till left behind as a glacier retreats.
Landform made of Outwash
Outwash plain = Thick blanket of sand and gravel
Eskers = Long, sinuous ridges that form in subglacial stream channels.
Kames = irregular, mound-like hills
Kettles = Shallow depressions marking the location of old, buried ice blocks that melted. These are often later filled with water and become kettle Lakes.

Kettle lakes are floored by sediment.

Trans are floored by bedrock.
Deserts
Deserts are areas that receive very little rainfall (<25 cm/yr) or the equivalent in snowfall.

Not all deserts are hot, Antarctica is a desert.

Mechanical and chemical weathering are reduced, so soil formation is limited. Mass wasting and erosion are also slowed due to lowered amounts of surface water.
What creates deserts and what type of deserts are they ?
Rainshadow effect
Mid-Continental effect
Coldwater effect (Coastal deserts)
Geographic Effect
. Rainshadow effect (topographic deserts):
A consistently high elevation mountain range may block significant rainfall from reaching downwind locations.
Mid-Continental effect
Regions far from water receive less rain. The Shara and Gobi Deserts
Coldwater effect (Coastal deserts)
Areas near perpetually cold ocean water often have very low humidity.
Geographic Effect
At 30 latitude (both north and south) and at the poles, areas of regional high pressure exist. High pressure tends to discourage cloud formation - thus rainfall is less likely

The Sahara, Kalahari, Arabian, Australian, Sonoran Deserts,
Deserts Topography
Water plays the most significant role, even if somewhat infrequently, in the formation of desert landforms.

Intermittent streams flow from the highlands into playa lakes. Alluvial fans form at the mouths of these streams and merge together to form Bajadas.
If there are mountains in the area, they eventually erode flat and form
Desert Erosion
Water is the major erosional force in most deserts, occurring sporadically during flash floods.

Wind, although far less powerful, is responsible for the day-to-day erosional activity. Wind moves and sorts sand and silt -- Gravel is too heavy, and clay is held too firmly to electrostatic charges.
Wind Erosion
Deflation
Abrasion
Deflation
Small, loose material is removed, leaving larger gravel behind. This gravel becomes concentrated into Desert Pavement.
In areas with little or no gravel, the land surface continues to decrease in elevation forming a blowout.
Abrasion
Airborne material "sandblasts" rocks forming ventifacts - rocks eroded flat on one or more surfaces.
Slow chemical weathering may form desert varnish - a dark surface sometimes seen on stable desert rocks.
Wind Deposition
Wind deposited silt becomes loess.
Often found far downwind of deserts or areas of glacial sediment.

Wind Deposited sand becomes dunes.
Most dunes migrate and have internal structure - Cross bedding and ripple marks.
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