CUMULATIVE ERTH 209 Final Terms

Mass Wasting

The down-slope movement of earth materials under the influence of gravity.

1. Gravity

2. Slope shear strength

Gravity and Shear Resistance (Inclined Plane)

Shear Strength

The relationship between shear and normal force in a block of material on a slope. When shear force is greater than normal force, mass wasting can occur.

Cohesion

The ability of a material to stick together

Angle of Repose

The slope angle where shear forces and normal forces are equal. The most stable point for rock and soil material

Slope Stability

Determined by:

1. Angle of the slope

2. Shear strength of the accumulated materials

Water and Pore Space

If water is added to pores, the angle of repose will increase. If too much is added, the water decreases the shear strength/lowers the angle of repose.

Mass Wasting Events

1. Earthquakes

2. Over-Steepening Slope

3. Vegetation Removal

4. Water Introduction

5. Ice Wedging

6. Biologic Activity

Mass Wasting Events Classification

1. Rate of Movement

2. Type of Material

3. Nature of Movement

Creep

The imperceptibly slow downward movement of material caused by a regular cycle of nighttime freezing followed by daytime thawing in unconsolidated material, such as soil.

Solifluction

The slow movement of soil lobes on low-angle slopes due to soil seasonally freezing and thawing in high-latitude.

Debris Flow

A mixture of coarse material and water, channeled and flowing downhill rapidly.

Earthflows

A mixture of fine material and water, channeled and flowing downhill rapidly if water added..

Lahars/Mudflows

A type of volcanic mudslide, in which rain or snowmelt accumulates volcanic ash of the slopes of steep volcanoes or other mountains and then wash downhill, causing damaging flooding.

Slides

An intact, cohesive mass travelling on a well-defined surface as a result of gravity.

• tilted plane

  • bedding planes

  • foliation

• triggers

  • earthquakes

  • introduction of water

Slumps

• gravity > slope strength

• cohesive mass

• base of slope removed

• curved slip surface

• triggers

  • undercutting

  • earthquakes

  • introduction of water

Rock Falls

• fast movement

• steep slopes

• creates a talus slope

• triggers:

  • earthquakes

  • freeze-thaw cycles

  • animals

Rock Avalanches

• fast

• steep slopes

• rock explodes at bottom

• triggers

  • earthquakes

  • freeze-thaw cycles

Minimizing Slope Hazard

Shielding, catching, and diverting the runout material through fencing, runout channels, diversion structures, and check dams.

Hydrologic Cycle Steps

1. Evaporation

2. Transpiration

3. Condensation

4. Precipitation

5. Infiltration

6. Runoff

Stream

A channeled body of water.

Floodplains

The low-lying, nearly flat alluvial valley floor that is periodically inundated with flood waters.

Stream Velocity

The distance water travels in a stream over a measured time period.

Slow = <1 km/h

Fast = 5 km/h

Flood = 25 km/h

Channel Shape

The greater the cross-sectional area is compared to the wetted perimeter, the greater the velocity, because less of the water is experiences friction.

Gradient

Vertical Drop

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Horizontal Distance

Channel Roughness

The rougher the channel is, the slower the flow.

Thalweg

A line marking the fastest moving water in a channel.

Discharge

The total volume of water flowing past a point at a given time.

Q = Depth x Width x Velocity

Stream Erosion

1. Hydraulic Action- Force of water

2. Solution- chemical erosion

3. Abrasion- particle erosion

Hydrologic Force

Solution

The act of taking a solid and dissolving it into a liquid. Commonly occurs with salts/other minerals in water.

Abrasion

Stream Sediments

Pieces of rock found in streams that have been weathered and possibly eroded.

Bedload

Sediment that is large and dense, typically sits on the bottom of stream channels, and is only moved with higher-speed flows.

Suspended Load

Smaller particles that are picked up by flowing water and carried in suspension above the bedload.

Dissolved Load

The total amount of ions in solution from chemical weathering. Amount not affected by flow velocity.

Flooding Cause

Heavy rain, rapid snow/ice melting, geography (low-lying areas).

Floodplain Formation

The low-lying area of land adjacent to a river or stream which commonly experiences floods.

Natural Levee Formation

Built-up area around a river channel which can hold river flow within a channel. Forms from repeated flooding, which builds up ‘walls’ around the edge of the river.

Discharge and Flooding Events

Increased discharge = Increased energy/erosion/transportation

Flood Recurrence Interval

The average number of years between peak discharge values of a certain size. Helps determine how frequently a stream overflows its banks/floods.

Stream Evolution

Base Level

The elevation of the mouth of the river. The lowest level to which a stream can erode.

Ultimate Base Level

Sea level.

Local Base Level

Temporary obstructions to down-cutting encountered by a stream. Ex. Resistant rock beds, waterfalls, lakes, artificial dams.

Vertical Erosion

The deepening of a channel of a stream of valley by removing material from the stream bed or the valley flow. Depends on the base level.

Lateral Erosion

Side-to-side erosion in which channel location migrates with time. Erosion on outside bend, deposition on inside bend.

Groundwater

Freshwater stored in the pore spaces of rock beneath the surface of the earth, supplies water to streams.

Zone of Aeration

Place where pores are filled with some water and some air, above the water table.

Zone of Saturation

The area beneath the earth’s surface where all available voids in the soil and rock are completely filled with water.

Water Table

The part of the groundwater system which has pore space 100% filled with water.

Dry Water Table

The part of the water table that dries up in certain seasons (?)

Wet Water Table

The part of the water table that stays wet no matter the season (?).

Unconfined Aquifers

The water table that follows the general shape of the topography. Water flows down gradient.

Confined Aquifers

The water table between two impermeable layers (aquitards). Water flows down gradient. Has a recharge zone.

Perched Aquifers

Minor table above the main water table. Aquitard prevents flow to main table. Water flows laterally.

Porosity

The total volume of void space in a rock. Depends on sediment size & shape, grain packing, degree of sorting & cementation.

High Porosity Rocks

Shales made of clays have poorly connected pores, and therefore low permeability.

Permeability

The interconnectedness of the pore spaces which allows water movement.

High Permeability Rocks

High internal water flow.

Low Permeability Rocks

Low or no internal water flow.

Aquifer

The permeable layer that transmits water. High porosity and permeability.

Aquitard

A layer with lower porosity and/or permeability which allows only minimal and/or slow fluid flow.

Darcy’s Law

The law which calculates velocity proportional to the slope.

Flow varies with porosity (n) and permeability (K).

Represents total water flowing through an aquifer at a given time (m³/day).

Henry Darcy

A French engineer who developed a hypothesis in 1956 to show how discharge through a porous medium is controlled by permeability, pressure, and cross-sectional area.

Artesian Well

The event which happens when groundwater rises above the top of the water table. Confined aquifer.

Natural Springs

Where confined and perched water tables meet.

Drawdown

The lowering of the surface elevation of a body of water/the water table/the water surface as a result of the withdrawal of water.

Depletion

The extraction of water from an aquifer at a rate greater than that of natural recharge.

Subsidence

The act of land surface down-warping, typically referred to when discussing sedimentation or with rapid groundwater removal.

Contamination

Pollutants dissolved into the ground/water sources which then carry them to places where they infiltrate and become part of the groundwater.

• Non-/Point sources

Karst Topography

An irregular, hilly terrain characterized by sinkholes, caves and a lack of surface streams created by groundwater dissolving limestone.

Cave and Cavern Formation

As the water continues to dissolve its way through the limestone, it can leave behind intricate networks of caves and narrow passages.

Depositional Features:

• stalactites

• stalagmites

• columns

• flowstone

Chemical Weathering (Karst)

Breaking down of mineral material via chemical methods, like dissolution and oxidation.

Limestone

• Chemical sedimentary rock

• Calcite (CaCO₃)

• Susceptible to chemical weathering

• 10% of Earth’s surface

Sinkholes

Small, steep depressions in land surfaces.

Three types:

1. Dissolution

2. Cover-subsidence

3. Cover-collapse

Formed by two processes:

• Dissolution

• Suffosion

Glaciers

A large mass of ice that formed from the accumulation of snow and flows slowly downslope. Forms from the accumulation, compaction, and recrystallization of snow.

U-Shaped Glacial Troughs

Broad, U-shaped valley cut by main glacier.

Hanging Valleys

U-shaped valley standing above glacial trough, formed by tributary glacier. Can be associated with waterfalls.

Cirque Glacier

Bowel-shaped depression formed at head of valley glacier.

Arete

A knife-edged ridge that is carved between two glacial valleys (cirques).

Horn

Sharp, pyramid-shaped peaks formed between cirques.

Depositional Landforms

Landforms created through the deposition of sediment.

Ground Moraine

Moraine that forms beneath a glacier. Deposited as glacier retreats.

End Moraine

Moraine that forms at the end of a glacier.

Lateral and Medial Moraines

The ridges of glacial till formed on the sides of a valley/between two merging glaciers.

Drumlins

Streamlined asymmetrical hills formed when a glacier moves a previously deposited glacial till. 15-60 meters tall, 0.4 - 0.8 km long.

Kame

Steep-sided cone of glacial till comprised of sand and gravels. Formed at the end of a glacier.

Kettle

Depression formed by melting ice stored in a moraine. Empty or filled with water. Less than 2km in diameter, avg depth 10m.

Esker

Sinuous ridge formed by a stream moving below glacier. Formed by sand and gravels, standing several meters tall.

Zone of Accumulation

The zone where snow and ice are added to a glacier.

Zone of Ablation

The zone in which snow and ice melts on a glacier.

Snowline

The line between the zone of accumulation and the zone of ablation.

Pressure Melting (Basal Sliding)

The act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant.

Glacial Advancing

Periods when glaciers grow and move forward. Mountain glacier’s terminus extends farther down valley than before.

Glacial Retreat

The process of a glacier shrinking or receding in size over time. Leaves boulders and masses of scraped-together rock debris and soil.

Moraine

A ridge of glacial till which is deposited when ablation is equivalent to accumulation.

Pleistocene Glaciation

Occurred between 1.7 mya to 10,000 ya in:

1. Nebraska

2. Kansas

3. Illinois

4. Wisconsin

Geographic Extent and Timing

Wisconsin Glaciation