Geology Test 3 Study Guide

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Alluvial Fan

Large sediment deposit formed when material eroded from a mountainous canyon is transported to a plain, often by a flash flood

Saltation

Mode of sediment transport in which sediment (usually sand) jumps or bounces

Delta

Large sediment deposit formed when a river empties into a larger body of water (often the ocean) and loses its channel

Discharge

Volume of water flowing in a stream at a specific time and location

Bedload

Total amount of larger sediment carried by a stream that is in contact with the ground below the stream as it moves

Meander

Sinuous curve in a section of a mature stream

Levee

Stream bank that has increased in height by natural or human means

Flood Plain

Low-relief area adjacent to a stream channel where water and sediment are carried when the volume of water is too much for the channel to hold

Drainage Basin

Land area in which water feeds into a particular stream system

Point Bar

Sediment deposit on the inside of a meander, formed as a result of lower velocity in that section of a stream

Suspended Load

Total amount of lighter sediment that a stream can carry easily in the water

Distributary

Smaller stream that branches off from a larger stream, usually close to the mouth

Cut Bank

The outside edge of a meander, which experiences erosion due to fast-moving water

Trellis

Drainage pattern in which stream channels follow topographic features and valleys formed from the differential weathering folded rocks

Channelization

Attempt to reduce flooding by changing the natural path of a stream, often straightening it

Rectangular

Drainage pattern in which stream channels have 90-degree turns because they follow joints and faults

Oxbow Lake

An older meander of a stream that was cut off when a straighter channel formed

Recurrence Interval

Average time between a flooding event of a particular size, based on statistical analysis of historical events

Braided Stream

Formed when a stream has a high sediment load and a varying discharge

Pothole

Smooth, steep-walled depression that forms in a bedrock streambed by the abrasion of sediment

Dendritic

Tree-like drainage pattern in which multiple tributaries feed into one large stream

Abrasion

Form of stream erosion resulting from sediment collisions

Base Level

The lowest elevation to which a stream can erode

Retention Pond

Man-made water-collecting basin created in an attempt to reduce flooding by capturing run-off

Stream

Channelized water under the influence of gravity

Dissolved Load

Total amount of chemical sediment carried by a stream in the form of ions

Radial

Drainage pattern in which multiple tributaries flow outward from a central high point

Tributary

A smaller stream that flows into and contributes to a larger stream

Hydraulic Action

Form of stream erosion resulting from the force of moving water alone

Sheetwash

Water under the influence of gravity, but not channelized

Placer

Deposit of denser material in a slow-moving or protected part of a stream

Divide

Topographical feature that separates one drainage basin from another

Traction

Mode of sediment transport in which sediment remains in contact with the bottom of a stream as it slides or rolls in the direction of the current

Artesian Well

A well tapping a confined aquifer, in which water rises above the level of the aquifer due to pressure

Recharge

Any area or process in which water is added to groundwater

Cone of Depression

Localized drawdown of a water table due to heavy pumping from a well

Sinkhole

Topographic depression that occurs when underlying soluble rock features cannot support the land above them

Permeability

Ability of water or other fluids to move through a material

Porosity

Percent of available space in a rock, sediment, or soil, which may be saturated by water

Karst

Rock and landscape features that form in locations with soluble rock (e.g. caves)

Losing Stream

When water flows out of a stream into groundwater

Saltwater Intrusion

Contamination of a freshwater aquifer by seawater, resulting from heavy pumping of an aquifer in a coastal region

Unconfined Aquifer

A water-saturated and permeable material without an impermeable layer above it

Spring

Location where groundwater is forced to the surface due to underground geologic features

Perched Water Table

Upper boundary of a small aquifer that is shallower than the main water table in an area

Confined Aquifer

A water-saturated and permeable material capped by an aquitard

Discharge

Any area or process in which water is removed from groundwater

Aquitard

Shale is an example of this feature, in which low permeability drastically slows the flow of water

Water Table

Boundary that separates saturated and unsaturated material in an unconfined aquifer and fluctuates in depth

Varve

Sediment bed formed in glacial lakes that has thin, parallel layers alternating in texture, showing annual cycles in the amount of glacial meltwater

Recessional Moraine

Ridge-like accumulation of glacial sediment deposited at the end of a glacier during a pause in its retreat

Equilibrium Line

Boundary between the Zone of Accumulation and Zone of Ablation in a glacier

Horn

Sharp peak formed from three or more cirques around a central location

Kame

Hill or mound of stratified drift that was originally deposited in a lake on a glacier’s surface

Firn

Intermediate material between snow and glacial ice, formed from snow compaction

Erratic

A rock transported by a glacier and deposited at a location that is comprised of different material than it is

Tarn

A glacial lake that forms in a cirque

Till

Poorly sorted sediment deposited directly by glacial ice

Iceberg

Mass of free-floating ice that has calved from a glacier

Plucking

Process in which meltwater at the base of a glacier gets into cracks and then refreezes, picking up pieces of bedrock that the glacier then carries

Ice Shelf

Section of an ice sheet that flowed out into the ocean, and rests on top of water

Lateral Moraine

Ridge of glacial sediment scraped off by an Alpine glacier and deposited on the edges of its valley

Ice Sheet

Found only in Greenland and Antarctica today

Terminal Moraine

Ridge-like accumulation of till that marks the farthest extent of a glacier

Drumlin

Asymmetric till hill that indicates the direction a continental ice sheet traveled

Hanging Valley

A glacially carved tributary valley perched above a larger glacier valley, causing a steep cliff to form

Pater Noster Lakes

String of rock basins in u-shaped valleys that fill with water after glaciers are gone

Glacier

Large accumulation of moving ice formed when more snow accumulates than melts over long time periods

Medial Moraine

Accumulation of glacial sediment formed where two alpine glaciers join together

Ground Moraine

Glacial debris strewn across a land surface by glacial movement

Fjord

Narrow, steep-sided glacial valley flooded by rising sea level

Kettle

Depression formed when a large piece of ice left by a retreating glacier is buried in sediment and later melts, causing the ground to subside

Outwash Plain

Land area in which glacial sediment is deposited at the end of a glacier by the runoff of glacial meltwater

Calving

The sudden release of an ice mass into water from the end of a glacier

Stratified Drift

Sorted sediment deposited by meltwater from a glacier

U-Shaped Valley

Valley with near-vertical sides carved by a glacier

Sea Ice

Frozen seawater that floats on the surface of the ocean, such as in the Arctic, and is sensitive to changes in temperature

Rock Flour

Fine sediment ground up by a glacier

Glacial Rebound

Isostatic adjustment where Earth’s crust uplifts after a glacier retreats

Cirque

Amphitheater-shaped basin with steep walls formed by mass wasting and heavy snow accumulation at the head of an Alpine glacier

Esker

Sinuous mound of sediment originally deposited by a stream underneath a glacier

Crevasse

Large fissure found in the brittle upper 40-50 meters of a glacier

Arête

A sharp-crested ridge that forms as a divide between two glaciers

Playa

Flat valley found in places such as the Basin and Range, with fine-grained sediment, evaporates, and occasional short-lived lakes

Hogback

Sharp ridge of resistant tilted rock layers formed as a result of differential weathering

Loess

Wind-blown angular silt and clay (may include rock flour)

Longitudinal Dune

Very long, straight, symmetric dune formed parallel to the wind direction in places with abundant sand

Ventifact

Rock with surfaces shaped by the abrasion of saltating sand

Crossbeds

Sedimentary structure formed by stacking of slip faces as a dune migrates

Bajada

Large sediment deposit where multiple alluvial fans have merged at the base of a mountain range

Butte

Smallest classification of a flat-topped topographic feature capped by resistant rock

Parabolic Dune

Curved dune with horns that point upwind, usually because they are anchored by vegetation

Desertification

Process by which human activity causes regions to become more desert-like

Slip Face

The downwind side of a dune, with its slope equal to the angle of repose

Blowout

Depression on the land surface caused by wind erosion

Badlands

Topography that results from eroded shale in dry environments

Deflation

Process by which lighter material is eroded by wind, lowering the ground surface; for example, when dry sand is removed to the level of the water table

Transverse Dune

A rough linear dune that forms perpendicular to the wind direction

Plateau

Largest classification of a flat-topped topographic feature capped by resistant rock

Mesa

Middling classification of a flat-topped topographic feature capped by resistant rock