Asbog 5

traction

Movement by rolling, sliding, or dragging of sediment fragments along a stream bottom.

trellis pattern

A drainage pattern consisting of parallel main streams with short tributaries meeting them at right angles. (End Chapter 10)

Aquifer

A body of saturated rock or sediment through which water can move readily. (Begin Chapter 11)

artesian well

A well in which water rises above the aquifer.

concretion

Hard, rounded mass that develops when a considerable amount of cementing material precipitates locally in a rock, often around an organic nucleus.

cone of depression

A depression of the water table formed around a well when water is pumped out; it is shaped like an inverted cone.

confined (artesian) aquifer

An aquifer completely filled with pressurized water and separated from the land surface by a relatively impermeable confining bed, such as shale.

drawdown

The lowering of the water table near a pumped well.

gaining stream

A stream that receives water from the zone of saturation.

geode

Partly hollow, globelike body found in limestone or other cavernous rock.

geyser

A type of hot spring that periodically erupts hot water and steam.

ground water

The water that lies beneath the ground surface, filling the cracks, crevices, and pore space of rocks.

hot spring

An area of volcanic eruptions and high heat flow above a rising mantle plume.

karst topography

An area with many sinkholes and a cave system beneath the land surface and usually lacking a surface stream.

losing stream

Stream that loses water to the zone of saturation.

perched water table

A water table separated from the main water table beneath it by a zone that is not saturated.

permeability

The capacity of a rock to transmit a fluid such as water or petroleum.

petrified wood

A material that forms as the organic matter of buried wood is either filled in or replaced by inorganic silica carried in by ground water.

porosity

The percentage of a rock's volume that is taken up by openings.

saturated zone

A subsurface zone in which all rock openings are filled with water.

sinkhole

A closed depression found on land surfaces underlain by limestone.

speleothem

Dripstone deposit of calcite that precipitate from dripping water in caves.

spring

A place where water flows naturally out of rock onto the land surface.

stalactite

Iciclelike pendant of dripstone formed on cave ceilings.

stalagmite

Cone-shaped mass of dripstone formed on cave floors, generally directly below a stalactite.

unconfined aquifer

A partially filled aquifer exposed to the land surface and marked by a rising and falling water table.

vadose zone

A subsurface zone in which rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone.

water table

The upper surface of the zone of saturation.

well

A hole, generally cylindrical and usually walled or lined with pipe, that is dug or drilled into the ground to penetrate an aquifer below the zone of saturation. (End Chapter 11)

Ablation

The loss of the glacial ice or snow by melting, evaporation, or breaking off into icebergs. (Also called wastage). (Begin Chapter 12)

advancing glacier

Glacier with a positive budget, so that accumulation results in the lower edges being pushed outward and downward.

alpine glaciation

Glaciation of a mountainous area.

arête

A sharp ridge that separates adjacent glacially carved valleys.

basal sliding

Movement in which the entire glacier slides along as a single body on its base over the underlying rock.

cirque

A steep-sided, amphitheater-like hollow carved into a mountain at the head of a glacial valley.

continental glaciation

The covering of a large region of a continent by a sheet of glacial ice.

crevasse

Open fissure in a glacier.

drumlin

A long, streamlined hill made of till.

end moraine

A ridge of till piled up along the front edge of a glacier.

equilibrium line

An irregular line marking the highest level to which the winter snow cover on a glacier is lost during a melt season. (Also called snow line.)

erratic

An ice-transported boulder that does not derive from bedrock near its present site.

esker

A long, sinuous ridge of sediment deposited by glacial meltwater.

fjord

A coastal inlet that is a glacially carved valley, the base of which is submerged.

glacier

A large, long-lasting mass of ice, formed on land by the compaction and recrystallization of snow, which moves because of its own weight.

ground moraine

A blanket of till deposited by a glacier or released as glacier ice melted.

hanging valley

A smaller valley that terminates abruptly high above a main valley.

horn

A sharp peak formed where cirques cut back into a mountain on several sides.

iceberg

Block of glacier-derived ice floating in water.

ice cap

A glacier covering a relatively small area of land but not restricted to a valley.

ice sheet

A glacier covering a large area (more than 50,000 square kilometers) of land.

kettle

A depression caused by the melting of a stagnant block of ice that was surrounded by sediment.

lateral moraine

A low ridgelike pile of till along the side of a glacier.

moraine

A body of till either being carried on a glacier or left behind after a glacier has receded.

outwash

Material deposited by debris-laden meltwater from a glacier.

plastic flow

Movement within a glacier in which the ice is not fractured.

pluvial lake

A lake formed during an earlier time of abundant rainfall.

receding glacier

A glacier with a negative budget, which causes the glacier to grow smaller as its edges melt back.

rigid zone

Upper part of a glacier in which there is no plastic flow.

rock-basin lake (tarn)

A lake occupying a depression caused by glacial erosion of bedrock.

rock flour

A powder of fine fragments of rock produced by glacial abrasion.

tarns

See rock-basin lake.

terminus

The lower edge of a glacier.

theory of glacial ages

At times in the past, colder climates prevailed during which significantly more of the land surface of Earth was glaciated than at present.

till

Unsorted and unlayered rock debris carried by a glacier.

tillite

Lithified till.

truncated spur

Triangular facet where the lower end of a ridge has been eroded by glacial ice.

U-shaped valley

Characteristic cross-profile of a valley carved by glacial erosion.

valley glacier

A glacier confined to a valley. The ice flows from a higher to a lower elevation.

varve

Two thin layers of sediment, one dark and the other light in color, representing one year's deposition in a lake.

zone of ablation

That portion of a glacier in which ice is lost.

zone of accumulation

That portion of a glacier with a perennial snow cover. (End of Chapter 12)

Bajada

A broad, gently sloping, depositional surface formed at the base of a mountain range in a dry region by the coalescing of individual alluvial fans. (Begin Chapter 13)

barchan

A crescent-shaped dune with the horns of the crescent pointing downwind.

blowout

A depression on the land surface caused by wind erosion.

butte

A narrow pinnacle of resistant rock with a flat top and very steep sides.

deflation

The removal of clay, silt, and sand particles from the land surface by wind.

desert

A region with low precipitation (usually defined as less than 25 cm per year).

fault

A fracture in bedrock along which movement has taken place.

flash flood

Flood of very high discharge and short duration; sudden and local in extent.

loess

A fine-grained deposit of wind-blown dust.

longitudinal dune (seif)

Large, symmetrical ridge of sand parallel to the wind direction.

mesa

A broad, flat-topped hill bounded by cliffs and capped with a resistant rock layer.

parabolic dune

A deeply curved dune in a region of abundant sand. The horns point upwind and are often anchored by vegetation.

pediment

A gently sloping erosional surface cut into the solid rock of a mountain range in a dry region; usually covered with a thin veneer of gravel.

plateau

Broad, flat-topped area elevated above the surrounding land and bounded, at least in part, by cliffs.

playa

A very flat surface underlain by hard, mud-cracked clay.

playa lake

A shallow temporary lake (following a rainstorm) on a flat valley floor in a dry region.

rain shadow

A region on the downwind side of mountains that has little or no rain because of the loss of moisture on the upwind side of the mountains.

sand dune

A mound of loose sand grains heaped up by the wind.

slip face

The steep, downwind slope of a dune; formed from loose, cascading sand that generally keeps the slope at the angle of repose (about 34°).

transverse dune

A relatively straight, elongate dune oriented perpendicular to the wind.

ventifact

Boulder, cobble, or pebble with flat surfaces caused by the abrasion of wind-blown sand. (End Chapter 13)

arch (sea arch)

Bridge of rock left above an opening eroded in a headland by waves. (Begin Chapter 14)

barrier island

Ridge of sand paralleling the shoreline and extending above sea level.

baymouth bar

A ridge of sediment that cuts a bay off from the ocean.

beach

Strip of sediment, usually sand but sometimes pebbles, boulders, or mud, that extends from the low-water line inland to a cliff or zone of permanent vegetation.

beach face

The section of the beach exposed to wave action.

berm

Platform of wave-deposited sediment that is flat or slopes slightly landward.

breaker

A wave that has become so steep that the crest of the wave topples forward, moving faster than the main body of the wave.

coast

The land near the sea, including the beach and a strip of land inland from the beach.