GLG 110 final

groundwater

water found in the pores of soil and sediment, plus narrow fractures in bedrock

zone of soil moisture

a zone in which water is held by molecular attraction on soil particles in the near-surface zone; used by plants and evaporates directly back to the atmosphere

zone of saturation

a zone in which all of the pore spaces are completely filled with water

water table

the upper limit of the zone of saturation

the unsaturated zone

the area above the zone of saturation; pore spaces include both air and water

capillary fringe

a region where groundwater is held in pore spaces by surface tension; found in the unsaturated zone

gaining streams

gain water from the inflow of groundwater through the streambed; water table is higher than the stream surface

losing stream

lose water to the groundwater system by outflow through the streambed; water table is lower than the stream surface

combination streams

a stream can gain in some sections and lose in others

porosity

the percentage of pore (open) spaces in a rock or sediment; poorly sorted sediments have low porosity

permeability

the ability of a material to transmit a fluid; depends on the connectivity between pores

aquitard

an impermeable layer that hinders or prevents water movement (clay, mud, shale)

aquifer

permeable rock strata or sediment that transmits groundwater freely (sand, gravel)

groundwater movement

groundwater moves very slow, average rate is 4 centimeters per day; force of gravity and pressure differences moves groundwater

recharge area

how groundwater is replenished

discharge area

how groundwater flows back to the surface

Darcy's law

a measure of the volume of water that flows through an aquifer, using the hydraulic gradient, conductivity, and cross-sectional area

regional groundwater systems

interact with deeper, larger groundwater systems

wells

a hole bored into the zone of saturation; most common method of removing groundwater

drawdown

as water is withdrawn from the well, the surrounding water table is lowered

a cone of depression

a cone-shaped depression in the water table forms around a well

artesian well or spring

a system in which groundwater under pressure rises above the level of aquifer

aquitards

must exist above and below the aquifer to confine the aquifer; known as a confined aquifer

nonflowing artesian well

pressure surface is below ground level

flowing artesian well

pressure surface is above ground level

confined aquifer

one open on top to the effects of the atmosphere and land surface

springs

occur where the water table intersects earth's surface; natural outflow of groundwater

perched water table

can be caused by an aquitard creating a localized zone of saturation

hot springs

6 degrees Celsius to 9 degrees Celsius warmer than the mean annual temperature of the locality; heated by the cooling of igneous rock

geysers

intermittent hot springs in which columns of water erupt with force

how geysers work

occur where extensive underground chambers exist within hot igneous rock; groundwater heats, expands, changes to steam, and erupts

geyser deposits

chemical sedimentary rock accumulates at the surface; type of rock reflects the chemical makeup of the bedrock

mining groundwater

treating groundwater as a nonrenewable resource; in many places, the water available to recharge the aquifer is significantly short of the amount being withdrawn

subsidence

the ground sinks when water is pumped from wells faster than natural recharge processes can replace it

saltwater contamination

excessive groundwater withdrawal causes saltwater to be drawn into wells, thus contaminating the freshwater supply

sewage

extremely permeable aquifers (coarse gravel) have such large openings that groundwater may travel long distances without being cleaned

caverns

created by acidic groundwater dissolving soluble rock

travertine

calcium carbonate deposited as dripping water evaporates

speleothems

general name for all dripstone features

stalactites

hanging from the ceiling

stalagmites

form on the floor of a cavern

karst topography

a landscape that has been shaped mainly by the dissolving power of groundwater

sinkholes

formed by groundwater slowly dissolving the bedrock often accompanied by collapse

glacier

a thick mass of ice that forms over hundreds and thousands of years by the accumulation, compaction, and recrystallization of snow

hydrologic cycle

water can be trapped in a glacier for many years

valley glaciers

glaciers that exist in valleys of mountainous areas; flow down the valley

ice sheets

exist on a larger scale than valley glaciers; Greenland and Antarctica

ice age ice sheets

over the past 2.6 million years, ice sheets have advanced and retreated multiple times; 18,000 years ago, ice sheets covered large portions of North America, Europe, and Siberia

The Arctic Ocean

covered with sea ice (frozen seawater), not glacier ice; sea ice is up to 4 meters thick, whereas glacier are hundreds to thousands of meters thick

ice shelves

glacial ice flows into the sea; in shallow water, the ice touched bottoms and is grounded but in deep water, the ice shelf floats

firn

snow is recrystallized into a much denser mass of small grains

flow

how glacial ice moves; fastest in the center of the glacier

zone of fracture

the upper 50 meters of a glacier is brittle

crevasses

cracks in the ice are present in the zone of fracture but sealed off by plastic flow at depth

surges

extremely rapid movements in some glaciers

zone of accumulation

the area where a glacier forms; located above the snowline

zone of wastage

the area where there is a net loss of glacial ice

calving

the breaking off of large pieces of ice

glacial budget

the balance, or lack of balance, between accumulation and loss of ice

ablation

loss of ice is at the lower end of the glacier

abrasion

the process in which rocks in the glacier act like sandpaper to smooth and polish a rock surface

glacial erosion is controlled by:

rate of movement, thickness of the ice, types of fragments trapped in the ice, and the erodibility of the surface below the glacier

U-shaped glacial troughs

glaciers widen and deepen valleys

truncated spurs

glaciers tend to straighten valleys, removing sharp curves

hanging valleys

glaciers in a main valley typically erode more than tributary glaciers

a col

a gap created when two glaciers exist on opposite sides of a mountain and the dividing ridge erodes away

a cirque

a bowl-shaped depression that is typically found at the head of a glacial valley

an arete

a sharp-edged ridge

a horn

a pyramid-like peak

fjords

deep, steep-sided inlets; drowned glacial thoughts that form when sea level rises

roches moutonnees

An asymmetrical knob of bedrock produced by continued glacial erosion

glacial deposits

as glaciers melt, rocks and sediments in the glaciers are deposited

glacial drift

refers to all sediments of glacial origin

till

material that is deposited directly by the ice

stratified drift

sediment laid down by glacial meltwater

a moraine

a landform made of glacial till

lateral moraine

an accumulation of debris on the side of the glacial till

medical moraine

created when two alpine glaciers converge; each glacier converges in the center of a new glacier

end moraine

an accumulation of debris that forms at the terminus of a glacier

ground moraine

a rock-strewn plain created as the glacier retreats

drumlins

smooth, elongate parallel hills composed of till and formed from ice sheets

outwash plains and valley trains

glacial melt water, choked with sediment, flows onto a flat surface, drops its load, builds a broad ramp like surface, and created braided systems; outwash plains are associated with ice sheets and valley trains are associated with mountain valleys

ice-contact deposits

meltwater flows over, within, and at the base of motionless ice deposits, stratified drifts that remain once the ice melts away

a kame

a steep-sided mound of sand and gravel deposited by a melting ice sheet.

an esker

a narrow, sinuous ridge

proglacial lakes

created when ice sheets and alpine glaciers can act as dams

pluvial lakes

the growth of ice sheets can cause the temperatures and evaporation to decrease in semiarid regions; form when precipitation occurs

plate tectonics

continents shift and move through geological time; continents were arranged differently in the past and changes occur in oceanic circulation

Milankovitch hypothesis

shape (eccentricity) of earth's orbit varies, angle of earth's axis (obliquity) changes, earth's axis wobbles (precession); changes in climate over the past several hundred thousand years are closely associated with variation in the geometry of earth's orbit

dry climate

one in which yearly precipitation is not as great as the potential for evaporation; dry regions cover 30% of earth;s land surface

mountain barriers

as air rises over a mountain, clouds form releasing precipitation on the windward side of the mountain

rainshadow

forms when air flowing over the leeward side of the mountain is dry

mechanical weathering

more prominent than in humid regions

chemical weathering

can occur over long spans of time; produces clay, thin soils, and oxidation of iron-rich sediments

ephemeral streams

only carry water in response to specific periods of rainfall

arid regions

typically have interior drainage because the intermittent streams do not flow to the ocean; erosion occurs without reference to the ocean

alluvial fan

a fan-shaped sediment deposit; coarse material deposited first

bajada

forms from the coalescing of multiple fans

playa lake

the dry, flat lake bed left after the water evaporates

bed load

carried by wind close to the surface; consists mostly of sand grains