Groundwater and Karst Topography Ch 92

7/29/2019 Groundwater and Karst Topography Ch 92

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Groundwater and Karst

TopographyChapter 9, Section 2


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The Hydrologic Cycle (WATER CYCLE)


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Evaporation

Condensation

Precipitation

Runoff


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Soil is made up of many small rock andmineral fragments.

Holes, cracks, and crevices exist in therock underlying the soil.

Water that soaks into the ground and

collects in these pores and empty spacesbecome part ofgroundwater.

Groundwater


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Water is recharged to the ground-water

system by percolation of water from

precipitation and then flows to the stream

through the ground-water system.


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14 % of all freshwater on Earth exists as

groundwater, 30 times more water than is

contained in all of Earths lakes and rivers.

Water that soaks into the ground becomes

a part of the groundwatersystem.


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A groundwatersystem is similar to a river

system.

Instead of having channels that connectdifferent parts of a drainage basin, the

groundwater system has connecting

pores.


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Soil and rock are permeable if the pore

spaces are connected and watercan pass

through them easily.

If a rock or sediment has few pore spaces,

or they are not well connected, then theflow of groundwater is blocked.

These materials are impermeable, which

means that watercannot pass through them.

Granite and clay are impermeable;

sandstone is permeable.


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Permeabi l i ty


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Groundwater keeps going deeper into the

Earths crust until it reaches a layer of

impermeable rock.

At this point, the water stops moving

down.

Water begins filling up the pores in the

rocks above. The layer ofpermeablerock that lets water move freely is an

aquifer.


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The zone of aeration is the first layer of

soil that is permeable. Water and air pass

through this layer easily.


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The area where all of the rocks are filled

with wateris called the zone ofsaturation.

The upper surface of this zone is called

the water table.


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GROUNDWATER FEATURES


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Groundwater Zones

Zone of

Saturation

Zone of

Aeration Precipitation

Body of water

Earths Surface Water Table


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Many people get their water from

groundwaterthrough wells that have been

drilled into the zone ofsaturation.

The supply of groundwater is limited.

During a drought the water table drops,which is why you should conserve water.


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People get the majority of their water from

wells. A good well extends deep into the

zone ofsaturation, where groundwaterflows into the well and a pump brings it to

the surface.

If too much water is pumped out, then

wells can go dry.

The land level can sink from the weightof the sediments above the now-empty

pore spaces.


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What does a normal household

well look like?

Water flows into a

well and then a pump

brings the water to

the surface. Wells can go dry if too

many are located in

one area, or if a

drought takes place.


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ARTESIAN WELL


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Water pumped from the ground-water system causes

the water table to lower and alters the direction of

ground-water movement. Some water that flowed to the

stream no longer does so and some water may bedrawn in from the stream into the ground-water system,

thereby reducing the amount of streamflow.


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CONES OF DEPRESSION


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Shallow wells go dry due to

excessive pumping


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In some places, the water table is so

close to Earths surface that water

flows out and forms a spring.

Springs are found on hillsides orother places where the watertable

meets a sloping surface.


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SPRING FORMATION


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HOT SPRINGS


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Hot Spring


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A geyseris a hot spring that erupts

periodically, shooting waterand steam into

the air.

Groundwater is heated to high

temperatures from magma under the

Earths surface. As the water heats, it

expands, forcing water out of the ground

along with steam, as the remaining

water boils.Old Faithful in Yellowstone National Park

is a famous geyser.


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GEYSERS: OLD FAITHFUL

http://www.yellowstone.net/russfinley/tour/video/oldfaith2.rm
http://www.yellowstone.net/russfinley/tour/video/oldfaith2.rmhttp://www.yellowstone.net/russfinley/tour/video/oldfaith2.rm


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Picture of a geyser in action!


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Geyser


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Groundwater mixes with carbon dioxide to

form carbonic acid.

Limestone is a rock that is easily dissolved

by carbonic acid.

As the acidic groundwater moves through

pores in limestone, the rock dissolves,

enlarging cracks until an underground

opening called a cave is formed.


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Groundwater not only dissolves limestoneto make caves, but it also can makedeposits on the insides of caves.

Water dripping from the cave wallscontains calcium ions dissolved from the

limestone. If the waterevaporates whilehanging from the ceiling, the calciumcarbonate is left behind and builds up to

form a stalactite.

Where water drops fall to the floor, astalagmite forms.


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Cave

Development


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CAVE ENTRANCE


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Disappearing Stream


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Disappearing Stream

NATURAL CHIMNEYS


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NATURAL CHIMNEYS

NATURAL BRIDGE


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NATURAL BRIDGE


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If underground rock is dissolved near the

surface a sinkhole may form.

A sinkhole is a depression on the surface

of the ground that forms when the roof of

a cave collapses, or when rock near thesurface dissolves.

These are common in areas that have lotsoflimestone and enough rain water to

keep the groundwater system supplied

with water.

Sinkhole


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Sinkhole

SINKHOLE


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SINKHOLE


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Karst topography is common in the

Valley and Ridge Province of Virginia,

where limestone is abundant.

KARST TOPOGRAPHY FEATURES


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KARST TOPOGRAPHY FEATURES


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H I t G d t


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Human Impact on Groundwater

Groundwater accounts for 20% of all waterused in the U.S.

Unwise use of this valuable resource can

damage or deplete groundwater reservoirs

Some of the problems related to groundwater

use include:

overpumping-lowering the water table

subsidence

contamination


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Pollutants


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Pollutants

Contaminants introduced at the land surface may

infiltrate to the water table and flow towards a point

of discharge, either the well or the stream.

A SOURCE OF GROUNDWATER


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A SOURCE OF GROUNDWATER

CONTAMINATION: SEPTIC TANKS

Contamination results in a decline


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Contamination results in a decline

in water quality.


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ANOTHER SOURCE OF POLLUTION:


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STORAGE TANKS

YET ANOTHER SOURCE OF POLLUTION:


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LANDFILLS

Groundwater Moves Usually


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Groundwater Moves Usually

Slowly


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Groundwater and Karst Topography Ch 92

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