Groundwater and Karst Topography

Groundwater and Karst Groundwater and Karst TopographyTopography

Chapter 9, Section 2Chapter 9, Section 2

The Hydrologic Cycle (WATER CYCLE)The Hydrologic Cycle (WATER CYCLE)

Evaporation

Condensation

Precipitation

Runoff

Soil is made up of many small rock and Soil is made up of many small rock and mineralmineral fragments. fragments.

Holes, Holes, crackscracks,, and crevices exist in the and crevices exist in the rock underlying the soil.rock underlying the soil.

Water that soaks into the ground and Water that soaks into the ground and collects in these pores and empty collects in these pores and empty spacesspaces become part of become part of groundwater.groundwater.

Groundwater

Water is recharged to the ground-water Water is recharged to the ground-water system by percolation of water from system by percolation of water from precipitation and then flows to the stream precipitation and then flows to the stream through the ground-water system. through the ground-water system.

14 %14 % of all freshwater on Earth exists as of all freshwater on Earth exists as groundwater, groundwater, 30 30 times more water than is times more water than is contained in all of Earth’s lakes and rivers.contained in all of Earth’s lakes and rivers.

Water that soaks into the ground becomes Water that soaks into the ground becomes a part of the a part of the groundwatergroundwater system. system.

A groundwater A groundwater systemsystem is similar to a is similar to a river river system.system.

Instead of having Instead of having channelschannels that connect that connect different parts of a drainage different parts of a drainage basinbasin, the , the groundwater system has connecting groundwater system has connecting porespores..

Soil and rock are Soil and rock are permeablepermeable if the pore if the pore spaces are spaces are connectedconnected and and waterwater can pass can pass through them easily.through them easily.

If a rock or sediment has few pore spaces, If a rock or sediment has few pore spaces, or they are not well connected, then the or they are not well connected, then the flow of groundwater is flow of groundwater is blockedblocked.. These materials are These materials are impermeableimpermeable, which , which

means that means that waterwater cannot pass through them. cannot pass through them.

Granite and clay are Granite and clay are impermeableimpermeable; ; sandstone is sandstone is permeablepermeable..

PermeabilityPermeability

Groundwater keeps going deeper into the Groundwater keeps going deeper into the Earth’s Earth’s crustcrust until it reaches a layer of until it reaches a layer of impermeableimpermeable rock. rock.

At this point, the water stops moving At this point, the water stops moving downdown..

Water begins filling up the pores in the Water begins filling up the pores in the rocksrocks above. The layer of above. The layer of permeablepermeable rock that lets water move freely is an rock that lets water move freely is an aquiferaquifer..

The The zone of aerationzone of aeration is the first layer of is the first layer of soil that is permeable. Water and air pass soil that is permeable. Water and air pass through this layer easily.through this layer easily.

The area where all of the rocks are filled The area where all of the rocks are filled with with waterwater is called the is called the zonezone of of saturationsaturation..

The upper surface of this zone is called The upper surface of this zone is called the the water tablewater table..

GROUNDWATER FEATURESGROUNDWATER FEATURES

Groundwater ZonesGroundwater Zones

Zone of Zone of SaturationSaturation

Zone of Zone of AerationAeration

PrecipitationPrecipitation Body of waterBody of water Earth’s SurfaceEarth’s Surface Water TableWater Table

Many people get their water from Many people get their water from groundwatergroundwater through wells that have been through wells that have been drilled into the zone of drilled into the zone of saturation.saturation.

The supply of groundwater is The supply of groundwater is limitedlimited. . During a During a droughtdrought the water table drops, the water table drops, which is why you should conserve water.which is why you should conserve water.

People get the majority of their water from People get the majority of their water from wellswells. A good well extends deep into the . A good well extends deep into the zone of zone of saturationsaturation, where groundwater , where groundwater flows into the well and a flows into the well and a pumppump brings it to brings it to the surface.the surface.

If too much water is pumped out, then If too much water is pumped out, then wells can go wells can go drydry..

The land level can The land level can sinksink from the weight from the weight of the of the sedimentssediments above the now-empty above the now-empty pore spaces.pore spaces.

What does a normal household well What does a normal household well look like?look like?

Water flows into a Water flows into a well and then a pump well and then a pump brings the water to brings the water to the surface.the surface.

Wells can go dry if too Wells can go dry if too many are located in many are located in one area, or if a one area, or if a drought takes place.drought takes place.

ARTESIAN WELLARTESIAN WELL

Water pumped from the ground-water system causes Water pumped from the ground-water system causes the water table to lower and alters the direction of the water table to lower and alters the direction of ground-water movement. Some water that flowed to the ground-water movement. Some water that flowed to the stream no longer does so and some water may be stream no longer does so and some water may be drawn in from the stream into the ground-water system, drawn in from the stream into the ground-water system, thereby reducing the amount of streamflow. thereby reducing the amount of streamflow.

CONES OF DEPRESSIONCONES OF DEPRESSION

Shallow wells go dry due to Shallow wells go dry due to excessive pumpingexcessive pumping

In some places, the water table is so In some places, the water table is so close to Earth’s surface that water close to Earth’s surface that water flows out and forms a flows out and forms a springspring..

Springs are found on Springs are found on hillsideshillsides or or other places where the water other places where the water tabletable meets a sloping surface.meets a sloping surface.

SPRING FORMATIONSPRING FORMATION

HOT SPRINGSHOT SPRINGS

Hot SpringHot Spring

A A geysergeyser is a hot spring that erupts is a hot spring that erupts periodically, shooting periodically, shooting waterwater and and steamsteam into into the air.the air. Groundwater is heated to high Groundwater is heated to high

temperatures from temperatures from magmamagma under the under the Earth’s surface. As the water heats, it Earth’s surface. As the water heats, it expandsexpands, forcing water out of the ground , forcing water out of the ground along with along with steamsteam, as the remaining , as the remaining water boils.water boils.

Old Old FaithfulFaithful in Yellowstone National Park in Yellowstone National Park is a famous geyser. is a famous geyser.

GEYSERS: OLD FAITHFULGEYSERS: OLD FAITHFUL

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

Picture of a geyser in action!Picture of a geyser in action!

GeyserGeyser

Groundwater mixes with carbon Groundwater mixes with carbon dioxidedioxide to to form carbonic form carbonic acidacid..

LimestoneLimestone is a rock that is easily dissolved is a rock that is easily dissolved by carbonic acid.by carbonic acid.

As the acidic groundwater moves through As the acidic groundwater moves through pores in limestone, the rock pores in limestone, the rock dissolvesdissolves, , enlarging cracks until an underground enlarging cracks until an underground opening called a opening called a cavecave is formed. is formed.

Groundwater not only dissolves limestone Groundwater not only dissolves limestone to make to make cavescaves, but it also can make , but it also can make depositsdeposits on the insides of caves. on the insides of caves.

Water dripping from the cave walls Water dripping from the cave walls contains contains calciumcalcium ions dissolved from the ions dissolved from the limestone. If the water limestone. If the water evaporatesevaporates while while hanging from the ceiling, the calcium hanging from the ceiling, the calcium carbonatecarbonate is left behind and builds up to is left behind and builds up to form a form a stalactitestalactite..

Where water drops fall to the floor, a Where water drops fall to the floor, a stalagmitestalagmite forms. forms.

Cave Cave DevelopmentDevelopment

CAVE ENTRANCECAVE ENTRANCE

Disappearing StreamDisappearing Stream

NATURAL CHIMNEYSNATURAL CHIMNEYS

NATURAL BRIDGENATURAL BRIDGE

If underground If underground rockrock is dissolved near the is dissolved near the surface a surface a sinkholesinkhole may form. may form.

A sinkhole is a A sinkhole is a depressiondepression on the surface on the surface of the ground that forms when the roof of of the ground that forms when the roof of a a cave cave collapses, or when rock near the collapses, or when rock near the surface surface dissolvesdissolves..

These are common in areas that have lots These are common in areas that have lots of of limestonelimestone and enough rain water to and enough rain water to keep the groundwater system supplied keep the groundwater system supplied with with waterwater..

SinkholeSinkhole

SINKHOLESINKHOLE

KarstKarst topography is common in the topography is common in the Valley and Ridge Province of Virginia, Valley and Ridge Province of Virginia, where limestone is abundant. where limestone is abundant.

KARST TOPOGRAPHY FEATURESKARST TOPOGRAPHY FEATURES

Human Impact on GroundwaterHuman Impact on Groundwater

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

Unwise use of this valuable resource can Unwise use of this valuable resource can damage or deplete groundwater reservoirsdamage or deplete groundwater reservoirs

Some of the problems related to groundwater Some of the problems related to groundwater use include:use include:

overpumpingoverpumping-lowering the water table-lowering the water table subsidencesubsidence contaminationcontamination

PollutantsPollutants

Contaminants introduced at the land surface may Contaminants introduced at the land surface may infiltrate to the water table and flow towards a point infiltrate to the water table and flow towards a point of discharge, either the well or the stream.of discharge, either the well or the stream.

A SOURCE OF GROUNDWATER A SOURCE OF GROUNDWATER CONTAMINATION: CONTAMINATION: SEPTIC TANKSSEPTIC TANKS

Contamination results in a decline Contamination results in a decline in water quality.in water quality.

ANOTHER SOURCE OF POLLUTION: ANOTHER SOURCE OF POLLUTION: STORAGE TANKSSTORAGE TANKS

YET ANOTHER SOURCE OF POLLUTION: YET ANOTHER SOURCE OF POLLUTION: LANDFILLSLANDFILLS

Groundwater Moves – Usually Groundwater Moves – Usually SlowlySlowly