Marshak, 16

Most groundwater is clever and pure enough to drink straight out of the ground. why?

-Rocks and sediment serve as natural filters capable of removing suspended solids-these solids get trapped in tiny pores or stick to the surfaces of clay flakes

Where the drips hit the floor, the resulting precipitate builds an upward-pointing cone called a ___

-stalagmite -which rises from the ground

Calculating groundwater flow rate are more complicated:

Darcy's Law is used to calculate this rate at a given location

Geyser:

an episodic fountain of hot, steamy water

Permeability:

the ease of flow

how does a hydraulic head flow?

-As a rule, groundwater flows from regions where it has higher hydraulic head to regions where it has lower hydraulic head -This implies: groundwater flows from locations where the water table is higher to locations where the table is lower

What happens to groundwater over time in the saturated zone?

-But in the saturated zone-the region below the water table-water flow tends to be more complex, for water moves in response to variations in pressure. -Pressure can cause groundwater to flow sideways or even upward (ex: stepping on a water filled balloon or watching a fountain shoot water up)

what happens during a geyser?

-Groundwater sinks and fills these fractures and absorbs heat from the rock. Because the boiling point of water-the temp at which it vaporizes-increases with growing pressure, hot groundwater at depth can remain in liquid form even if its temperature has become greater than the boiling point of water at earth's surface. -When the "superheated" groundwater begins to rise through a conduit toward the surface, the pressure in the groundwater decreases until eventually some of the water boils and transforms into steam -The pressure generated by the expansion of this team drives water upward in the fracture so that it spills out of the conduit at the ground surface. -When this spill happens, the pressure deeper in the conduit exerted by the weight of overlying water suddenly decreases. -This sudden drop in pressure causes the superheated water at depth to "flash" into steam instantly, and this steam quickly rises, ejecting all the water and steam above it from the conduit in a geyser eruption.

what is the unsaturated zone?

-Nearer the ground surface, this water only partially fills pores, so air remains in some of the open space.

The permeability of a material depends on several factors:

-Number of available conduits -Size of the conduits -Straightness of the conduits

The case of an unconfined aquifer: This location in groundwater is where the water table over a broad area is horizontal How is stress influenced?

-Pressure in groundwater at a specific point underground is caused only by the weight of the overlying water from that point up to the water table-the weight of overlying rock does not contribute to the pressure exeterneed on groundwater because the contact points between mineral grains bear the rocks weight. -In this ex above, pressure acting on water at a specific depth below the water table is the same everywhere

How to get water from an ordinary well?

-Pull the water up in a bucket or pump the water out. -As long as the rate at which groundwater fills the well exceeds the rate at which water is removed, the level of the water table near the well remains about the same. However, if people pump water out of the well too fast, then the water table sinks down around the well, known as drawdown, so that the water table becomes a downward-poriting, cone-shaped surface called a cone of depression.

The groundwater reservoir consists of the open spaces within sediment or rock underground. How does water get into this reservoir?

-Some get buried with sediment grains during deposition and get trapped when the rock lithifies. -Some bubbles out of magma that has intruded the crust. -But most water precipitates from the sky, as rain or snow, and falls on the land.

What happened in Florida with a sinkhole?

-The bedrock beneath the town consists of limestone. Groundwater, the liquid water that resides within sediment or rock under the surface of the wreath, had gradually dissolved the limestone over time, carving caverns (open rooms) underground. -The cavern collapsed. Soil and rock from up above sank into the opening, and a circular depression called a sinkhole developed. Everything dropped into the sinkhole.

How does the hydraulic head change with location underground?

-The results indicate that groundwater flows along concave-up curving path. -The curved paths eventually take groundwater form regions where the water table is high (under a hill) to regions where the water table is low (below a valley), but because of flow-path shape, some groundwater first descends along the first part of its path and then flows back along thee final part of its path

The best way to avoid groundwater contamination, or groundwater pollution, is to prevent waste products from entering groundwater in the first place

-They should be sealed in containers and located above impermeable bedrock so that they are isolated from aquifers. The storage area should be lined with plastic or clay as not only acts as an aquitard but also can bond contaminants -Spills? Chemicals may be absorbed by clay, oxygen in water may oxidize them, and bacteria in the water may metabolize them, turning them into a harmless substance -They can also use bioremediation-a technique that involves injecting oxygen and nutrients into a contaminated aquifer to foster growth of bacteria that can break down molecules of contaminants

what are examples of : the water tables shape mimicks in a subdued way, the shape of the overlying land surface?

-This means that the water table is higher beneath hills than beneath valleys -But the relief of the water table, meaning thee vertical distance between the higher and lowest elevations, tends to be less than that of the overlying land, so the water table tends to be smoother than the ground surface

how is some water drawn up from the water table? what is this layer known as?

-Typically, surface tension, the electrostatic attraction of water molecules to each other and to minerals surfaces, causes some water to seep up from the water table (aka water rises in a straw). -This water fills pores in a thin layer, known as the capillary fringe, just above the water table

Distinctive features form in geothermal regions as a result of the eruption of hot water:

-Where hot water rises into soils rich in volcanic ash and clay, a viscous slurry forms and fills goopy mud pots -Bubbles of steam rising through the mud cause it to splatter about -Where geothermal waters spill out of natural springs and then cool, dissolved minerals in the water precipitate, forming mounds or terraces of travertine and other chemical sedimentary rock

Kras have the following landforms:

-Where surface streams intersect cracks (joint) or holes that link to caverns or passageways below, the water cascades downward into the subsurface and vanishes. -These are disappearing streams. They may flow through passageways underground and later emerge from a cave entrance downstream -Where the ground collapses into an underground cavern below, a sinkhole develops -As most of the cavern network collapses, formed walls between caverns are steep-sided ridges, and remnants of cavern roofs can stand as natural bridges

Springs can occur:

-Where the ground surface intersects the water table; such springs may add water to lakes or streams -Where flowing groundwater reaches a steep, impermeable barrier, and pressure pushes the groundwater up to the earth's surface along the barrier -Where a perched water table intersects the surface of a hill -Where a network of interconnected fractures in intersects the water table and provides a conduit for groundwater to reach the ground surface -Where downward-percolating water runs into an aquitard and migrates along the top surface of the aquitard to a hillslope -Where the ground surface intersects a natural fracture (joint) that taps a confined aquifer in which the pressure is sufficient to drive the water to thee surface; such occurrence are artesian springs

When the water table drops below the level of a chamber, the chamber becomes

-an open space filled with air

Cave:

-any underground open space, most or all of which does not receive any direct sunlight -A cave may grow due to the dissolution of rock or to the removal of rock by rockfalls or erosion -Many caves open up along a cliff face, whereas others lie completely underground

where do many large cavern networks develop?

-develop in limestone bedrock because limestone dissolves relatively easily in corrosive groundwater -The corrosive component in groundwater is dilute carbonic acid which forms when water absorbs carbon dioxide from materials, such as soil, that it has passed through as it percolates down. -When carbonic acid comes in contact with calcite, in limestone, it reacts to produce a solution containing dissolved HCO3 and Ca ions.

Darcy represented the velocity of flow by a quantity called the ____, which....

-discharge, -meaning the volume of water passing through an imaginary vertical plane perpendicular to the groundwater flow in a given time. It depends on: the hydraulic gradient, the area, and the hydraulic conductivity

Groundwater that has passed through limestone or dolostone contains what?

-dissolved calcium and magnesium ions. -Such water, known as hard water, can be a problem because carbonate minerals precipitate from it to form a scale that clogs pipes and soap won't develop a lather in hard water.

In places where downward-percolating groundwater continuing dissolved calcite emerges from the ceiling or walls of the cave, the surface of the cave changes. As the water emerges into the air, it evaporates slightly and releases some dissolved carbon dioxide. As a result, calcite precipitates out of the water, producing _____.

-dripstone -which can accumulate to form travertine and intricately shaped formations of speleothems

When groundwater fills the pore space underground, it holds grains apart, for water cannot be compressed. However, the extraction of water from a pore

-eliminates the support holding the grains apart, because the air that replaces the water is a gas, and gases can be compressed. -As a result, the grains pack more closely together. Such pore collapse decreases a rock's porosity and permeability.

Fresh groundwater lies in a layer above saline (salty) water. Along coasts, the saline water enters the aquifer from the adjacent ocean. Because freshwater is less dense than saline water, it ____ above the saline water.

-floats -If people pump water out of the well too quickly, the boundary between the two types of water rises. And if this boundary risers above the base of thee well, the well will yield useless saline water

Water becomes a more effective solvent when hot, so

-hot groundwater dissolves minerals from rock that it passes through. -Consequently, hot springs tend to emit mineralized water. -In nature, the mineral content and temperature of hot springs can incubate life, and as a result, natural pools of geothermal water may be brightly colored from thermophilic (heat loving) bacteria and archaea that thrive in hot water and eat the sulfur-containing minerals dissolved in groundwater

The cone of depression that develops around a well produces a

-local slope to the water table. -The resulting change in the hydraulic gradient may locally reverse the flow direction. -Such reversals can allow contamination seeping out of a septic tank to head toward the well

When groundwater is extracted at a rate faster than it can be resupplied, the water table gradually becomes _____ over a board region

-lower -As a result, existing wells, springs, and rivers dry up and to continue tapping into the water supply, so we have to dig progressively deeper -Without enough rain or snow in the recharge area, water didn't infiltrate the water table

Springs are:

-natural outlets from which groundwater flows or seeps onto the earth's surface -Springs are a source of freshwater for drinking or irrigation, without having to dig or drill -Some springs spill groundwater onto dry land; others bubbles though the bed of a stream or a lake.

But, soon the soda straw fills up and the water migrates down the margin of the cone to form a more massive, solid icicle-like cone called a

-stalactite -which grows downward from the ceiling

what is an ordinary well?

-the base of the well penetrates an aquifer below the water table -Water from the pore space in the aquifer seeps into the well and fills it to the level of the water table -note: drilling into an aquitard, or into any material that lies above the water table, will not supply water, and yield a dry well

what is a simple summary of how groundwater flows?

-the velocity of groundwater flow depends on the slope of the water table and on the permeability of the material through which the groundwater moves. -Groundwater flows faster through high-permeability materials than it does through low-permeability materials, and it flows faster in regions where the water table has a steep slope than it does in regions where the water table has a gentle slope. -Ex: groundwater flows relatively slowly through a low-permeability aquifer under the great plains but it flows relatively quickly through a high-permeability aquifer under a steep hillslope

area: (darcys law)

-this quantity represents the cross-sectional area of the imaginary plane through which the groundwater passes

primary porosity:

-this refers to the open space that remains in a sediment after deposition, or in a rock after its formation -this exists because grains don't fit together perfectly during deposition, because grains don't grow to fill all space during crystallization, or because open spaces do not completely fill with cement

what is the hydraulic gradient? (Darcys law)

-this represents the change in hydraulic head per unit of distance between two locations, as measured along the flow path. -Typically, the slow of thee water table is so small that the path length is almost the same as the horizontal distance between two points, so the hydraulic gradient roughly equals the slope of the water table

hydraulic conductivity: (darcys law):

-this represents the ease with which a fluid can flow through a material. -It depends primarily on the permeability of the material, but also on other factors such as the viscosity of the fluid

Permeability of a material refers to

-to the ease in which fluids can pass through a material. -For permeability to exist, passageways or conduits must link pores to each other -These conduits may be spaces between grains or they may be cracks

What are the two reasons why Groundwater moves much more slowly than surface water?

1) groundwater moves by percolating through a complex crooked network of tiny conduits, so it must travel a much greater distance than it would if it could follow a straight path. -2) friction between groundwater and conduit walls slows down the water flow

Although groundwater accounts for ______ of the liquid freshwater on the planet, accessible groundwater cannot always be replenished quickly

95%

when does a perched water table occur?

A perched water table occurs where a mound of groundwater becomes trapped above a localized aquitard that lies above the regional water table

Different earth materials have different porosities

A poorly cemented sandstone may have a porosity of up to 30% , whereas a granite generally has a porosity of less than 1%

what causes groundwater depletion?

By pumping water out of the ground at a faster rate than nature replaces it

Species living in caves have evolved some unusual characteristics.

Cave fish lose their pigment and in some cases their eyes.

what happens in life in caves?

Colonies of bacteria metabolize sulfur-containing minerals in this water produce thick mats of living ooze in the complete darkness of the cave. Long gobs of this bacteria slowly drip from the ceiling.

However, we can not drink water with dissolved chemicals. how is this proved in an example?

Groundwater that has been underground for a long period of time or has passed through salt-containing strata, may be too saline to be suitable for irrigation or for drinking.

what is saline intrusion?

If people pump water out of the well too quickly, the boundary between the two types of water rises. And if this boundary risers above the base of thee well, the well will yield useless saline water

The depth of the water table below ground surface varies with location

In temperature or tropical regions, where it rains frequently and water often seeps into the ground, the water table lies within a few meters of the earth's surface. Here, a channel or depression whose floor lies below the water table will fill with liquid water. As a result, the surface of a permanent stream, lake, or mash effectively defines the level of thee water table in temperate or tropical regions

What happens to groundwater over time in the unsaturated zone?

In the unsaturated zone-the region between the ground surface and the water table-water percolates straight down in response to the downward pull of gravity, like the water passing through a drip coffee maker

There are two basic kinds of porosity:

Primary and secondary

how do ordinary wells function during seasons?

Some ordinary wells only function during the rainy season, when the water table risers above the base of the well. During the dry seasons, the water table lies below the base of seasonal wells so the well becomes dry

what is one reason why hot springs exist?

They occur where groundwater, as it slows flows from recharge area to discharge area, follows a flow path that travels many kilometers down into the crust, where bedrock, naturally warm due to the geothermal gradient, heats the groundwater. The curving path of flow eventually carries the groundwater back up to the surface

what is a perched water table?

This is a mound of groundwater accumulates above such aquitard lense -it is a lens-shaped layers of impermeable rock (such as shale) may lie within a thick aquifer

what is a soda straw?

Where water drips from the ceiling of the cave, calcite initially preceptes around the outside of the drip, forming a delicate, hollow tube

What is a hot spring?

a conduit from which groundwater ranging in temperature from about 30 to 104 celsius flows

Because joints commonly occur in orthogonal systems, passages may form

a grid

An aquifer is:

a high porosity and high permeability rock. Some aquifers are unconfined, and some are confined

Also, arsenic, a highly toxic chemical that enters groundwater when

arsenic-breaking minerals dissolve in groundwater

Number of available conduits:

as the number of available conduits increases, permeability increases

How does infiltrating water moves downward from the earth's surface into the subsurface?

by percolating along cracks and conduits that connect pores.

the top part of the unsaturated zone usually consists of what?

consists of soil, so the water in this part can also be called soil moisture

Groundwater that has passed through iron-bearing rocks may contain

dissolved iron oxide that precipitates to form rust stains

Groundwater that occurs above hydrocarbon reserves may contain

dissolved methane, which also comes out of solution near the earth's surface, to form flammable bubbles

To measure the hydraulic head at a point in an aquifer, you:

drill a vertical hole down to the point and insert a pipe in the hope. The height above a reference elevation to which water rises higher in the pipe represents the hydrolytic heard: water rises higher in the pipe where the head is higher

what is thee second reason why hot springs evist?

hot springs develop in geothermal regions, places where igneous activity increases the geothermal gradient substantially, so that hot rock lies close to the ground surface.

The energy available to drive the flow of groundwater, at a given location, by the _____

hydraulic head

Water moves among many reservoirs during the

hydrologic cycle

what is a confined aquifer?

is isolated from the earth's surface by an aquitard, so water can't infiltrate directly

Secondary porosity:

it refers to new pore space produced in a rock subsequent to the rocks lithification. -Ex: secondary porosity can develop when a rock cracks and opposing walls of the cracks do not fit together perfectly or when fluids passing through a rock dissolve grains or cements, thereby producing open cavities.

why doees the elevation of the water table vary?

it varies because groundwater movies so slowly through rock and sediment that it cannot quickly assume a horizontal surface -So when rain falls on a hill and water infiltrates down to the water table, the water table rises a little -When it doesn't rain, the water table sinks a little, but this movement takes place so slowly that when rain falls again, the water table rises before it has had time to sink very far

Springs supply water to

lush vegetation that grows around a spring. Where a spring occurs in a desert, an oasis (an area where plants flourish in an otherwise bone-dry landscape-stands out as a patch of green against the desert)

where does a geyser occur?

overlies a network of irregular fractures in very hot rock; one of these fractures connects to the ground surface

what is an artesian well?

penetrates a confined aquifer in which water has enough pressure to rise on its own to a level above the top surface of the aquifer -If this level lies below the ground surface, the well is a non flowing artesian well -If the level above the ground surface, it is a flowing artesian well

Water flows easily through a ______ material, wheras it flows slowly or not at all though an _____ material

permeable / impermeable

how is porosity different than permeability?

porosity and permeability are not the same feature- a material whose pores are isolated from each other can have high porosity but low permeability

Passages in cave networks typically follow

pre-existing joints, which provide openings along which groundwater can flow faster

what is an unconfined aquifer?

reaches up to the earth's surface, so that water can infiltrate into it directly from the surface

Most groundwater resides in where?

relatively small open spaces between grains of sediment, between grains of seemingly solid rock, or within cracks of various sizes underground, in groundwater

kras:

rocky ground -is used to describe a region with abundant rock exposures

Aquifers:

sediments or rocks with high permeability and porosity

Aquitards:

sediments or rocks with lower permeability, regardless of porosity

An aquitard:

slows, or retards, the motion of groundwater

The water table specifies what?

the horizon that separates the unsaturated zone above from the saturated zone below.

Chambers develop where

the limestone dissolves more easily and where groundwater flow is fastest

Some groundwater contains dissolved hydrogen sulfide, a poisonous gas that forms due to

the metabolic process of certain underground bacteria. This corrosive gas comes out of solution when groundwater rises to the surface and the pressure in it decreases.

groundwater is...

the second-largest reservoir of freshwater on the planet, after glaciers of antarctica and greenland

what is porosity?

the total amount of open space within a material (This is a percentage) Ex: 20% porosity, 20% of the block consists of open space

what is the metamophor of the first level of crust?

the upper part of the crust is like a giant sponge that can soak up water that falls from the sky

In hilly regions, the water table is not a planar surface. Rather....

the water tables shape mimicks in a subdued way, the shape of the overlying land surface.

what are wells?

they are holes or pits that provide access to groundwater

what is the summary of darcys law?

this equation means that as the hydraulic gradient increases, discharge increases, and that as hydraulic conductivity increases, discharge increases. Put in simpler terms, the flow rate of groundwater increases as the permeability increases, and as the slope of the water table gets steeper

because of the density of saline water?

this groundwater tends to be deeper, so a boundary between fresh groundwater above and saline groundwater below may exist in the subsurface

what is a pore?

this is any open space within a volume of sediment or within a body of rock

what is infiltration?

this is when water sinks or percolates downward into the ground

Cavern:

this term is for caves formed mostly by dissolution or for particularly large caves -Commonly, a region may contain many interconnected caverns that together comprise a cavern network

If the process of dripstone formation continues long enough, stalagmites merge with overlying stalactites to produce

travertine columns

The shape of a cave network reflects

variations in permeability and in the composition of the rock from which the caves formed

Size of the conduits:

water can travel fastener through widener conduits than through narrower ones

Straightness of the conduits:

water can travel faster through straight conduits than through crooked ones

what is the saturated zone?

water completely fills, or saturates, pore space. -Strictly, groundwater is used only for subsurface water in the saturated zone

Ordinary wells and artesian wells are distinguished based on:

whether water in the well rises under its own pressure