NOTES: Water on Earth: Water Resources and Distribution
Surface Water
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Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean;
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.007 % of total water, yet it is used more to supply drinking water and to irrigate crops
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Surface water is naturally replenished by precipitation and naturally lost through discharge to evaporation and
sub-surface seepage into the ground.
Groundwater
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Water found under the earth’s surface,
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water underlies the Earth's surface almost everywhere, beneath hills, mountains, plains, and deserts.
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2nd largest storehouse of freshwater, 30.1%
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Groundwater may occur close to the land surface, as in a marsh, or it may lie many hundreds of feet below the
surface, as in some arid areas of the West.
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Water at very shallow depths might be just a few hours old;
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At moderate depth, it may be 100 years old;
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and at great depth or after having flowed long distances from places of entry, water may be several
thousands of years old.
Purple area - ground is saturated below the water table
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The saturated zone below the water table has water that fills the tiny spaces (pores) between rock
particles and the cracks (fractures) of the rocks.
Pink area – The ground above the water table may be wet to a certain degree, but it does not stay saturated.
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The dirt and rock in this unsaturated zone contain air and some water and support the vegetation on the
Earth.
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Groundwater is an important part of the water cycle.
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It’s the part of precipitation that seeps down through the soil until it reaches rock material that is
saturated with water.
Groundwater slowly moves underground generally at a downward angle (because of gravity), a process called
percolation
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may eventually seep into streams, lakes, and oceans.
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Some layers have rocks that are more porous than others, and here water moves more freely (in a horizontal
manner) through the earth
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Water in the ground is stored in the spaces between rock particles
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No, there are no underground rivers or lakes.
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Gravity doesn't pull water all the way to the center of the Earth.
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Deep in the bedrock there are rock layers made of dense material, such as granite, or material that
water has a hard time penetrating, such as clay.
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These layers may be underneath the porous rock layers and, thus, act as a confining layer to stop the
vertical (downward) movement of water.
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Since it is more difficult for the water to go any deeper, it tends to pool in the porous layers and flow in
a more horizontal direction across the aquifer toward an exposed surface-water body, like a river.
NOTES: Water on Earth: Water Resources and Distribution
Aquifer
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The saturated zone beneath the water table is called an aquifer
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Aquifers are huge storehouses of freshwater.
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Water from precipitation continually seeps into the ground to recharge the aquifers, while at the same time
water from underground aquifers continually recharges rivers through seepage.
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Water movement in aquifers is highly dependent of the permeability of the aquifer material.
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Permeable material contains interconnected cracks or spaces that are both numerous enough and large
enough to allow water to move freely.
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Blue area -ground below the water table is saturated with water.
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The "unsaturated zone" above the water table (the greenish area) still contains water (after all, plants' roots live
in this area), but it is not totally saturated with water.
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You can see this in the two drawings at the bottom of the diagram, which show a close-up of how water is
stored in between underground rock particles.
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Water movement in aquifers is highly dependent of the pearmeablility of the aquifer material.
•
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Permeable material contains interconnected cracks or spaces that are both numerous enough and large
enough to allow water to move freely.
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In some permeable materials groundwater may move several metres in a day; in other places, it moves
only a few centimetres in a century.
Groundwater moves very slowly through relatively impermeable materials such as clay and shale.
Wetland
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There are places that are covered with water sometimes, while other times they dry out.
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They provide a home, or habitat, for many different plants, birds, and animals, including endangered species.
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Many fish start their lives in wetlands, where they are protected from danger.
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Wetlands help to store floodwater before it runs off and causes damage.
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One other important job of wetlands is protecting land and communities by blocking the force of wind and
waves from storms coming in from the ocean.
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The amount of water found in wetlands depends on the season and on how much rain and snow falls over time.
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Sometimes wetlands are freshwater, sometimes they are saltwater.
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Soil and plants in wetlands also trap tiny particles, like sediment, as they clean up water headed for the ocean
NOTES: Water on Earth: Water Resources and Distribution
Oceans
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The ocean is the largest storehouse of water
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about 97 percent of all water is in the oceans
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Much more water is "in storage“ in the oceans for long periods of time than is actually moving through the
water cycle
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Water is saline if it has a concentration of more than 1,000 ppm of dissolved salts; ocean water contains about
35,000 ppm of salt.
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Ocean Movement :
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Of course the oceans are always in movement.
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The moon influences daily tides
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Winds create waves
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Currents and "rivers" in the oceans that move massive amounts of water around the world.
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These movements have a great deal of influence on the water cycle and climate.
Lakes
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A lake is where surface-water runoff (and maybe some ground-water seepage) have accumulated in a low spot,
relative to the surrounding countryside.
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It's not that the water that forms lakes get trapped, but that the water entering a lake comes in faster
than it can escape, either via outflow in a river, seepage into the ground, or by evaporation
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The Earth has a tremendous variety of freshwater lakes, from fishing ponds to Lake Superior (the world's
largest), to many reservoirs.
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Most lakes contain fresh water, but some, especially those where water cannot escape via a river, can be salty
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Most lakes support a lot of aquatic life,
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In fact, some lakes, such as the Great Salt Lake, are saltier than the oceans.
but the Dead Sea isn't called "Dead" for nothing -- it is too salty for aquatic life!
Lakes formed by the erosive force of ancient glaciers
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such as the Great Lakes, can be thousands of feet deep
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Some very large lakes may be only a few dozen feet deep -- Lake Pontchartrain in Louisiana has a
maximum depth of only about 15 feet.
Some of the salty lakes were formed in ancient times when they were connected to seas and when rainfall may
have been heavier.
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These lakes have been shrinking since the last ice age.
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The ancient Lake Bonneville in the United States was once as big as Lake Michigan, and the Great Salt
Lake was once about 14 times as large as it is now.
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Lakes are highly value/d for their recreational, aesthetic and scenic qualities, and the water they contain is one
of the most treasured of our natural resources.
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Lakes constitute important habitats and food resources for a diverse array of fish, aquatic life, and wildlife, but
lake ecosystems are fragile.
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Lake ecosystems can undergo rapid environmental changes, often leading to significant declines in their
aesthetic, recreational, and aquatic ecosystem functions.
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Exposed to external effects from the atmosphere, their watersheds, and ground water, lakes are subject to
change through time.
NOTES: Water on Earth: Water Resources and Distribution
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Human activities can further accelerate the rates of change. If the causes of the changes are known,
however, human intervention (lake-management practices) sometimes can control, or even reverse,
detrimental changes.
Reservoir
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Is the same thing as a lake in many peoples' minds. But, in fact, a reservoir is a manmade lake
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Created when a dam is built on a river.
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River water backs up behind the dam creating a reservoir.
River vs. Stream vs. Creek
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Rivers? Streams? Creeks? They are all names for water flowing on the Earth's surface.
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As far as the Water Science site is concerned, they are pretty much interchangeable.
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creeks as the smallest of the three, with streams being in the middle, and rivers being the largest.
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Rivers have been used for thousands of years to turn wheels to operate machinery for things such as millwork,
metalwork, and grinding agricultural items
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Over time, moving water can wear down rocks and dig deep into the ground. That's called erosion.
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Rivers may move fast enough to carry pieces of soil, called sediment, along with large rocks.
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Even slow rivers can erode rocks and carry sand, soil, and even pollution.
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Most of the water you see flowing in rivers comes from precipitation runoff from the land surface alongside the
river.
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A river is nothing more than surface water finding its way over land from a higher altitude to a lower altitude, all
due to gravity.
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When rain falls on the land, it either seeps into the ground or becomes runoff, which flows downhill into
rivers and lakes, on its journey towards the seas.
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Flowing water finds its way downhill initially as small creeks.
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As small creeks flow downhill they merge to form larger streams and rivers.
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Rivers eventually end up flowing into the oceans.
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If water flows to a place that is surrounded by higher land on all sides, a lake will form. If people have built a
dam to hinder a river's flow, the lake that forms is a reservoir.
Estuary
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Wherever fresh water from rivers mixes with salt water from oceans, that is called an estuary.
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Estuaries provide a habitat for sea life, birds, and animals.
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In the water of an estuary, you find fish and other creatures that spend part of their lives in the ocean and part
of their lives in rivers.
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Estuaries are often popular fishing areas.
Watershed
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A watershed is the area of land where all of the water that falls in it and drains off of it goes into the same place.
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Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers
that drain into Chesapeake Bay, where it enters the Atlantic Ocean.
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Watershed
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A watershed is an area of land that drains all the streams and rainfall to a common outlet such as the outflow of
a reservoir, mouth of a bay, or any point along a stream channel.
NOTES: Water on Earth: Water Resources and Distribution
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The word watershed is sometimes used interchangeably with drainage basin or catchment.
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Ridges and hills that separate two watersheds are called the drainage divide.
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The watershed consists of surface water--lakes, streams, reservoirs, and wetlands--and all the underlying ground
water.
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Larger watersheds contain many smaller watersheds.
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It all depends on the outflow point; all of the land that drains water to the outflow point is the watershed for
that outflow location.
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Watersheds are important because the streamflow and the water quality of a river are affected by things,
human-induced or not, happening in the land area "above" the river-outflow point
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Factors that Affect Watershed Water Flow:
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Precipitation: The greatest factor controlling streamflow, by far, is the amount of precipitiation that falls in the watershed as rain or
snow. However, not all precipitation that falls in a watershed flows out, and a stream will often continue to flow where there is no direct
runoff from recent precipitation.
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Infiltration: When rain falls on dry ground, some of the water soaks in, or infiltrates the soil. Some water that infiltrates will remain in the
shallow soil layer, where it will gradually move downhill, through the soil, and eventually enters the stream by seepage into the stream
bank. Some of the water may infiltrate much deeper, recharging ground-water aquifers. Water may travel long distances or remain in
storage for long periods before returning to the surface. The amount of water that will soak in over time depends on several
characteristics of the watershed:
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Soil characteristics: In Georgia, clayey and rockey soils of the northern areas absorb less water at a slower rate than sandy soils,
such as in Georgia's Coastal Plain. Soils absorbing less water results in more runoff overland into streams.
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Soil saturation: Like a wet sponge, soil already saturated from previous rainfall can't absorb much more ... thus more rainfall
will become surface runoff.
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Land cover: Some land covers have a great impact on infiltration and rainfall runoff. Impervious surfaces, such as parking lots,
roads, and developments, act as a "fast lane" for rainfall - right into storm drains that drain directly into streams. Flooding
becomes more prevalent as the area of impervious surfaces increase.
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Slope of the land: Water falling on steeply-sloped land runs off more quickly than water falling on flat land.
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Evaporation: Water from rainfall returns to the atmosphere largely through evaporation. The amount of evaporation depends on
temperature, solar radiation, wind, atmospheric pressure, and other factors.
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Transpiration: The root systems of plants absorb water from the surrounding soil in various amounts. Most of this water moves through
the plant and escapes into the atmosphere through the leaves. Transpiration is controlled by the same factors as evaporation, and by the
characteristics and density of the vegetation. Vegetation slows runoff and allows water to seep into the ground.
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Storage: Reservoirs store water and increase the amount of water that evaporates and infiltrates. The storage and release of water in
reservoirs can have a significant effect on the streamflow patterns of the river below the dam.
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Water use by people: Uses of a stream might range from a few homeowners and businesses pumping small amounts of water to irrigate
their lawns to large amounts of water withdrawals for irrigation, industries, mining, and to supply populations with drinking water.
Erosion
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Erosion is the process by which material is removed from a region of the Earth surface.
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It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material
under the force of gravity
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It can occur by weathering and transport of solids (sediment, soil, rock and other particles) in the natural
environment, and leads to the deposition of these materials elsewhere.
Sedimentation/turbidity Increases in accumulation and/or resuspension of sediments can be a detriment to
water quality and habitat for many aquatic species.
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Such events usually are caused by heavy rains that produce erosion and intense runoff, carrying heavy
sediment loads into lakes.
The soil type affects the potential for runoff and erosion.
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The physical characteristics of the substrate determine the extent, nature, and quality of ground-water
inflows and outflows.
NOTES: Water on Earth: Water Resources and Distribution
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These are primary factors affecting the lake’s chemistry, because of transfers between water and
sediments, and input of sediment, minerals, and nutrients from the watershed by runoff water flowing
into the lake.
Glacier
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Glaciers store about 69% of the world's freshwater
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During the last ice age (when glaciers covered more land area than today) the sea level was about 400 feet
lower than it is today.
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if all land ice melted the seas would rise about 70 meters (about 230 feet).
At that time, glaciers covered almost one-third of the land.
Almost 10 percent of the world's land mass is currently covered with glaciers,
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mostly in places like Greenland and Antarctica.
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Glaciers are important features in the hydrologic cycle and affect the volume, variability, and water quality of
runoff in areas where they occur
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In a way, glaciers are just frozen rivers of ice flowing downhill.
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Glaciers begin life as snowflakes.
•
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When the snowfall in an area far exceeds the melting that occurs during summer, glaciers start to form.
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The weight of the accumulated snow compresses the fallen snow into ice.
These "rivers" of ice are tremendously heavy, and if they are on land that has a downhill slope the whole ice
patch starts to slowly grind its way downhill.
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You can imagine how a billion-ton ice cube can rearrange the landscape as it slowly grinds its way
overland.
These glaciers can vary greatly in size, from a football-field sized patch to a river a hundred miles (161
kilometers) long.
Clouds: Water Storage in the Atmosphere
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Although the atmosphere may not be a great storehouse of water, it is the superhighway used to move water
around the globe.
•
Evaporation and transpiration change liquid water into vapor, which ascends into the atmosphere due to rising
air currents.
•
Cooler temperatures aloft allow the vapor to condense into clouds and strong winds move the clouds around
the world until the water falls as precipitation to replenish the earthbound parts of the water cycle.
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Water is in the air on cloudless days, too
About 90 percent of water in the atmosphere is produced by evaporation from water bodies, while the other 10
percent comes from transpiration from plants.