Transcript Water - Images

Earth and Space Science
Ms. Pollock
Spring 2008
WATER
Fresh Water on the Earth’s
Surface
 Water one of most abundant substances on
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Earth
Oceans on 70% of Earth’s surface
97% of Earth’s water in oceans
Salty, so cannot be used by most organisms
Fresh water 3% of Earth’s water
Most fresh water locked in icecaps and
glaciers
15% of Earth’s freshwater available for use
The Water Cycle
 Prevents Earth from running out of water
 Water moving or standing
 Moving – rivers, streams, springs
 Standing – ponds, lakes, swampy wetlands
 Water cycle – continuous movement of water
from oceans and freshwater sources to air
and land, and then back to oceans
 Also called hydrologic cycle
Steps of the Water Cycle
 Evaporation
 Sun heats water on Earth’s surface to vapor
 Water rises and is carried by wind over lands and
oceans
 Condensation
 Air containing water vapor cooled
 Droplets formed
 Heavy droplets form clouds
 Precipitation
 Droplets in clouds too numerous and heavy
 Fall to Earth as rain, snow, sleet, or hail
Groundwater
 Water that remains in the ground after
evaporation
 Eventually flows underground to oceans
 Reenters water cycle from oceans
Frozen Water
 Glacier – large mass of moving ice and snow
 Formed from new snow piled on top of old
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snow – pressure creates ice
Formed in cold areas – high in mountains,
near North and South poles
Snow never completely melted
Thick, heavy layers formed; begins to move
2% of Earth’s available fresh water
Valley Glaciers
 Long, narrow glaciers that move downhill
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between mountains
Follow channels formed by past running
water
Bend and twist to fit shape of landforms
Ice stays together but cracks on surface
(crevasses)
Picks up rocks, carries them in the ice; cuts
into landforms
Valley Glaciers
 Found in Alaska, Washington, New
Hampshire mountains
 Some water melted as glacier moves –
meltwater
 Meltwater nearly pure
 Freshwater source for some cities
 Used for hydroelectric power
Continental Glaciers
 Polar regions
 Thick sheets of snow and ice; also called polar
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ice sheets
Millions of square kilometers of surface
Several thousand meters thick
Greenland 80% covered
Antarctica 90% covered
Icebergs
 Formed as large chunks of ice break off
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continental glaciers at edge of sea
Can be as large as Rhode Island
Mainly from Greenland and Antarctica
Major hazard to ships; constant patrols
Hopes to one day be able to transport to
areas in need of fresh water
Running Water
 Rivers and streams necessary for irrigation,
power generation, drinking, transportation,
fishing, boating, swimming
 Formed by surface runoff
 Affected by type and condition of soil,
number of plants, seasons
 Watershed – land area in which surface runoff
drains into river or system of rivers and
streams
Running Water
 Watersheds small or large; determine fresh
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water that flows into oceans
Amount of water in river an speed of water
important to usefulness of river
Fast-moving rivers lots of water, but also soil,
pebbles, and other sediments; cloudy
appearance
Slow-moving rivers clearer, better sources of
fresh water
Pollution transferred down to oceans
Standing Water
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Ponds or lakes, depending on size
Continually receive runoff from land; slow to dry up
Low areas in watershed
Lakes – deep depressions in Earth’s crust filled with
fresh water
 Sometimes natural obstruction of river or stream
 Most frequent in high areas, once covered by glaciers
 Ponds – shallow depressions in Earth’s crust filled
with fresh water
 Sunlight able to penetrate to bottom
 More plant growth than lakes
Standing Water
 Reservoirs – artificial lake formed by
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damming a river or stream in a low-lying area
Near cities and towns
Control water flow during periods of heavy
rain and runoff
Drinking water source
Irrigation water
Hydroelectric power
Fresh Water Beneath Earth’s
Surface
 There is more fresh water below the surface
of the land than in all of the lakes and
reservoirs on the Earth’s surface.
 Rain, snow, sleet or hail that has soaked into
the ground
Groundwater
 Continuous supply of fresh water for many
areas
 Precipitation filtered down through pores in
rocks and soil
 Permeable – material through which water
can move quickly
 Sand, gravel
 Impermeable – material through which water
cannot move quickly
 clay
Underground Zones
 Water eventually exposed to layer of rock
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that is impermeable
Zone of saturation – underground region in
which all pores filled with water
Area above zone of saturation where ground
not as wet; pores filled mostly with air
Zone of aeration – drier region in which pores
are filled mostly with air
Water table – boundary between zone of
saturation and zone of aeration
Underground Zones
 Water table easy to find at seashore
 Never deep at large body of water
 Near hills or mountains probably deep in
ground
 Water table also affected by climate and dry
droughts
Aquifers
 Layers of sandstone, gravel, sand, or cracked
limestone; water moves sideways through
 May be between layers of impermeable rock
 Well dug or drilled into aquifer; groundwater
moves into well hole and forms pool
 May or may not require pumping
 Artesian well – well from which water flows on its
own without pumping
Groundwater Formations
 Caverns (caves) formed
 Limestone – water moves down through soil,
combines with carbon dioxide to form weak
acid that dissolves limestone, water enters
cracks in limestone that widen to produce
caves
 Sometimes large underground caverns with
many passageways
 Stalactites and stalagmites formed from
dissolved substances in groundwater
Water as a Solvent
 Most common substance on Earth
 Solid, liquid, or gas
 Continuous cycle, changing forms as it goes
 Water molecule smallest particle that has all
properties of water.
 Two hydrogens and one oxygen
 Slight negative charge on oxygen, slight
positive charge on hydrogen (polarity)
Water as a Solvent
 Polarity makes water a solvent.
 Can dissolve many compounds
 Solutions formed
 Compounds seemingly disappear
 Opposite “poles” attracting different atoms
 Soft drinks
 Medicines
 Fluoride
 Liquid fertilizers
Hardness of Water
 Water taste, odor, and appearance different
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from place to place
Dependent on amount and type of material
dissolved
Drinking water either from ground or surface
source
May be “hard” or “soft”
Depends on types of rocks and soils
contacted
Hardness of Water
 Hard water – contains large amounts of
dissolved minerals, especially calcium and
magnesium
 Soap does not lather easily.
 Build-up of minerals in plumbing
 Soft water – does not contain minerals
calcium and magnesium
 Some water naturally softened by rocks and
minerals as passed through
Quality of Water
 Necessary for all life on Earth, so needs to be of
good quality
 Many sources becoming polluted
 Natural filters soil and sand, but many filter
sources polluted by careless dumping
 Limits amount of wildlife that can live in water
and potable drinking water
 Destroys recreational areas
 Phosphates and nitrates
 Federal laws, treatment plants