Earth and Space Science Ms. Pollock Spring 2008

Fresh Water on the Earth’s Surface  Water one of most abundant substances on 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 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 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 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 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 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  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 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 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 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