Water exists everywhere on Earth, and covers 70% of its surface. 97% of this water is found in the oceans.

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1 10.1 Distribution of Water Water exists everywhere on Earth, and covers 70% of its surface. 97% of this water is found in the oceans. w Another 2% is ice and snow, leaving only 1% as fresh water found in the ground, rivers, lakes and streams. w Finding fresh water to drink is a challenge in many places, as most fresh water is under the ground. See page 362

2 The Water Cycle Earth is the only planet with water in all 3 states Water is continually cycling through the water cycle Solid Liquid = Melting Liquid Gas = Evaporation Gas Liquid = Condensation Liquid Solid = Solidify/Freeze Solid Gas = Sublimation Gas Solid = Deposition Heat energy from the Sun causes these changes to drive the water cycle. See page 364

3 The Water Cycle (continued) The water cycle occurs everywhere, not just oceans w Water evaporates when it is warmed, and then condenses in the atmosphere as clouds when it cools and falls as precipitation. The water then runs-off back to storage basins, or soaks into the ground. w A hydrologist is a scientist who studies water systems w An oceanographer studies oceans specifically See pages

4 10.2 How Ocean Water Differs from Fresh Water Ocean water s salinity = 200X greater than fresh water w Average salinity of oceans is 35 parts per thousand w Oceans at equator (evaporation) and poles (ice) have the highest salinity (removing water increases salinity) w Ocean locations near rivers have low salinity, due to addition of fresh water See page from the World Ocean Atlas 2001

5 Composition of Salt Water Salt water is composed of minerals dissolved during run-offs occurring over millions of years w Volcanic eruptions also release minerals from inside Earth w Sodium ions (Na + ) and chloride ions (Cl - ) are most common solids in ocean water w Na + ions and Cl - ions > 75% of all solids in ocean water w Mixed and joined in the ocean, NaCl is chemical name for salt See page 370

6 Density of Salt Water Density of ocean water (kg / m 3 ) = Mass (kg) Volume (m 3 ) w Density = how tightly packed the molecules are in an object w The density of salt water is near 1027 kg/m 3, whereas the density of fresh water is 1000 kg/m 3 w Less dense always floats on more dense Eg. warm air rises above cool air, and oil floats on water We float better in salt water than fresh water Salt water has slightly different properties than fresh water w Salt water freezes at 1.9 ºC rather than 0 0 C See page 371

7 10.3 Sources of Fresh Water Precipitation becomes run-off as gravity pulls water down into the groundwater, a lake or an ocean basin. Run-off increases if: w precipitation falls on rock, as soils allow water to soak in w heavy rainfall saturates the ground so water can t soak in w long periods of rainfall saturate the ground so water can t soak in w water can flow quickly down a steep slope, not having time to soak in w there is no vegetation, as plants help to absorb water and hold soil with their root systems w there is human development and no soils Human development often alters run-off See page

8 Drainage Basins Drainage basins are large areas where surface water all moves towards one main river w Run-off flows into streams and smaller rivers, which are tributaries of large rivers, forming a branching system w Large rivers are separated by very high ground called divides The Rocky Mountains form the Continental Divide, which divides BC and Alberta See page 379

9 Ground Water Ground water is water that soaks into the ground w Rock/ground with good porosity allows more water to enter w More pores (spaces in the rock/soil), the better the porosity w Permeability is a measure of how easily water can move through material w An aquifer is a layer of porous rock that allows ground water to flow, almost like a river below the surface. Humans get fresh water from w Reservoirs, natural or man-made w Wells, drilled into aquifers down to the water table, which is the top level of the zone of saturation. w The water table is very deep in deserts, but near the surface in swamps w The water table rises during wet seasons See page 380

10 Glaciers Almost 66% of all fresh water on Earth is in glaciers w Glaciers form from layers of snow falling over many years w Glaciers melt slowly under their own weight, and slowly flow downhill w Glaciers cover about 10% of the Earth s surface w Alpine glaciers (aka valley) found in mountains w Continental glaciers (aka ice sheets) cover huge areas of land. Eg. Greenland and Antarctia w Glaciers flow until they reach an ocean, where crevasses open and icebergs fall off reach an area where warm temps allow as much melting as re-freezing, or recede if they melt faster than they can freeze Take the Section 10.3 Quiz See page 381