(c) McGraw Hill Ryerson 2007 10.1 Distribution of Water Water exists everywhere on Earth, and covers...

(c) McGraw Hill Ryerson 2007

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. Another 2% is ice and snow, leaving only 1% as fresh water

found in the ground, rivers, lakes and streams.

Finding fresh water to drink is a challenge in many places, as most fresh water is under the ground.

See page 362


The Water Cycle

• Earth is the only planet with water in all 3 states• Water is continually cycling through the water cycle

• Heat energy from the Sun causes these changes to drive the water cycle.

See page 364

Solid Liquid = MeltingLiquid Gas = EvaporationGas Liquid = Condensation

Liquid Solid = Solidify/FreezeSolid Gas = SublimationGas Solid = Deposition


The Water Cycle (continued)

• The water cycle occurs everywhere, not just oceans 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.

A hydrologist is a scientist who studies water systems An oceanographer studies oceans specifically See pages 404 - 405

Take the Section 10.1 Quiz


10.2 How Ocean Water Differsfrom Fresh Water

• Ocean water’s salinity = 200X greater than fresh water Average salinity of oceans is 35 parts per thousand Oceans at equator (evaporation) and poles (ice) have the

highest salinity (removing water increases salinity) Ocean locations near rivers have low salinity, due to

addition of fresh water

See page 368 - 370

from the World Ocean Atlas 2001


Composition of Salt Water

• Salt water is composed of minerals dissolved during run-offs occurring over millions of years Volcanic eruptions also release minerals from inside Earth Sodium ions (Na+) and

chloride ions (Cl-) are most common solids in ocean water

Na+ ions and Cl- ions > 75% ofall solids in ocean water

Mixed and joined in the ocean, NaCl is chemical name for salt

See page 370


Density of Salt Water

•

Density = how tightly packed the molecules are in an object

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 Salt water freezes at –1.9 ºC

See page 371

Density of ocean water (kg /m3) =

Mass (kg)Volume (m3)



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: precipitation falls on rock, as soils allow water to soak in heavy rainfall saturates the ground so water can’t soak in long periods of rainfall saturate the ground so

water can’t soak in water can flow quickly down a steep slope, not

having time to soak in there is no vegetation, as plants help to absorb

water and hold soil with their root systems there is human development and no soils

• Human development often alters run-off See page 376 - 377


Drainage Basins

• Drainage basins are large areas where surface water all moves towards one main river Run-off flows into streams and

smaller rivers, which are tributaries of large rivers, forming a branching system

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


Ground Water

• Ground water is water that soaks into the ground Rock/ground with good porosity allows more water to enter More pores (spaces in the rock/soil), the better the porosity 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 Reservoirs, natural or man-made Wells, drilled into aquifers down

to the water table, which is the

top level of the zone of saturation. The water table is very deep in

deserts, but near the surface in swamps The water table rises during wet seasons See page 380


Glaciers

• Almost 66% of all fresh water on Earth is in glaciers Glaciers form from layers of snow falling over many years Glaciers melt slowly under their own weight, and slowly flow

downhill Glaciers cover about 10% of the Earth’s surface Alpine glaciers (aka valley) found in mountains Continental glaciers (aka ice sheets) cover huge areas of land.

Eg. Greenland and Antarctia 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 See page 381



10.4 Water’s Effect on ShapingEarth’s Surface

• Water is always moving due to the water cycle Quick changes can happen due to floods, storms or tsunamis Slower changes occur due to glaciers, run-off and rivers

• Water helps in weathering, erosion and deposition Weathering is the breaking down of rock into smaller pieces

Physical weathering (aka mechanical) - rocks broken down by force, but still remain as the same kind of rocks

Chemical weathering - rocks broken down by chemicals into different types of matter

Erosion is the movement of pieces of broken rock to another location

Deposition is the dropping, and building up, of pieces of rock (eg. river deltas) See page 386 - 388


Weathering by Water and Ice

• Physical weathering Occurs most quickly where the climate includes high levels of

precipitation and large temperature changes (between night and day, and also from season to season)

Ice wedging (aka frost wedging) weathers rocks due to the expansion of water as it freezes

• Chemical weathering Occurs most quickly where climate is warm, there is high levels

of rainfall and pollution Water + oxygen = much chemical weathering, including rusting

aka oxidation Plants also aid in chemical weathering

Lichens, decomposing plants See page 389


Weathering by Water and Ice (continued)

• Chemical weathering also occurs underground Water + carbon dioxide = carbonic acid, which dissolves

rock Groundwater becomes acidic, and reacts with calcium

carbonate in some rocks to dissolve the rocks Limestone has high levels of carbonate

Over time, large spaces are created underground Sinkholes, caves and karst are

formed this way

See page 390

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


Erosion by Water and Ice

• Erosion by water Moving water breaks down rock into sediment

Sediment can be eroded far away and deposited V-shaped valleys are carved by flowing water

Rapids create more weathering as water moves faster Ocean waves continually erode shoreline Gravity can cause landslides and avalanches

• Erosion by ice Glaciers once covered all of BC (2 km deep, 10 000 years ago)

leave striations (scratch marks) on rocks form U-shaped valleys can move large rocks long distances

See pages 392 - 393


Glacial Effects

See page 394

Arête Cirque Fiord (or fjord)

Hanging Valley

Horn

Narrow ridge (high ground) between two

cirques

Bowl-shaped valley at the

head of a glacier

A narrow inlet of ocean between

steep cliffs carved by glaciers

U-shaped valley cut off by a

bigger valley created by a larger glacier

Pyramid-shaped peak located

between threecirques

Images from http://pubs.usgs.gov/of/2004/1216/a/a.html


Deposition by Water and Ice

See page 395


• After erosion, sediments are eventually deposited A delta forms where a river empties into a calm basin Glaciers deposit many different forms of sediment

Erratic Esker Moraine Outwash

Large boulder deposited on the

ground by a glacier

Winding ridge of material deposited

by a stream running under a glacier

Ridge of rocky material deposited

by a glacier, are found at the sides

and farthest advance of a glacier.

Material deposited by water from

melting glaciers

Images from http://pubs.usgs.gov/of/2004/1216/a/a.html

(c) McGraw Hill Ryerson 2007 10.1 Distribution of Water Water exists everywhere on Earth, and covers...

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