Download Unit 4 – Water Systems on Earth Chapter 10 – The water cycle plays

Unit 4 – Water Systems on Earth
Chapter 10 – The water cycle plays a vital role on Earth.
10.1 Distribution of Water
-water exists everywhere on Earth, covers 70% of its surface
-97% of this water is found in oceans
-another 2% is ice/snow, leaving only 1% as fresh water found in the
ground, rivers, lakes, streams
-finding freshwater to drink = challenge in many places, as most is
underground
*The Water Cycle*
-Earth is only planet with all three states/phases
-solid (in form of ice, snow, glaciers)
-liquid (in form of oceans, lakes streams)
-gas (in form of water vapour in atmosphere)
-water cycle: the continual movement of water between oceans, land,
atmosphere
☇occurs everywhere
☇water evaporates when warmed
☇condenses in the atmosphere as clouds
☇when cools, falls as precipitation
☇then runs off back to storage basins, or soaks into ground
*solid  liquid = melting
*liquid  gas = evaporation
*gas  liquid = condensation
*liquid  solid = solidification
*solid  gas = sublimation
*gas  solid = deposition
-heat energy from Sun causes these changes to drive cycle
-hydrologist: a scientist who studies Earth’s water systems and helps find
solutions to problems related to water quality and quantity
-oceanographer: a scientist who studies oceans specifically
1
10.2 How Ocean Water Differs from Fresh Water
-salinity: the amount of salt dissolved in water
-ocean water’s salinity = 200x greater than fresh water
-average salinity of ocean is 35 parts per thousand (35‰)
-oceans at equator (evaporation) and poles (ice) have highest salinity
-equator – high rates of evaporation; when water in ocean transforms
into vapour in air, leaves salt behind
-poles – when water freezes and changes into ice, leaves salt behind
☇removing water increases salinity
-oceans near rivers have low salinity, due to addition of fresh water
*Composition of Salt Water*
-salt water is composed of minerals dissolved during run-offs occurring over
millions of years
☇run off: water that is not absorbed immediately by Earth’s surface but
flows downhill over the land and buildings and into water bodies and sewers
-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 add up to more than 85% of all the dissolved
solids in the ocean
-mixed and joined in the ocean, NaCl = sodium chloride (salt)
*Density of Salt Water*
-density of ocean water (kg/m3) = mass (kg)/volume (m3)
-density: how tightly packed the molecules are in an object
-less dense always floats on more dense; ex: warm air rises above cool
-we float better in salt water than fresh water
-ocean water-density=1027 kg/m3; fresh water-density=1000 kg/m3
*Freezing Point of Salt Water*
-salt water has slightly different properties than fresh water
-fresh water freezes: 0°C; salt water freezes: approx. -1.9°C
-freezing point of salt is lower than freezing point of water –
thus, salt in water lowers the freezing point of solution
2
10.3 Sources of Fresh Water
-precipitation becomes run off as gravity pulls water down into groundwater,
a lake or an ocean basin
-gravity: the attractive force between objects; the force that causes
objects to be pulled toward the centre of Earth
*Factors Affecting Run-off*
-run off increases if:
-precipitation falls on rock, as soils allow water to soak in
the nature of the ground material
-heavy rainfall saturates the ground so water can’t soak in
the amount of rain
-long periods of rainfall saturate the ground so water can’t soak in
the length of time it rains
-water can flow quickly down a steep slope, not having time to soak in
the slope of the land
-there is no vegetation, as plants help to absorb water and hold soil with
their root systems
the amount of vegetation
-there is human development and no soils
the amount of development in the area
-human development often alters run-off
*Drainage Basins*
-drainage basin: the area of land on which precipitation falls and drains into
a common river; also called a watershed – similar to sink
-run-off flows into streams and other 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
*Ground Water*
-ground water: water that soaks into the ground
-rock/ground with good porosity allows more water to enter
-more pores (spaces in rock/soil), the better the porosity
-aquifer: layer of porous rock that allows ground water to flow, almost
like a river below the surface
-humans get fresh water from:
-reservoirs: large natural or artificial lakes or holding ponds used to
collect and store water for human use
3
-wells, drilled into aquifers down to the water table, which is the top
level of the zone of saturation
-water table: in the ground, the level beneath which porous
rocks are filled with water
-very deep in deserts, but near the surface in swamps
-rise during wet seasons
*Glaciers*
-almost 66% of all fresh water on Earth is in glaciers
-glaciers form from layers of snow falling over many years
-melt slowly under own weight, and slowly flow downhill
-covers about 10% of the Earth’s surface
-Alpine glaciers (aka valley) found in mountains
-Continental glaciers (aka ice sheets) cover huge areas of land; ex: Greenland
-glaciers flow until they:
-reach an ocean, where crevasses open and icebergs fall of
-crevasse: deep crack that forms in a glacier
-iceberg: large chunk of ice that breaks off a glacier into ocean
-reach an area where warm temps allow as much melting as re-freezing,
or recede if they melt faster than they can freeze
10.4 Water’s Effect on Shaping Earth’s Surface
-snow has helped shape the rock surface of BC
-large sheets of moving ice can tear, scrape, and carry solid rock
-water in its liquid and gas form is also constantly changing the landscape
around you
-these changes can happen quickly, or over thousands/millions of years
*Weathering, Erosion, and Deposition*
-weathering: the process of breaking down rock into smaller fragments
-physical weathering: rocks are broken down by physical means
-rocks being scratched to bits by harder rocks
-chemical weathering: a chemical reaction causes rocks to break down
-an upright gravestone gradually wearing away
-biological weathering: caused by plants or animals
-tree root breaking through rock
-after rock becomes weakened and broken down, it can be carried away in
the process of erosion
-erosion: the transport of sediments from one place to another by
agents such as water, glaciers, gravity, and wind
4
-deposition: process in which eroded sediments and other material are
dropped and left by water/ice, creating built-up landforms such as deltas,
eskers
-sediments deposited in layers may eventually turn into solid
sedimentary rock
*Weathering by Water and Ice*
-physical weathering is greatest in climates with a lot of moisture in the air,
or rain and snow, and where there are large temperature differences
between winter/summer
-water in the cracks/pores freezes and expands, breaking the rock
into pieces; called ice/frost wedging
-chemical weathering is greatest in climates with high temperatures, a lot of
rain, and high levels of pollution
-water and oxygen can trigger chemical reactions that decompose
minerals and rock
-plants die and decompose, releasing chemicals that break down rocks
-when rainwater mixes with carbon dioxide, the water droplets
become acidic
☇when this water reaches ground, the acid dissolves carbonate rock
-when ground water with carbonic calcium carbonate in their
composition (‘carbonate rocks’), the result is like what happens when
vinegar and baking soda mix – but without fizzing
- gaps in the rock can create underground caves, sinkholes, karst
-sinkhole: large circular depression in the ground caused by collapse of
an underground cave
-karst: an area with many sinkholes
5
*Erosion by Water and Ice*
-two main transporters, or agents, of erosion are moving water and glaciers;
they work closely with gravity
-moving water can physically break down rock material into sediment
-sediment is transported and deposited in large amounts elsewhere
-rivers in mountainous or steep regions have high energy and carve
deep valleys that look like letter V in cross section
-rapids, where the water moves very quickly over exposed pieces of
rock, can form in a steep and rocky river channel
-ocean waves are also a powerful forces, eroding coastlines
-landslides (a sudden, rapid movement of rock material down the slope of a
hill/mountain) occur when rain soaks the slopes of steep hills and mountains
-an avalanche is a landslide of ice and snow
-glaciers have shaped much of our province’s landscapes
-moving water and glaciers deposit the materials they pick up
-as ice sheets are pulled slowly downhill by gravity, the scrape and carve the
land they are passing over
-striations: scratch marks cut into rock by glaciers slowly moving over
-other features created by glaciers:
☇arête: narrow ridge (high ground) between two cirques
☇cirque: bowl-shaped valley at the head of a glacier
☇fiord: a narrow inlet of ocean between steep cliffs carved by glaciers
☇hanging valley: U-shaped valley cut off by a bigger valley created by a
larger glacier
☇horn: pyramid-shaped peak located between three cirques
*Deposition by Water and Ice*
-delta: an area of built-up sediment deposited by a river where the river
empties into a n ocean or lake
-when fast-moving river water enters a body of water, it slows down
and begins to drop the sediments’ it has carried downstream
-pattern created by deposited sediments is usually triangular
-glaciers deposits rock material when they melt
-some notable glacier-deposited features:
☇erratic: large boulder deposited on the ground by a glacier
☇esker: winding ridge of material deposited by stream running under glacier
☇moraine: ridge of rocky material deposited by glacier; can be found at
sides and farthest advance of a glacier
☇outwash: material deposited by water from melting glaciers
6
Chapter 11 – Oceans control the water cycle.
11.1 Ocean Basins
-surface of ocean floor is as varied as the land
-five major oceans, from largest to smallest: Pacific, Atlantic, India,
Southern, Arctic
-low points in ocean = basins
-oceans are vital to life, as they control temperature, create weather
patterns, and provide water for water cycles
*The Origin of Ocean Water*
-oceans have filled over hundreds of millions of years
-scientists believe that oceans are more than 3 billion years old
-water may have originally been released from volcanic eruptions, or arrived
on Earth via icy comets
-water trapped inside volcanic materials released into atmosphere,
water vapour; like steam escaping from kettle
-water vapour cooled/condensed, fell to Earth’s surface -precipitation
-gravity cause water to flow downhill, so vast amounts of water that
fell began collecting in lowest parts of Earth’s surface – ocean basins
*Features of the Ocean Floor*
-although the word ‘basin’ sounds flat, many features found on land, mountain
ranges, valleys, flat plains, canyons, and volcanoes also exist on ocean floor
-ocean basin: deep, wide depressions in Earth’s surface that contain oceans
-continental margins: the part of continents that lies under ocean and
includes the continental shelf, the continental slope, and the continental rise
☇Ocean Basins
-largest changes to ocean basin occur through movement of tectonic plates,
although there is also erosion via storms, earthquakes, icebergs
-greatest influence in shaping ocean floor is result of tectonic processes
-tectonic processes: the movements of Earth’s tectonic plates
(crust/upper mantle broken into large rock slabs) as the float over
Earth’s molten layer
-magma heats up from heat energy in Earth’s core; molten rock rises;
this pressure forces two places apart
-two types of tectonic plates: oceanic/continental; oceanic denser
-mid-ocean ridge
7
Ocean Basins
• The largest changes to the ocean basin occur through
the movement of tectonic plates, although there is also
erosion via storms, earthquakes and icebergs.
• Mid-ocean ridges occur where new rock is forced up,
and ocean floor spreads outward.
 The Mid-Atlantic Ridge is the largest example on Earth
 The Juan de Fuca plate lies
200 km off Vancouver Island
• A trench forms when
the dense oceanic plates
run into, and slide under,
the continental plates.
See pages 406 - 407
(c) McGraw Hill Ryerson 2007
8