BC Science 8

Chapter 10 - The Water Cycle plays a vital role on Earth

10.1 Distribution of Water

. 70% of the Earth’s surface is covered in water.

. 97% of all that water is found in oceans

. 3% of the Earth’s water is fresh water

. 2% of fresh water is frozen in large areas of ice (Greenland, Antarctica)

Eric Hamber Secondary 1 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre The Water Cycle

. The Water Cycle is the process by which water on Earth changes from state to state.

. The 3 states are:

1. solid…. ice, snow and glaciers 2. liquid... oceans, lakes, and streams 3. gas…... water vapour in the atmosphere

. In the water cycle, there is no beginning or end.

. The water cycle happens because heat energy is constantly being added or taken away from water in its various states, causing all of these processes to occur.

1. Heat from the sun is what drives the water cycle.

2. As ocean water is heated by the Sun, the surface water molecules evaporate.

3. This water vapour rises into the atmosphere and is moved around the globe by winds.

4. When the air is cooled, condensation begins to occur and water droplets form.

5. When enough of these small droplets come together, clouds are created.

6. Clouds may release their load of water as rain, snow, or another form of precipitation; some falling back to the ocean and some onto the land.

7. Much of the water that reaches land gradually flows into streams and rivers, eventually returning to the ocean where the process begins again.

Eric Hamber Secondary 2 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre How Does Water Change State?

Water, like other types of matter, can change state when it is heated or cooled.

. Evaporation is a change of state from a liquid to a gas. (ex. Steam from a hot kettle)

. Condensation is a change of state from a gas to a liquid (ex. Water droplets that form on a window if you let a kettle boil too long)

. Melting is a change of state from a solid to a liquid. (ex. An ice cube melting)

. Solidification is a change of state from a liquid to a solid. (ex. Cooling water to its freezing point - 0º C turns it too ice)

Eric Hamber Secondary 3 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Sublimation is a change of state from a solid directly to a gas. (ex. Preservation of food by freeze-drying involves sublimation of water from food in a frozen state under vacuum)

. Deposition is a change of state from a gas directly to a solid. (ex. Frost forming on windows on very cold days)

. A hydrologist is a person who studies Earth’s water systems and helps find solutions to problems of water quality and quantity.

. Oceanographers are people who study ocean systems specifically.

Eric Hamber Secondary 4 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre 10.2 How Ocean Water Differs from Fresh Water

. Salinity is the amount of salt dissolved in water.

. Ocean water is more than 200x saltier than fresh water.

. Salinity in sea water is higher closer to the equator because of high rates of evaporation. When ocean water transforms into vapour in the air, it leaves the salt behind.

. Salinity in sea water is also higher near the North and South Poles, because when water freezes and changes into ice, it also leaves salt behind.

. Salinity is usually lower near continents than in the middle part of the ocean, because the fresh water from the rivers empties into the ocean and dilutes the salt water.

Composition of Salt Water

. Salt comes from the water that has been running off the land for millions of year.

. Most of the rainfall seeps into the ground and then into streams and rivers, picking up salt and other substances, where it then travels to the ocean.

. Volcanoes contribute dissolved solids by releasing large amounts of sulfur, fluorine, chlorine, and hydrogen into ocean water. Eruptions on land spew similar materials into the atmosphere where they then fall into the ocean or Earth’s surface.

Eric Hamber Secondary 5 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Sodium ions (Na+) and Chloride ions (Cl-) add up to more than 85% of all the dissolved solids in the ocean.

. Na and Cl form a compound called (NaCl), the chemical name for salt.

. In the ocean, these dissolved solids get mixed together by the constant motion of the water.

Eric Hamber Secondary 6 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre Density of Salt Water

. Density is a measure of the mass of an object of a given volume. (how tightly packed together that material is in the object)

. Density is measured in kilograms per cubic metre (kg/m3)

. Ocean water is denser than fresh water because of the amount of salt in it.

. Ocean water has a density of 1027 kg/m3 and fresh water has a density of 1000 kg/m3

. Ocean water has a lower freezing point than fresh water; this means that ocean water freezes at a lower temperature than fresh water does.

. Ocean water’s freezing point is approximately -1.90C; and fresh water’s freezing point is 00C

10.3 Sources of Fresh Water

. Only about 1% of all of Earth’s fresh water supply is easily accessible.

. Most of the fresh water is trapped in ice, in Greenland and Antarctica, and not available for human use.

. Available fresh water is found wherever water falling as rain and snow runs off the land and is collected in lakes, rivers, streams, and underground.

. Run-off is the water that is not absorbed immediately by Earth’s surface but flows downhill over the land and buildings and into water bodies and sewers

. Run-off is essential for filling the lakes, streams, and rivers that in turn help to keep the oceans filling with water.

Eric Hamber Secondary 7 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . The amount of run-off is affected by :

1. The nature of the ground material (covered in rock; results in an increase of run-off. Mostly soil; results in a decrease of run-off due to the ground’s ability to absorb water better)

2. The amount of rain (heavy rain; ground becomes saturated so there is an increase in run-off)

3. The length of time it rains (rain for long periods of time; an increase in run-off)

4. The slope of the land (very steep; the faster the water flows downhill the water cannot be easily absorbed by the ground resulting in an increase in run-off)

5. The amount of vegetation (grass, trees, and shrubs absorb water, so areas with little vegetation will have a greater amount of run-off)

6. The amount of development in the area (where there is a lot of pavement or concrete on the ground, water is usually channeled into storm sewers resulting in an increase in run- off)

. Gravity is the force that pulls everything toward the centre of Earth. Rain hitting pavement or hard rock will flow along the ground until it hits a low point on the surface or finds its way into a stream.

Eric Hamber Secondary 8 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Drainage Basin is the area of land on which precipitation falls and works its way into a common river. (also known as a watershed)

. A divide is an area of very high ground that usually separates one drainage basin from another. (ex. The Rocky Mountains form the Continental Divide)

Eric Hamber Secondary 9 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Ground Water is the water that makes its way into the spaces or pores of rock.

. Ground water flows from areas of higher elevation to lower elevations.

. A layer of rock that is porous and allows water to flow through it is called an aquifer.

. A reservoir is a large human-made or natural lake that stores water until it is needed.

. In rural areas, wells may be drilled or dug into the ground to a depth where water can be found; this depth is called the water table. (ex. the water table in a desert is much deeper than the water table in a forest beside a lake)

. The water table lies at the zone of saturation.

. Glaciers are large blocks or sheets of ice that slowly flow downhill.

Eric Hamber Secondary 10 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Almost 2/3 of the world’s fresh water is trapped in glaciers.

. There are 2 types of glaciers: Alpine glaciers (form in mountains) and Continental glaciers (arctic, Antarctic and Greenland)

. Glaciers affect the water cycle by holding water as ice. Less water evaporates from glaciers than from liquid bodies of water.

. A glacier will continue to slide down a slope:

a) If the glacier reaches an ocean, the ice will slowly spill over the edge of the land mass toward the water where deep crevasses (cracks) form along the front of the glacier. Icebergs (large chunks of ice) break off and crash into the ocean.

b) If the glacier reaches an elevation where the temperature is warm enough to make the glacier melt faster than the gravity can keep it creeping along, it will stop moving.

c) If temperatures increase, the glacier may even recede (melt back up the slope)….ALL glaciers in BC and around the world are receding

10.4 Water’s Effect on Shaping Earth’s Surface

. Water has the ability to reshape Earth’s surface, wearing away mountains, carving deep canyons, and creating huge underground caves.

. Weathering and Erosion are the 2 main processes by which water breaks down Earth’s landscapes.

. Deposition is the process by which water builds up features on the landscape.

Eric Hamber Secondary 11 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . Weathering causes changes that break down rock into smaller fragments. (is a slower process than erosion…can take thousands of years)

. 2 types of weathering: physical weathering and chemical weathering.

. Physical weathering: the changes are called physical weathering if the rock that breaks down stays the same type of rock. (rocks are being scratched and broken by harder rocks)

. Chemical weathering: the changes are called chemical weathering if the rock that breaks down becomes a different substance. (a chemical reaction causes rocks to break down; the minerals in the rocks change their composition and the rock becomes weaker)

. Biological Weathering: If physical or chemical weathering has been caused by a plant or animal, the process is referred to as biological weathering.

. Erosion moves large and small rock pieces from one place to another and can occur quickly.(water, glaciers, gravity, and wind are the main transporters of erosion)

. Deposition drops or leaves rock pieces that have been carried by water from one place to another, therefore building up the landscape. Deposition is responsible for building features such as sand dunes and deltas.

Weathering by Water and Ice Eric Hamber Secondary 12 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . 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 summer and winter or between daytime and nighttime.

. Water collects in the cracks and pores of rocks, and when it freezes it expands, breaking the rock into pieces. (ice or frost wedging)

. Chemical Weathering is greatest in climates with high temperatures, a lot of slightly acidic rainfall, and high levels of pollution (acid rain) in the air. Water and oxygen in the atmosphere can trigger chemical reactions that decompose the minerals making up rock. When it reaches the ground, the acidic rainwater dissolves some substances from rock on Earth’s surface. Acidic rain water dissolves rock that has calcium carbonate in it, and over time large gaps form large hollows in the rock (underground caves) or above ground (sinkholes)

. A karst is an area of land that has a lot of sinkholes.

Eric Hamber Secondary 13 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre Erosion by Water and Ice

Moving Water, Glaciers and Gravity are 3 main transporters of erosion.

Moving Water

. Moving Water breaks down rock material into tiny pieces (sediment)

. Sediment can be transported thousands of kilometers and dropped into large amounts elsewhere.

. Water that forces itself into cracks in rocks can weather the rock into pieces and carry them downstream.

. Rivers in mountainous or steep regions carve deep valleys, and where a river channel is very rocky and steep, rapids can form. (water moves rapidly over exposed pieces of rock, and erodes the landscape quickly)

. Ocean waves pound against the land, causing rocky coastlines to erode.

Glaciers Eric Hamber Secondary 14 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . As glaciers move over Earth’s surface, the ice acts like sandpaper, picking up and carrying away rock material, scraping the ground underneath it.

. Striations are the scratch marks that are visible when the ice melts.

Gravity

Eric Hamber Secondary 15 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre . When rain soaks the slopes of a steep hill or mountain, the soil and rock material become heavy and unable to resist the force of gravity.

. The result is a large part of the hillside or mountainside falling away and sliding downward (landslide)

. An avalanche is a landslide of ice and snow.

Deposition by Water and Ice

. Moving water and glaciers not only erode the land they travel over, they also deposit the materials they pick up.

. When fast-moving river water enters a body of water, it slows down and begins to drop the sediments it has carried downstream.

. When this happens in the place where a river enters a lake or ocean, the deposits form a fan-shape called a delta.

Eric Hamber Secondary 16 Chapter 10 – The Water Cycle Plays a Vital Role on Earth Learning Strategies Centre