Chapter 4, Section 2 The Hydrosphere Focus questions: In what forms and where do we find water on Earth? What are the causes and effects of floods?

Water on Earth Water is one of our most important resources Humans can’t survive more than a week without it

Water is a valuable power resource Hydroelectricity - when water drives turbines to produce electricity

Water provides a valuable transportation network of rivers, lakes, and oceans

Characteristics of water… Water is the only substance on earth that exists as a liquid, a solid, or a gas in earth’s temperature range

Water has the ability to dissolve almost anything over time Water heats and cools very slowly Moderates the temperature on earth’s surface Winter, south coast of Iceland

Fresh water is unevenly distributed on earth’s surface

97% of water is in the oceans – unusable…why?

Seawater contains traces of every known element on earth Salts are the most common thing found in seawater Seawater is 3.5% salt – way too salty to drink

Desalinization (desalination) Very simple process boil the water, condense the steam back into water (minus the salt) Very expensive, uses lots of energy

2% of earth’s water is in the polar ice caps – unusable…why? North Pole 2% of earth’s water is in the polar ice caps – unusable…why? South Pole

Less than 1% of earth’s water is fresh (a.k.a. sweet) water Found in rivers, streams, lakes, and also undergound (groundwater) A small amount found in the atmosphere (clouds) and in plants & animals

Hydrologic (a.k.a. Water) Cycle The circulation of water through the hydrosphere Hydrosphere – all of the water on the planet Driven by solar energy

Step 1 – Evaporation Step 2 – Condensation Step 3 – Precipitation Most water in the atmosphere evaporates from the oceans Step 2 – Condensation As rising air cools, water vapor condenses into tiny droplets, which then form clouds Step 3 – Precipitation Rain, snow, etc.

Some precipitation falls as snow in mountains or polar areas

Some precipitation falls as rain and… flows off to rivers, streams, or lakes (called surface runoff) is absorbed into the ground, (called groundwater)

Surface water Headwaters Formed from runoff of precipitation down the slopes of hills and mountains The first and smallest streams to form from this runoff

Tributaries Any smaller streams or rivers that flow into a larger stream or river

Watershed (a.k.a. Drainage Basin) An area of land drained by a river and its tributaries

The Mississippi River Watershed covers over 1.2 million square miles

Lakes are formed when runoff fills a depression on the land surface Lakes form in different ways In depressions left by receding glaciers (ex. Great Lakes)

In Rift Valleys where continents are pulling apart (ex In Rift Valleys where continents are pulling apart (ex. Dead Sea between Israel and Jordan) The Dead Sea is so salty that you can float on your back and read a newspaper

An estuary may form where a river meets the sea A semi-enclosed body of fresh water and saltwater Rich in fish and shellfish

Wetlands are land areas that are flooded for at least part of the year Some of the earth’s most productive lands, with huge populations of fish, shellfish, and birds Also filters pollutants from the water

Groundwater Large freshwater resource beneath the surface of the land Comes from precipitation Water seeps down and collects in tiny spaces between rocks and soil

Top of the saturated zone is called the water table Water table may be near surface if climate is wet, or far below if climate is dry Wells must be drilled well below the water table to access this resource. Why? Well Water Table

Floods Occur when rivers carry more water than the channel can hold

Flooding is natural, but human activity can make floods worse Removing vegetation and paving over land speeds up surface runoff

Flood damage is often increased because people choose to live near rivers

Floodplains make good farmlands Why?

People have been trying to control floods for thousands of years, with some success The rivers always win in the end