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