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CN: Water Cycle Continuous Process process by which water moves through the living and nonliving parts of the environment. Sun The sun provides energy to power the water cycle Without it the water cycle would stop Chapter 11 Section 1 The Active River Water Cycle Click below to watch the Visual Concept. Visual Concept Water on the Earth Chemical Formula: H2O Almost all the water on Earth is salt water (97%). The other 3% is fresh water 76% of thatis frozen in the ice caps at the poles. Much of the remaining is groundwater. Evaporation Most important process in the water cycle Happens when the SUN heats up the water in rivers, lakes, and oceans and turns it into a gas (vapor or steam) and it goes into the atmosphere. Most of the water vapor that evaporates into the air comes from the oceans. The salt does not get enough energy to become a gas, so it stays behind. So rain is always fresh water! Condensation 2nd most important process in the water cycle Dew is formed by condensation of water vapor Takes place in the atmosphere The stage where gas turns into a liquid Clouds Water vapor cools as it rises in the air. As it reaches the dew point, the water vapor will condense around dust particles and form clouds. Precipitation Condensed water vapor that gets heavy enough to fall to the ground as rain, snow, sleet, or hail. Most water molecules only spend about ten days in the air before falling back as precipitation. Surface Runoff Much of the precipitation runs off the surface and flows downhill into streams. These flow into larger streams, then rivers, and eventually flow back into the ocean. Infiltration Infiltration is an important process where rain water soaks into the ground, through the soil and underlying rock layers. Some of this water ultimately returns to the surface at springs or in low spots downhill. Percolation Percolation is when water after it rains seeps into the ground and is stored there, thus becoming ground water Groundwater Some precipitated water that does not flow into rivers, lakes, etc sinks into the ground (permeable) and eventually reaches a layer it cannot pass through (impermeable). Most of the fresh water that is not frozen is underground. Groundwater As the water infiltrates through the soil and rock layers, many of the impurities in the water are filtered out. This filtering process helps clean the water. The amount of groundwater stored is dependent on the porosity of the rock (like pores on your skin) Transpiration As plants absorb water from the t soil, the water moves from the roots through the stems to the leaves. Once the water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapor in the air. The greatest living movers of water are plants. Where would you have more moisture (water vapor)….desert or forest? Why? Aquifer An underground bed or layer of permeable rock, sediment, or soil that yields water. Confined: permeable rock units that are usually deep under the ground and are under relatively impermeable rock or clay that limits groundwater movement into, or out of it Unconfined: groundwater is in direct contact with the atmosphere through the open pore spaces of the overlying soil or rock Water Table the level below which the ground is saturated with water. The “line” at the top of an UNCONFINED aquifer When you start digging in a field (fairly deep) and you start to see water, you are at the water table Artesian Well a pumpless water source that uses pipes to allow underground water that is under pressure to rise to the surface. This type of well seems to defy gravity because the pressure that builds up between layers of rock gets relieved when the water finds a path to the open air. In addition, the water has been naturally filtered because it passes through porous rock as it seeps into the Earth to reach the aquifer, which is the underground water source. For centuries, people have drilled artesian wells to drink filtered water that doesn't need to be manually or mechanically hauled up from the depths. Conclusion: Earth’s Water Supply The total amount of water on the Earth has not changed much since early in its history. The same water is cycled over and over. The water you drink at lunch was probably drunk by a dinosaur millions of years ago! Water Distribution