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The
Water Cycle
The
water cycle is also known as the hydrologic cycle. The water
cycle moves water from any one of Earth's water storage areas, oceans,
lakes, or the atmosphere, to another. Basically, water moves from
the Earth to the atmosphere, and from the atmosphere back to the
Earth in a never ending cycle.
Water comes to Earth as precipitation in
the form of rain, sleet, or snow. A portion of the water soaks into
the ground through infiltration and becomes groundwater, while the
remainder flows as runoff into streams, lakes, rivers, and oceans.
Evaporation
Evaporation is the process that makes the
water cycle work.
The sun heats the Earth's suface water turning
the water into vapor. This is known as evaporation.
Water can evaporate from any body of water
such as rivers, lakes, streams, and oceans. Water is the only substance
on Earth that can change its form as solid, liquid, and gas naturally.
Water molecules are given energy as heat by the sun, which causes
evaporation process to occur.
Transpiration is the process where
plants give off water vapor. Water vapor that animals sweat and
breathe out (including humans) also evaporates and goes into the
atmosphere.
The heated water vapor rises into the atmosphere,
cools, and forms clouds. When the vapor cools it condenses and cohesion
pulls the molecules together into water drops. These tiny droplets
cling to dust particles to form larger droplets which then can fall
again as rain or snow. Condensation is the beginning of turning
water vapor back into liquid water.
When water evaporates, the salts and other
solids that had been in the water, are left behind.
Temperature plays a role in how much water can be
held in the vapor form in the cloud. The warmer it is, the more
water vapor a cloud can hold.
When the air temperature decreases the heavy water droplets are
pulled back to Earth by gravity in a process called precipitation.
Run Off
Precipitation can take the form of
rain, snow, or sleet. Sleet is a combination of rain and snow. Snow
and ice can collect on mountain tops, and stay there for years as
glaciers. When snow and glaciers melt in the mountains, the water
is released and pulled downward by gravity as runoff that flows
into streams and rivers.
Small creeks run into depressions in Earth's
surface and form lakes. Rivers then can flow from lakes, and eventually
flow directly into the ocean.
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