Certain natural phenomena can be either harnessed or advantageously simulated to produce usable energy and fresh water from seawater. One such possibility is to utilize the huge reservoirs of energy buried deep under the surface of the earth, known as geothermal energy. This is, for example, manifested during volcanic eruptions when molten lava is emitted. Geysers, hot springs and fumaroles are also displays of geothermal energy. As far as desalination is concerned, the choice of using geothermal energy must depend on how far it would be competitive with other sources of energy. Moreover, the location of geothermal energy resources as well as saline water resources must play an important role in the selection of desalination processes. If the two types of resources are remote from each other, then conversion of geothermal energy to electrical energy and use of processes like RO, ED and mechanical VC would be preferable. If both resources are conveniently located close enough to each other, then MSF or MEB would be suitable. These aspects are discussed in more detail (See: Geothermal Energy and Desalination -Encyclopedia of Desalination and Water Resources ). The world's weather systems are driven by enormous amounts of solar energy. During summer in the tropics, patches of surface water are exposed to intense solar radiation. As these patches randomly migrate, the earth's rotation and drag of the atmosphere transform them into vortices. Then a tropical storm develops and rolls them up into a tight powerful vortex called a hurricane. As pointed out by hydrodynamicists, a hurricane-like vortex produces another vortex at right angles which carries moist air from the free surface up the sides of the rotating vortex to the top of the hurricane. There it is deflected by the cold of the upper atmosphere, condenses the vapor into water droplets which then fall as fresh water. As reported by Craven and Sullivan (1998), preparations are underway to simulate the above natural phenomena by building a hurricane tower in Hawaii. This will have a rotor spinning with a peripheral velocity of 100 mph simulating the hurricane vortex. Solar heated surface water will simulate the surface of the sea and a condensing plate cooled with deep ocean water simulates a cloud of ice. Another very promising initiative is currently under development in Israel. This is known as an energy tower, and it is a very large structure designed to harness solar energy but without using a collector, and therefore achieving much greater cost effectiveness. Energy towers could be built in the zones of the world where temperatures are highest, such as North Africa and the Middle East, They are very large vertical tubular columns, 1.2 km high and 400 m wide. Air is cooled by a spray of water at the top of the tower, causing it to become much denser and thus fall down the tower. A continuous downdraft, drawn in from a radius of up to 20 km, operating 24 hours per day, would drive a series of turbines at the bottom of the tower, generating electricity. If the energy tower is located next to the sea, it would also be possible to produce fresh water by desalination of seawater for about two-thirds of the present energy outlay.

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