Esmeralda Rodriguez, age 11, of Scotts Mill, Ore., for her question:

WHAT CAUSES A TORNADO?

A tornado usually lasts less than an hour and will travel about 20 miles during its life, moving along at between 10 to 25 miles per hour. They've been known to last several hours and can move as far as 200 miles, spreading destruction and often death, as they travel from one place to another.

A tornado is a wind storm with a violent swirling of air that twists at speeds of more than 300: miles per hour. Some people call them twisters or cyclones. The storm is actually a rotating funnel cloud that extends from the cloud and often dips to the ground below. Tornados strike mostly in the Midwest states and those¬that stretch along the Gulf of Mexico.

The storms usually form along a front between dry, cool air that moves down from the north and hits humid, warm air that is moving up from the Gulf of Mexico. As the air rises, clouds develop and a squall line is produced. As the warm, dry air rises, more warm air rushes in and often it starts to rotate. It is this rotation that often develops into a tornado.

You'll find most tornados strike on hot, humid spring afternoons or early in the evenings. First there's a thunderstorm. clouds become dark and dense. Soon lower portions of the cloud mass start to twist and a funnel starts to extend downward. Hail and rain usually pelt down heavily and lightning can be seen. Then, often, there's a hissing sound as the twisting column of clouds extends toward the ground, often touching and picking up dirt and anything in its path.

With swirling air moving 300 miles an hour, there's a roar  and usually destruction of anything that is in the storm's path. With tremendous force, buildings can buckle and farms and gardens can be destroyed.

The uprooting forces of tornados result from the powerful updrafts of air inside the funnels. Tornados can uproot huge trees, lift railroad cars off tracks and move heavy objects.

People living in tornado areas learn how to behave when a storm warning is given. Many homes have storm cellars or basements. If caught outside, people lie face down in trenches or ravines. About 700 tornados are reported in the United States each year, but fortunately all of them do not take a heavy toll of life and property. The worst tornado ever recorded struck in a band across Missouri, Illinois and Indiana on March 18, 1928. The storm, moving at speeds of 60 miles an hour, killed 689 people.