Monique Boulais, age 11, of Montreal, P. Q. , for her question:

 How is a crater formed?

A crater is a hole in the ground, usually a round, wide hole with steep sides and a flat floor. A few craters were punched into the earth by fallen meteorites. Once in a very great while, a large lump of rock comes hurtling through the skies. It is a meteor until it hits the earth. Then it becomes a meteorite. A big fellow can plow deep into the ground, leaving a mile wide crater in its wake.

Most craters, however, come from below. They are the throats of volcanoes. A volcano has a deep vent, a weak spot in the earths crust, reaching maybe 30 miles below the surface. At its roots is a pool of magma, a reservoir of molten rock bubbling with gases. When the volcano erupts the magma rushes up the vent as lava.

The crater of an active volcano is usually full of small vents, always pouring forth smoke and steam. When the volcano dies, the crater becomes a calm, steep sided hollow cradled at the top of the volcano cone. It often fills with water and forms a blue crater lake high up among the clouds.