Robert Showman, age 11, of Ottawa, Ont.

What causes geysers?

Geysers have their roots deep underground. They occur in old beds of volcanic lava. Sometimes the surface layer, cooled quickly after an eruption, leaving heat trapped in layers of rock below. When the surface layer cooled and hardened, it sealed in the heat below.

Rain falls and seeps down into the earth. It trickles through cracks and oozes through the pores of the surface lava. It collects as ground water among the hot layers of rock below,

The ground water becomes heated, boils and turns to steam. When the underground kettle boils over, it bursts up through a vent to the surface. The geyser spits up a plume of steam and hot water. Meantime, the kettle below is filling up with more ground water. It heats up, boils over and the geyser is ready to spit again.

Iceland is a land of geysers and hot springs. They are formed around the roots of smouldering volcanoes. The geysers of America's Yellowstone National Park are in a region of ancient volcanic activity.