Stanley Kushnir, aged 12, of Toronto, Canada for his question:

What causes a whirlpool?

You have seen a small ‑whirlpool in a wash basin: This happens sometimes when the water is trying to run down the drain. You can improve this little whirlpool. Use your hand to swirl the water around the rim of the basin. This speeds up the current of the water trying to escape through the small hole into the drain.

Actually the water cannot drain away fast enough. Some has to wait its turn. So it piles up in a funnel shape ‑ with a hole in the middle. Sometimes the hole in the middle is quite steep. You wonder how water can stand up in steep walls without support. Of course, it is rapidly moving water. Calm grater could never stand up in seep walls.

All whirlpools are rapidly moving water. A moving stream will flow smoothly down an even slope. But suppose the stream bed is littered with steep boulders. The running water keeps bumping into firm opposition. It smacks into a. rock and is turned back, The main stream catches it and swirls it forward again.

A little eddy, or whirlpool, forma behind the obstinate boulder. There may be pebbles on the stream bed below the whirlpool. In time the swirling water will grind them around to dig a deep hole.

Shooting the rapids in a stream of this sort is no easy job. The trick is to follow the main current as it weaves and twists to dodge the boulders. Avoid the eddies and whirlpools of churning white water.

One of the most famous of whirlpools is off the coast of Norway in the Arctic Sea, It is called the Maelstrom ‑ a name often used to describe any kind of confusing mixup. It means a churning, or grinding stream. The great Maelstrom off Norway is caused by opposing tides. At certain times of the day a vast current of water meets tap with another vast current of water moving in the opposite direction.

The two tides brush sides and pull each other into a swirling funnel ‑ or vortex. The mouth of the vortex is a mass of frothing foam. The sides are steep walls of swirling water. And the raging water howls like water howls like thunder.

This maelstrom abates with the tides. But the torrent of Niagara, produces a whirlpool that never slackens. Some distance down from the falls, the mighty current is opposed by the steep banks of the river. It swirls around to form a frothy pool above a deep bed of grinding stones ‑ a maelstrom