Coletta M. Exler, age 11, of Pittsburgh, Pennsylvania, for her question:

Why are Hawaiian beaches covered with black sand?

The Hawaiian Islands are the tops of monstrous volcanoes whose feet stand miles blow on the floor of the Pacific Ocean. Eruptions began millions of years ago. Lavas and volcanic ashes heaped higher and higher until at last the islands poked their heads above the waves. Some of the volcanoes still erupt, adding lava and more gritty black volcanic ash to the islands. Storms and showers pelt the high peaks with rain and streams dash down the steep slopes to the island shores. The water brings down gritty grains of dark volcanic lava and dumps it in layers on some of the beaches.

Some, but by no means all, Hawaiian beaches are covered with this blackish, volcanic sand. The warm, gentle coastal waters happen to be just right for little coral sea creatures. These busy polyps build their graceful apartment houses of hard, stony coral. There are massive layers of this coral around the shores. The waves and the surf pound it to fragments and many Hawaiian breaches are covered with sand of glistening white . coral.