Vicki Parrish, age 12, of Burlington, N.C., for her question:

What is the mid Atlantic rise?

The face of our handsome planet is wrinkled with mountains and valleys, scarred with steep walled canyons and spotted with seething volcanoes. Most of our globe is covered with water, and the floors of the oceans also have their ups and downs, grooves and ridges.

We measure the ups and downs of the continents from sea level, which is the average level of the ocean surface between high and low tides. The sandy floor of Death Valley lies 281 feet below sea level, and the snowy shoulders of Mt. Everest rise 29,000 feet above sea level. But the deepest grooves and the most massive mountains of the solid surface of the Earth are below sea level. They are the ups and downs on the bumpy floors of the worldwide oceans.

The job of surveying the ocean floor began only a few years ago, and it is not yet completed. For a long time the experts had suspected that the floor of the Atlantic was far from smooth, but the discovery of the mid Atlantic rise came as a stupendous surprise. It was reasonable to suppose that Iceland, the Azores and other mid Atlantic isles might be the peaks of undersea mountains. But the facts revealed that these spots of dry land are the lofty peaks of a massive undersea ridge of mountains stretching from the Arctic to the Antarctic.

This mid Atlantic ridge now appears to be only part of a still more staggering system of undersea mountains. It is linked with a mid ocean ridge that snakes its way through all the great oceans of the world. The mid Atlantic ridge is some 10,000 miles long. The mid ocean ridge that wanders on through the Pacific, Antarctic and Indian Oceans has a total length of more than 40,000 miles.

The wide plains on the floor of the Atlantic basin are three miles below sea level. They are dotted with hills and flat topped mounts and pitted with cracks. About halfway across the basin floor begins to rise in terraced foothills. The rise continues until in mid Atlantic some of its peaks break the surface and become islands. The massive mountain range rests on a base that varies from 300 to 1,200 miles wide, and it occupies one third of the solid ground below the North and South Atlantic Oceans. It may be called the mid Atlantic rise, but most geographers call it the mid Atlantic ridge.

The east and west shores of the Atlantic snake along in more or less parallel lines. The great ridge in mid ocean follows these snaky curves. Its spine is cleft with a deep valley some 30 miles wide. This is the Atlantic rift, which cuts a deep gorge into the highest core of the meandering underwater range. There are similar rifts in other stretches of the mid ocean ridge, and in these unsettled areas of the Earth’s crust there are many submarine volcanoes and frequent underwater seaquakes.