Jamie Workman, age 11, of High Point, North Carolina, for her question:
What makes the ocean move?
Liquid water is unable to stand on its own feet. To stay in one place, it needs the support of solid walls and a solid floor. Otherwise the force of gravity pulls the runny substance down to the lowest level. This level is the enormous global ocean, into which the rivers flow. But even the oceans have the restless, movable qualities of all liquid substances. A slight breeze can ruffle their waves and much stronger forces are exerted to keep them in a state of upheaval.
We live on a watery planet and the oceans cover about 70 per cent of its surface. They are exposed to a variety of mighty forces from within the planet, from the atmosphere above it, and even cosmic forces from space. These same forces, of course, are also exerted on the solid land. But the liquid oceans have less strength to resist them. Afresh breeze of 20 miles per hour cannot budge a solid boulder. But it can whip up crested waves on the >urface of a lake.
The surface of the sea is calm only when the lazy breezes blow at less than one mile per hour. Most of its wave motions are caused by huffing and puffing winds ¬and when one area is disturbed, the ocean carries the motion on and on. Typhoon winds often start waves that break on the far side of the Pacific, halfway around the world.
The spinning earth directs the prevailing winds in belts around the globe. This effect is repeated in the motions of global ocean currents. But these currents are modified where the solid continents force them to change course. They also are modified by temperature. Warm tropical currents conflict with polar currents. Strange effects of pressure and temperature set in motion other currents in the deep ocean.
Every disturbance ca the seabed also starts upheavals in the watery ocean. A major seaquake may move billions of tons of water, starting a disastrous tsunami wave on its way to bash a beach thousands of miles away.
Meantime, out in space the gravity of the moon exerts a mighty pull or. our entire planet. As it passes overhead, it creates slight, though measurable, disturbances in the solid land. In the restless, watery oceans it creates tides that chase each other around the globe, heaving all the ocean waters up and down, twice in every 24 hour period. The high and low lunar tides wash up and down on every shore. They even lift and lower the water way out there in the middle of the vast oceans.
The rotating earth and the winds, the sun and the moon all conspire to disturb the oceans and the restless water carries these motions far and wide. But all this upheaval is good for the world. It mixes and merges warm and cool, salty and fresher waters in a constant global circulation. It washes the beaches, moderates the temperature of the land and shuttles around food supplies for the countless creatures that teem in the seas.