Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 21

At the bottom of the ocean is a landscape that’s as varied as what you see above the ocean, complete with plains, ridges (mountain ranges), seamounts (mountains), hills, canyons, trenches (valleys), cliffs, volcanoes, hydrothermal vents (underwater geysers), and even rivers and massive “waterfalls” of sand and sediment that you do indeed want to go chasing.

The shape of the ocean floor (as well as all land) is largely determined by a process called plate tectonics — the bumping, grinding, and separating of tectonic plates (massive sections of rock that form Earth’s crust). These plates ride atop a semi-liquid layer of molten rock (imagine heating a rock till it melts — that’s HOT). Convection currents in the molten rock move the plates at three to five centimeters (one to two inches) per year. (See Chapter 6 for more about plate tectonics.)

Plate tectonics are also responsible for creating most tsunamis. Whenever land shifts at the bottom of the ocean or an underwater volcano erupts, the resulting displacement of water can send a wave thousands of miles across the ocean in a matter of only a few hours. (See Chapter 16 for more about waves and tsunamis.)