tectonic plates Immense portions of the lithosphere that slide over the asthenosphere; this shifting movement shapes the Earth’s topography.
mountain Elevated landform characterized by steep slopes; it is usually part of a chain.
glacier Mass of ice resulting from the accumulation and compression of snow; it moves under its own weight.
cave Natural underground cavity that results from the slow dissolution and erosion of rock by water.
landslides Ground movements that vary in speed, depending on the slope’s gradient, the nature of the soil and what triggers it.
watercourse Natural flow of water that varies in size, depending on the ground slope and the number of tributaries.
lakes Bodies of water varying in size and completely surrounded by land.
wave Undulation caused by the wind on the surface of a sea or lake.
ocean floor Part of the Earth’s surface beneath the seas and the oceans; its topography is highly variable.
ocean trenches and ridges Trench: very deep, elongated cavity bordering a continent or an island arc; it forms when one tectonic plate slides beneath another. Ridge: underwater mountain range that criss-crosses the oceans and is formed by rising magma in a zone where two plates are moving apart.
earthquake Sudden tremor in a region of the Earth’s crust caused by one rock mass sliding against another.