The process by which earth's plates slowly move across the upper mantle.

Areas of the ocean floor where rocks gradually sink because they have no supporting heat below them; the world's flattest and smoothest regions.

Small particles of weathered rock.

An elevated flatland that rises sharply above nearby land on at least one side.

Accumulation of sediment at the mouth of a river.

First and smallest streams formed from the runoff of a mountain, eventually forming rivers.

The entire region drained by a river and its tributaries.

Landscapes that are covered with water for at least part of the year.

Water found below ground.

Broken-down plant and animal matter in soil.

The practice of planting different crops in a field in alternating years.

A process in which water is artificially supplied to the land.

Groundwater that is not replenished by rain.

Energy resources-formed from the remains of ancient plants and animals- including coal, natural gas, and petroleum.