Weathering and erosion

Over the millions of years of geological time, great mountain ranges have been forced up—then disappeared. Colliding tectonic plates, faulting and other earth movements have...

Slopes and landslides

Slopes are unstable because gravity causes material such as soil, mud, rock fragments and rock itself to creep, slide, flow or fall down them. The presence of water is an important...

Escarpments and cuestas

An escarpment (or scarp) is a steep slope or long cliff that forms as a result of faulting or erosion—where it marks the boundary between harder and softer layers of rock. A...

Rivers

Rivers are natural channels that carry rain, melted ice and snow downhill from mountains and uplands to lowlands, lakes and seas. The world’s longest rivers are the Nile in...

Grand Canyon

The Grand Canyon is a great gorge that twists across the dry, rocky region of Arizona, USA for nearly 450 kilometres (280 miles). It is one of the world’s most spectacular...

Rivers A-Z

Caves

Caves are underground holes in the rock. Some caves open up when the ground splits, as in an earthquake. Some are eroded by waves hurling stones and pebbles at a cliff. But most...

Limestone landscapes

Limestone, a type of sedimentary rock, consists of the remains of tiny sea creatures that lived millions of years ago. It is made of calcium carbonate, a substance that dissolves...

Coastlines

Coastlines are where ocean or sea meets land. Some coastlines are shaped by the action of waves crashing against them, wearing away the rocks. Along others, sand and shingle are...

Coastlines A-Z

Deserts

A desert is an area with very low rainfall, usually with less than 25 centimetres (10 inches) of rain or snow a year. Other than at oases, places where underground water comes to...

Deserts A-Z

Glaciers

A glacier is a moving mass of ice. Some glaciers snake down mountain valleys, while others such as the ice sheets of Greenland or Antarctica are so huge and thick they almost...

Ice age glaciation

Ice ages are times when the climate cools down so much that ice sheets form at the poles and in mountainous areas and spread out. The most recent ice age began around 2.6 million...

Glaciers A-Z