The excessively cold temperatures also affect the geography of the tundra.

Landforms

In the Arctic tundra, the water trapped in the top layer of soil does strange things to the landscape. The water freezes each winter, and the ice melts each summer. When water freezes, it expands (takes up more space). When ice melts, it contracts (shrinks). This yearly expansion and contraction cracks and breaks rocks and creates hills, valleys, and other physical features.

A pingo is a small circular or oval hill formed when a pool of water under the ground freezes and forces the soil up and out. The hill may grow a few inches taller every year. Some pingos are as high as 300 feet (90 meters) and more than half a mile (800 meters) wide. Stone circles are formed by piles of rocks that have been moved into a more or less circular...