According to the International Permafrost Association, permafrost is ground (soil or rock and included ice or organic material) that remains at or below 0°C for at least two consecutive years. Permafrost can extend to depths of more than 1500 meters.
Most permafrost is located at high latitudes (close to the North and South poles), but alpine permafrost may exist in mountainous regions at high elevations much closer to the equator. Permafrost underlies 20-25% of Earth's land area. Almost half of Canada, including most of the North and some of the mountainous parts of southern Canada, is underlain by permafrost.