The region is largely rocky desert with an average altitude of more than 900 metres (2,953 feet) above sea level. The highest peak is at 3,003 metres (Mount Tahat). The mountain range is chiefly volcanic rock and contains a hot summer climate, with a cold winter climate (temperatures fall below 0°C in the winter). The mountains are young at about 2 million years old and rainfall is sporadic. However, since the climate is less extreme than in most other areas of the Sahara, the Hoggar Mountains are a major location for biodiversity.