Volcanic craters cover the landscape in Harrat Khaybar, a lava field in Saudi Arabia. Formed by a series of eruptions over 5 million years, the Harrat covers an area of more than 4,600 square miles (12,000 square km). In the bottom right of this Overview is White Mountain, a geological rarity which gets its pale color from a huge volcanic explosion that emitted gases and white ash containing silicon.