Permafrost by permafrost. Of this area slightly more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, and a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost typically forms in any climate where the mean annual air temperature is less than the
Orapa diamond mine Orapa diamond mine The Orapa diamond mine is the world's largest diamond mine by area. The mine is located in Orapa, a town in the Central District of Botswana about west of the city of Francistown. Orapa ("resting place for lions") is owned by Debswana, a partnership between the De Beers company and the government of Botswana. It is the oldest of four mines operated by the company, having begun operations in July 1971. Orapa is an open pit style of mine and is the largest diamond mine in the world by area. The mine is located on two kimberlite