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
Letlhakane diamond mine at a processing plant at its sister mine, Orapa diamond mine, about distant. The Letlhakane mine is also managed from the Orapa mine. In 2015, over 2.1 million tons per year of ore was mined, and over 2.3 million tons was treated, resulting in 583,000 carats of diamond. As of 2017, the Letlhakane Mine ceased open pit operations and completed a plant for the processing of tailings. This is expected to extend the life of the operations at this facility until 2043. Letlhakane diamond mine The Letlhakane diamond mine is a diamond mine located in Botswana about west of the