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
Merlin diamond mine which explored the possibility of reopening it . Striker has since become North Australian Diamonds , a company which operated the mine for a short period in 2006. Rio Tinto originally acquired the mining lease after a takeover of Ashton mining (November 2000) in which it also gained full control of the Argyle diamond mine. Ashton mining initially developed and operated the mine. Merlin diamond mine The Merlin diamond mine is one of only three diamond mines in Australia. The mine is located in the Northern Territory of Australia, about 80 kilometres south of Borroloola. The mine operated for a