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
Argyle diamond mine over a period of 18 months at a cost of A$450 million. The mine was commissioned in December 1985. "Several of this article's references contain excellent maps and photographs of the mine and examples of diamonds produced there, which cannot be placed in this article due to copyright limitations. The reader is especially directed to Shigley, Chapman, and Ellison's article, "Discovery and Mining of the Argyle Diamond Deposit, Australia" (Gems & Gemology, Spring 2001)." Argyle diamond mine The Argyle Diamond Mine is a diamond mine located in the East Kimberley region in the remote north of Western Australia. Argyle is