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
Victor Diamond Mine crater facies and hypabyssal facies, and is considered to have a highly variable diamond grade. It is an open-pit mine; the equipment there is 100 tonne trucks, large front-end loaders, bulldozers and other necessary support equipment used in the mining operation. The annual production rate is 2.7 million tonnes a year, which comes to about 600,000 carats a year in diamond grade. There is year-round access via air travel and only seasonal access over land depending on whether the weather permits travel. On the property are warehouses for storage, a processing plant, workshops, offices, fuel storage facilities, pit-dewatering machinery and