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
Williamson diamond mine the future. The mine was equipped with a range of sporting facilities. These included public swimming pool, tennis and squash courts, soccer field, athletics track, golf course and yacht club. There was also a surgical hospital staffed by two English and an Indian doctor and nursing staff. The hospital used to treat the mine employees for free, and poor people from neighbouring areas could take treatment there at nominal charges. These facilities fell into disrepair after the colonial era, but remain partly maintained by the mine. Williamson diamond mine The Williamson Diamond Mine (also known as the Mwadui mine) is