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
Mining in Western Australia worlds supply, which is, however, only one percent of the mines overall production. Apart from Argyle, there is only one other operating diamond mine in the state, the Ellendale mine, located 100 km east of Derby, which opened in 2002. Ellendale produces the rare yellow diamonds. In 2009, sale volumes for diamonds fell by 44 percent while the value of the industry in the state decreased by 53 percent in comparison to 2008. Eighty percent of all salt produced in Australia comes from Western Australia. Of the state's production, 77 percent, in turn, originates from Dampier Salt Limited's operations at