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
Diamond mining in India was initiated during the rule of Chhatrasal, the Bundela ruler.. Diamond mining has continued in Panna region. As of 2017, there was one industrial-scale diamond mine in India, the Majhgawan mine, near the town of Panna, Madhya Pradesh. The deposit is in a kimberlite or lamproite pipe 6.5 ha in area, and yields 10 carats to the ton. Mining is done by an open pit, which was 85 m deep as of 2011. Exploration drilling has established that the pipe continues down to at least 330 m. The mine is owned by the National Mineral Development Corporation (NMDC), employs 199