Table 6. Extreme predicted perma-
The permafrost reaches a thickness of 2132 m after 1 million
years and a value of 2255 m after 2 million years. Balobaev et al.
(1978) note that the greatest permafrost thicknesses recorded are on
the East Siberian platform and present graphs with maximum perma-
U = 1 mm/yr
frost thicknesses of 1500 m. These thicknesses are on the order of the
value predicted here and it is not likely permafrost much thicker than
this has ever existed, since the required time exceeds the plausible
time available. These extreme thicknesses are not in thermal equilib-
rium with the present surface temperatures and are slowly thawing.
The calculations and examples indicate that the growth of permafrost, with pure conduction heat trans-
fer, is governed by the transient surface temperature, the geothermal heat flow and the soil thermal proper-
ties. Permafrost grows very rapidly for an initial phase and then asymptotically approaches a steady-state
value after time spans of immense length. Very thick permafrost may have required the total Quaternary
Period to form. It is likely that permafrost is not in equilibrium at most sites. The bottom growth and decay
of permafrost are so slow that accurate methods of detecting which is occurring (or if equilibrium exists)
are not available for the field. Permafrost less than 600 m can grow within 50,000 years, with surface tem-
peratures only slightly lower than present values, but deeper permafrost depths require time scales of sever-
al ice ages and quite low temperatures to form.
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