Distribuution and geomorphic significance of mountain permafrost in the Japanese Alps

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The distribution of mountain permafrost was estimated in two regions of the Japanese Alps, by means of field monitoring of ground temperature and topographic analyzes of rock glaciers that indicate permafrost conditions. Field observations were also undertaken in an attempt to evaluate contemporary geomorphic processes associated with mountain permafrost. The two-year study led to the following conclusions.1.Thermal observations indicate that the rock glacier in the Kuranosuke cirque, northern Japanese Alps, is underlain by permafrost and, hence, the rock glacier has not yet been fossilized. Permafrost may also be present in the north-facing rockwalls above 3000m ASL in the Ainodake region, southern Japanese Alps.2.The topographic analysis demonstrates that large part of the landforms which have previously been identified as the Late Glacial moraines are, in fact, relict rock glaciers, suggesting the past permafrost environments widespread over Japanese Alps. These rock glaciers have the lobate or tongue-shaped form, ridge-furrow topography, highest outermost ridge and subsided top surface, all of which are observed on the typical fossilized rock glaciers in the Swiss Alps.3.Three kinds of freeze-thaw cycles are proposed in light of temporal scales. They are diurnal, annual and millennial cycles. The presence of permafrost rarely affects diurnal freeze-thaw action, but it is essential in controlling slope processes occurring at the annual basis. The third type, millennial freeze-thaw action, reflects directly the growth and decay of permafrost, possibly producing a large-scale gemorphic changes including cliff falls and debris flows on steep mountain slopes. Recent global warming gives attention to future predictions of natural hazards originating from the thawing phase of a millennial cycle.