Distribuution and geomorphic significance of mountain permafrost in the Japanese Alps

通过野外地温监测和指示多年冻土条件的岩石冰川地形分析，估计了日本阿尔卑斯山两个地区的山地多年冻土分布。还进行了实地观测，试图评估与山区永久冻土有关的当代地貌过程。这项为期两年的研究得出了以下结论：1.热观测表明，日本阿尔卑斯山北部库拉诺苏克环带的岩石冰川被永久冻土覆盖，因此，该岩石冰川尚未形成化石。在日本阿尔卑斯山南部Ainodake地区海拔3000米以上的北面岩壁中也可能存在永久冻土。2.地形分析表明，以前被确认为晚冰川的地貌实际上是残留的岩石冰川，这表明过去的永久冻土环境普遍存在于日本阿尔卑斯山。这些岩石冰川具有分叶或舌形、脊沟地貌、最外脊最高和顶面下陷的特征，这些都是在瑞士阿尔卑斯山典型的岩石冰川化石中观察到的。3.从时间尺度上提出了三种不同的冻融旋回。它们是日周期、年度周期和千年周期。永久冻土的存在很少影响白天的冻融作用，但对于控制每年发生的坡度过程是必不可少的。第三类是千禧年冻融作用，它直接反映了多年冻土的消长，可能产生了包括悬崖瀑布和陡峭山坡上的泥石流在内的大规模地貌变化。最近的全球变暖使人们注意到未来对千禧年周期解冻阶段产生的自然灾害的预测。

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.