Rock glaciers, Disko Island, Greenland, Version 1

Disko Island (8600 km2) is situated west of centralmainland Greenland. The island is part of the Tertiary volcanic province of West Greenland and is mainly made up by lavas. The landscape is a plateau basalt landscape with cirque carved lava plateaus and U-shaped valleys and fjords. Rock glaciers are frequent in Disko Island (Humlum, 1982). In southern Disko Island, about 60 km SSE of the two study sites, meteorological observations have been carried out since 1923 in the village of Godhavn. The present (1961-1990) mean annual air temperature is -3.9 C, the coldest month is March (-15.1 C), and July is the warmest month (7.1 C). The mean annual precipitation at Godhavn is about 400 mm water equivalent. Most of the precipitation (75 %) usually falls during the period June to December, associated with advection of moist, maritime air masses from the south and southwest along the Davis Strait. The remaining part of the year is comparatively dry, as it is dominated by cold and dry katabatic air masses flowing off the Greenland Ice Sheet to the east. Approximately 60-70 % of the mean annual precipitation is snow and in Godhavn a persistent snow cover is registered from late September to late May.

No systematic mapping of permafrost or permafrost related terrain features have been carried out in this part of West Greenland. Weidick (1968), however, places Disko Island within the zone of continuous permafrost. This is supported by the occurrence of open system pingos (Christiansen, 1995) and numerous rock glaciers (Humlum, 1982, 1984, 1988a, 1988b, 1996; Humlum et al., 1995; Rasch et al. 1996), which are geomorphic indications of the presence of widespread permafrost in Disko Island. Adopting a standard continental geothermal gradient of about 0.033 C m-1, the mean annual air temperature of -7.5 C (1991-96) indicates a potential permafrost thickness of about 175-225 m. This estimate is presumably somewhat conservative, as the Little Ice Age annual air temperature presumably was about 2C below modern values (Humlum, 1996), which would provide conditions for a somewhat thicker permafrost layer than is suggested by modern meteorological values. The high frequency of rock glaciers on Disko Island is presumably derived from high rock weathering rates (Humlum, 1992). These data are presented on the CAPS Version 1.0 CD-ROM, June
1998.

迪斯科岛（Disko Island）面积8600平方千米，坐落于格陵兰中部大陆以西。该岛隶属于西格陵兰第三纪火山省，主体由熔岩构成。其地貌为高原玄武岩地貌，发育有冰斗侵蚀形成的熔岩高原、U型谷与峡湾。岩冰川（rock glacier）在迪斯科岛上分布广泛（Humlum，1982）。
在迪斯科岛南部，距两处研究点东南方向约60千米处的戈特哈文（Godhavn）村，自1923年起便开展了气象观测工作。1961-1990年时段的年平均气温为-3.9℃，最冷月份为3月（-15.1℃），最热月份为7月（7.1℃）。戈特哈文的年平均降水量约为400毫米水当量，其中75%的降水集中于6月至12月，这与沿戴维斯海峡（Davis Strait）从南、西南方向输送而来的湿润海洋气团平流作用密切相关。一年中其余时段气候相对干燥，此时主导气团为从格陵兰冰盖（Greenland Ice Sheet）向东流动的寒冷干燥下降冷气团（katabatic air masses）。年平均降水中约60%-70%为降雪，戈特哈文地区的常年积雪期为9月下旬至次年5月下旬。
西格陵兰该区域尚未开展过永久冻土（permafrost）或永久冻土相关地貌特征的系统性测绘工作。但韦德克（Weidick，1968）将迪斯科岛划入连续永久冻土带范畴。这一结论得到了开放系统冰核丘（pingo）的出现以及大量岩冰川（Humlum，1982、1984、1988a、1988b、1996；Humlum等，1995；Rasch等，1996）的佐证，这些地貌均为迪斯科岛广泛分布永久冻土的指示标志。采用约0.033℃/米的标准大陆地热梯度，结合1991-1996年-7.5℃的年平均气温，可推算出潜在永久冻土厚度约为175-225米。该估算值或偏保守，因为小冰期（Little Ice Age）的年平均气温较现代值低约2℃（Humlum，1996），这意味着当时的永久冻土厚度会比现代气象数据推算的结果更厚。迪斯科岛岩冰川分布广泛，或源于当地较高的岩石风化速率（Humlum，1992）。本数据集相关数据收录于1998年6月发布的CAPS 1.0版光盘中。