The endokarstic erosion of marble in cold climates: Corbel revisited

摘要

After the work of Jean Corbel in the 1950s, who compared karstification in the Scandinavian Caledonide marbles with that in sedimentary limestones in temperate and tropical regions, the understanding of underground limestone dissolution has developed considerably. Corbel concluded that 'karstification proceeds much faster in a cold than in a warm climate', based on the knowledge that the solubilities of both CO2 and CaCO3 increase with lower temperature, without realizing that because cave streams in Scandinavia rarely reach saturation this fact is not directly relevant. We now know that the dissolutional enlargement of inception channels in limestones proceeds commonly via a slow initial 'pre-breakthrough' laminar flow stage before conduits can enlarge chemically at maximum rates under turbulent flow conditions. Recent research has shown that the pre-breakthrough stage is speeded up at low temperatures, as occurs in cold climates now, and as occurred during the deglaciation of the Weichselian ice sheet in Scandinavia, especially under steep hydraulic gradients and, in many cases, despite the lower partial pressure of CO2. Additionally, this whole stage might be bypassed if fractures created by deglacial seismicity were wide enough and short enough. After breakthrough, although limestone dissolution is slower in cold rather than warm climates, conduit enlargement still proceeds at a significant rate, provided the water remains unsaturated, and especially if high flow rates promote mechanical erosion. The exploration of large numbers of (short) caves in central Scandinavia shows that Corbel's conclusion is partly true for the more recent geological past, because of the special conditions that apply during the Quaternary glacial cycles.