Friday, December 19, 2008
Mt. Cardigan, NH, glacially polished ledges below the summit, 2006
These photos taken on a ridge of Mt. Cardigan indicate how the White Mountains, some of them at least, might have looked in the years immediately after the glacier ablated. Their soil is thin because of a low level of weathering in the granite and gneiss rocks which are very hard and resistant to weathering. The high rate of sheet flow, as in water runoff, too, would have impeded weathering, but, like on Zeacliff, the bald caps eventually manage to foster spotty soil in thin layers followed by a cap of vegetation, usually coniferous, like balsam, along with black and red spruce. In these photos there is a glimpse of what some of the mountains looked like 8 or 9,000 years ago meaning they were polished to some extent, capturing soil in small cracks in the hard rock that started as sand and gravel from wind borne particles, frost action and local erosion. These unlikely niches are then colonized by a few pioneering conifers and perhaps some dwarf birch or other shade intolerant species like Mountain Ash. It makes sense that forest followed the melting glacier almost instantly. It’s feasible that trees were growing within 5 to 20 years in some favorable places as the glacier melted nearby. The limiting factors, again, would be temperature and amount of sunlight and their affect on photosynthesis and seed germination.