Beaver lodge and dam (Photo credit: Bemep)
One of the interesting things about the beaver is that its obsession with civil engineering may have a profound effect upon landscape. Before Europeans set foot in North America, it is estimated that up to 400 million of them inhabited the continent. The ponds that they create by building the dams in which they live securely, encourage sedimentation. It is quite possible that this creates recognisable stratigraphic formations; but no-one really knows as active and wet beaver habitats hide what lies beneath them. It is clearly urgent to obtain this intelligence: the Geological Society of America’s monthly Geology contained in its first issue for 2012 a paper that indeed probes the legacy of large rodents long gone (Kramer, N. et al. 2012. Using ground penetrating radar to ‘unearth’ buried beaver dams. Geology, v. 40, p. 43-46).
The target for surveillance was the eponymous Beaver Meadows in Colorado, USA, and not only did the researchers from Colorado State University deploy ground-penetrating radar, but used the seismic reflection method as well, to quantify volumes of beaver-induced sedimentation. Fortunately, despite their past presence in some strength, beavers no longer frequent Beaver Meadows and no ethical lines in the sand were crossed. Beaver and elk seemingly have long competed for the meagre resources of Beaver Meadows, the rodent having finally succumbed locally to determined efforts by the elk to consume the beavers’ victuals. As disconcerted and no doubt sulking beavers failed to maintain their dams and lodges, the water table fell, further encouraging the elk. Eventually, at some time after the Beaver Survey of 1947, the last of them moved to new meadows. Their ravages (see http://animal.discovery.com/videos/fooled-by-nature-beaver-dams.html) of what would otherwise be dense woodland have, however, made it possible for geophysicists to try out their sophisticated kit on a new and thorny issue: they ran 6 km of GPR and seismic profiles.
A beaver. Image via Wikipedia
In much the same way as larger scale geophysical data are interpreted for petroleum traps, signs of hydrocarbons, mighty listric faults and zones of tectonic inversion, the beaver-oriented sections potentially yield considerable insight to the trained eye. There are indeed beaverine sedimentary aggradations of Holocene age above the local glacial tills. Beneath Beaver Meadow they amount to as much as 50% of post-glacial sediment. Apparently, the deposits have a linear element that follows the local drainages.
Related articles
- How Beavers Helped to Build America (news.discovery.com)
- Are beavers dangerous? (greenanswers.com)
- READERS RESPOND: What should replace the beaver? (cbc.ca)
- Senator gnaws at beaver’s status as national symbol (ctv.ca)
- Will Canada dump the beaver? (gadling.com)
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It’s a very interesting study. Other geophysical techniques such as DC resistivity could be used as well. The penetration depth of GPR is limited and the data processing of seismic reflection are complicated. The reflection interface generally needs to deep to get “clean” data. Resistivity method could suit right between these two methods.