A couple of days ago news broke of another Alberta first: a beaver dam 1/2 a mile in length, about 190 klicks NNE of Fort McMurray, just inside Wood Buffalo National Park.
The damn was spotted by researcher Jean Thie when he was playing around with Google Earth in an attempt to determine the effects of Global Warming on Northern Canada's permafrost layer.
Well, it turns out the dam has its own website, courtesy of Mr. Thie, with a whacka whacka good information on beaver habitats in general and this dam in particular. Above is a Google Earth image of the structure, and here is some background:
This dam was measured with the Google Earth Measuring tool to be about 850 meters in length. It has clearly two or more lodges and is a combination of two original dams. No surface water drainage can be seen. Water moves down the very slight sloping wetland. The ( relative thin layer) of organic material of the wetland works as a sponge . The flow is slow and over a wide area of wetland which requires the building of very long dams. Many dams can be found in areas like this with lengths of 500 meters. Any dam over 600 meter remains exceptional.
I emailed Mr. Thie wondering if the growth of the dam (it appears to have existed in a smaller form as far back as 1990) might somehow be attributed to AGW related permafrost melts releasing extra water over the years. He was kind enough to send the following response:
Thanks for your interest and careful reading. No, I do not think that the size of the dam is related to global warming. In the first place the water supply for the wetland comes from the creeks and streams coming down from the Birch Mountains, not from melting permafrost.
Second,this area has only sporadic and isolated patches of permafrost, usually in the form of palsas and peatplateuas in wetlands ( an example : http://www.geostrategis.com/p_mapm2.htm ). Pemafrost in wetlands in this area was formed after the last glaciation and after the the layers of peat were formed.
This area was burned about (probably a number of times) 20-40 years before 1975 when the black and white aerial photo was taken. The "Poplar Island" is most likely a fire regeneration. Poplar of course is a favourate food for beaver and as you can see on the Google Earth image beavers have build a small dam here.
This link gives you a bit of background on understanding fire history in the boreal zone http://www.geostrategis.com/p_borealfires.htm
So there you have it. Follow the links to see more clearly what Mr. Thie is talking about.