The 40th edition of the photo of the week highlights the mudlfow from a retrogressive thaw slump near Fort McPherson in the Northwest Territories, where I did field work for a few weeks in 2010 and 2011.

The first photo in this series highlights the slump itself. I took this photo from a helicopter and the entire slump is approximately 1 kilometer wide and has 3 lobes. The mudflow starts where everything converges. I have been told by people who have been back that the slump does not look anything like this today and it is approximately 30-50% larger!

The next photo shows the convergence point in the top right and the start of the mudflow as it moves down the valley. There is so much mud that the little stream that once flowed in the valley has been completely dammed and formed a lake.

The final photo in the series shows the rest of the mudflow, which extends for about 10 kilometres down the valley.