Retrogressive Permafrost Thaw Slides

RETROGRESSIVE PERMAFROST THAW IN THE TREVOR RANGE YUKON - EXPLORING PERMAFROST MELTING WITH GOOGLE EARTH

An excellent selection of sites in the Yukon showing significant slides and regression of permafrost in mineral soils was made available on Google Earth by "kingpointnorth" in the original Google Earth Community Forum. At that time I did a significant amount of work studying the melting and regression rates of landslides in Northern Canada.

To do this I used as base data Aerial photography taken in the North since the mid 1920's. From the 1950's on aerial photography becomes a more dependable source of information for comparison.

Figure 1 below shows a glacier like retreat of land based permafrost. It is based on a comparison and interpretation of a series of aerial and satellite images. The left is an 1966 July Aerial photo (A19650-67) draped over a Google Earth. To the right is the Google Earth high resolution Digital Globe July 2004 image. The grey dotted lines show the permafrost melting/ erosion edge in 1966. The Yellow dotted line is derived from a NASA Landsat 1990 low resolution image interpretation (WorldWind) and the orange dotted line is represents the GE 2004 digital Globe image.






The maximum regression distance over the 38 year period is about 850 meters, while the active edge is close to 890 meters in length. Average regression rate would be in the order of 20 meters per year . Most of it, certainly volume wise, in the last 14 years. There are no indications that this slide has been triggered by wildland fires as there is no evidence of fire history on the aerial and satellite images.

This melting and regression rate is comparable to other rates documented in the Yukon. Form example Burn and Friele (1989 Arctic vol. 42 no.1, p31-40) measure regression rates of up to 16 meters per year in retrogressive thaw slumps near Mayo, Yukon Territory

more information at: www.geostrategis.com/p_permafrost-slides.htm





1107312-PermafrostThaw1966-2005TrevorRangeS....kmz (177.52 KB)

The Trevor Range Slide in 2015

The Google Earth image layer in this area has not changed in the last 7 years in this study area. Therefore I looked at alternative sources of high resolution imagery. Apple Maps provides now an excellent high resolution source for many areas in Northern Canada. The following image demonstrates that and shows the 'present' situation -around 2015

The movement of mud flows can easily be seen on the image in Figure 1. Recent ones are free of vegetation, older ones become progressively more invaded. 

FIG 1



The image below-figure 2- shows the overlay of the Apple Maps image over the 2004 Google Earth base. The pink line represents the melting edge in 2004, as mapped on the Google Earth Image. The retrogression of the edge is between 150 and 250 meters over 10 years. 
FIG 2



The regression rate over the last 10 years continues the trend since my earliest observation of 1966. The green line shows the melting edge in 2014.(Figure 3)
The small white patches are snow remnants from winter. The date of the GE images is 16 June, 2004.

FIG 3



The following attached KMZ file shows the Apple Maps overlay, which you can make more or less transparent to study the change area in detail

Attachments:

Permafrost slide Trevor Range 2004-2015.kmz (322.03 KB)

Google Earth provides of course quite an amazing view of the earth, and when you combine the terrain feature with sunlight/ shading you get a great '3D' visualization of the landscape. But that visualization is based on a digital terrain model which is quite crude. 

Aerial photos provide an great alternative method, and with their accurate representation of the relief of the landscape an effective tool to better understand ecosystem and land use relationships.

For the Trevor Range site, I made a quite a while ago a stereopair from two 1966 black and white aerial photos. See below.
You can of course print the image and use a stereoscope to see the an accurate 3D view of the landscape. But you also can do it (un)naturally with your eyes

 I challenge you to try this with this image on your computerscreen;
fuse the two images into one and be amazed by the depth perception- the landscape looks actually quite different than my images in the previous posts.

It is initially not so easy, because while focussing on the screen your eye axes naturally converge. To get the the 3D view you have keep your eye axes parallel. It takes a bit of time.

By the way, the red arrow points to the 1966 melting edge of the Thaw Slide. At that time it was still quite small. 




The image below uses the digital terrain model and the sunlight shading effect to create an impression of the 3D model, however, as you have seen, the stereopair above provides a much more effective view.

In the Trevor Range there are of course more retrogressive thaw slides. I have mapped a few around the original site described above on the satellite image below. 
A total of 12 sites. Most of these were identified on  Apple Maps sources since the Google Earth coverage does not provide a good resolution for this area.





Below is the Trevor Range Slide marked as 2




Below is the Google Earth 2004 image of Trevor Range Thaw slide no.3- a quite substantial slide as well.