EXPLORING PERMAFROST MELTING WITH GOOGLE EARTH:
RETROGRESSIVE PERMAFROST IN THE YUKON AND NORTHWEST TERRITORIES
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" (Google Earth BBS link). Although the sites are not described or documented, they provide an a good start for further study.
In the context of climate warming, it is interesting to look at some of these sites over a period of 50 years or more. Aerial photography has been 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. (See the National Air Photo Library on-line site)
I have taken a few if the sites and analyzed the information below from a time series perspective.SITE 1: Trevor Range, Yukon Territories, Canada (KML link)
This site is within the Peel River Plateau Ecoregion and the Taiga Plain Ecozone. The landscape is almost entirely shaped as result of the Laurentide glaciation, and post glacial fluvial and other geomorphological processes. Continuous permafrost is present with depth to base of ice-bearing permafrost close to 300m (Geological Survey of Canada, unpublished data). Retrogressive thaw flow slides are common where ground ice has been exposed in glaciolacustrine deposits by forest fires, debris flows and regressive erosion. (Ecoregions of the Yukon: Peel River Plateau).
Figure 1 below shows 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.
Figure 1 (larger version+)
The regression distance over the 38 year period is about close to 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 ar 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
Figure 2 Shows a stereo pair of the 1996 aerial photos of the site. The red arrow shows the start of the slide edge. It is interesting to note that the melting seems to follow the South-east sun facing slope.
Figure 3 shows the comparison of the 1990 and 2000 Landsat pseudo color images. The progression is clearly visible in the 10 year time period.
Figure 4 shows a very small scale winter satellite image of the surrounding landscape. Snow cover enhances the vegetation differences and densities.Bare snow covered areas are of course white. Light grey shades show sparse tree or shrub cover. The Trevor range site is identified with a yellow mark.
High Resolution Imagery Provided by Apple maps
Apple provides high resolution satellite images through its Maps application for significant portions of Northern Canada. In many areas exceeds its resolution the base layers provided through Google Earth,
In this study area the image below in Figure 5 shows the Thaw slide area in and around 2014-15. The resolution is in this case comparable to the GE image used dated 2004-06-16.
FIG 5 Apple Maps image
FIG. 6: Apple Maps Image overlayed on Google Earth 2004 Layer. The following LINK to a KMZ fileallows a more detailed study of the difference between the two images and analysis of changes. With the KMZ file on Google Earth, the transparency of the Apple overlay can be changed.
FIG. 7 2004 Google Earth Layer: The 2014 melting edge is mapped as green line. The linear melting distance varies from 150 to 250 meters over a period of 10 years