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of Canada, unpublished data).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.
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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 |
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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.
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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. |
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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. |
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