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
2: Caribou River, 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of Canada, unpublished data).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).
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Figure
1 The Permafrost slide area as seen on Google Earth 2007 : original
source 2007 Digital Globe high resolution image. The red marker
is from the selection of regressive permafrost slides marker
selection provided by Kingpointnorth. The relative recent disturbed
bare soil is clearly visible on both sides of the creek. Also
the adjacent areas on both sides show significant sliding area
which
appear to have been stabilized and are recovered with vegetation. 
The complexity of the slide area and the apparent long history should make it
an interesting object for further study. The images and discussion
below give a simplified historic perspective based on the interpretation
of satellite and airborne images taken since 1950.
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Figure
2 Interpretation of the History of the Permafrost Slide Area.
This figure represents the air photo and satellite image interpretation since
1950. The earliest available air photos taken in 1950 showed
that the first slide started on the right side of the creek,
in effect
the south facing slope. It appears to have been a sudden event.
The pink arrow shows the slide path, which also blocked the creek
flow, and created a small lake upstream. The the water erosion
from the displaced creek started to undermine the north facing
slope which showed a steady regression for the next 27 years
before stabilizing. Just before the 1990's additional regression
occurred on the south facing slope (thin orange line) also occurring
as a sudden failure. The new slide areas (yellow dotted line)
developed between 1990 and 2000.
Wildland fires are not the cause of the melting in this case. During the period
1950-2007 no wildland fires were recorded (see below) nor any
signs of
fire
marks were
visible
on any images
since
1950. The closest fire was about 5 km distance from this
location.
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Figure
3. Retrogressive Slide on 1950 and 1953 Aerial Photos
The 1950 photo ( A12847-144) was taken on August 2nd, 1950 at a height of 20'000
ft. Original scale 1:40'000. The pink arrow shows the flow direction.
The slide, on the south facing slope occurred as a sudden event
blocking the flow of the creek and creating a small lake upstream.
The drainage channel was pushed into the opposite slope which started
to collapse. Both sides continued to melt, but most of the
regression in the following decade is in the north facing slope.
The 1953 airphoto (A13753-22) was taken on 27 July from 35'000
ft. |
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Figure 4. The Next 20
Years
During the next 20 years the North facing slide is regressing. The 1972 and 1977
air photos show that the creek is pushed back again (yellow marker).
In this 5 year period the North slide appears stable, and some
further sliding occurred on the south facing slide (from blue
dotted line to the light blue-grey dotted line). There are no
signs of fire scars in the vegetation on these photos, but a
fire scars ( (dated between 1958-1978) were identified in close
to
the Salter Hill area, about 5 km distance from this slide area.
1972 Airphoto (A22972-119) taken on 11 July, from 35'000 ft;
1977
air photo (A24761-133) taken on August 1, from 35'000 ft.
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Figure
5: NASA Landsat Pseudo Colour 1990 (left) and 2000 (right). The pink arrow on the 1990 satellite image shows that the south facing slope
has become active again. Also the light blue arrow shows the
start of the next phase on the north slope. The 1950 and 1970
slide areas still look reasonably stable and are covered with
vegetation again. The red arrow on the 2000 image shows a part
of the 1950 slide which has become active again: the small dark
black area- a mudflow The
yellow arrow on the 2000 image points to the dark purple active slide area essentially very similar to the Google Earth image (2007).
No fire scars are visible on each of the images.
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Figure
6: Fire
History for the Yukon 1946-2004. The map below depicts the wildland fires since 1946. Source: Yukon Energy, Mines
and Resources. The Caribou River area described here is marked
with the red marker near (1). The closest fires on this map was
(3) which occurred between 1990 and 1999. The Trevor Range Site (green marker) is identified with a (2). It will be interesting
to study the blue markers provided by kningpointnorth in relation
to fire history. A cursory review of some of the sites in recent
and older burn areas seems to imply a link with the fires. Legend:
Grey= 2000-2004; Red=1990-1999: Pink=1980-1989; Green= 1970-1979;
Orange= 1960-1969; Yellow=1950-1959; Light Green= 1946-1949 (not
on this part of the map)
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Figure
7: Topographic Map of Study Site (red circle) |
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