Google Earth (GE) provides a fascinating way to explore the earth remote ecosystems. Few people would imagine that Google Earth has the resolution and detail to monitor ecosystems, but an experienced interpreter can do remarkable things with Google Earth beyond the simple location of houses, urban areas and major landscape features. A 2005 Google Earth visit to one of my old research sites in Manitoba, Canada, showed that GE can be used to approximate the melting rates of permafrost in peat landforms.
In 1974, I published an article on the "Distribution and Melting of Permafrost in the Southern Part of the Discontinuous Permafrost Zone in Manitoba. (Arctic, Journal of the Arctic Institute of North America, Volume 27, number 3, September 1974). With Google Earth I revisited the area in 2005 to reassess the melting rates which I had measured in a previous study in the early 1970's. Using my field work between 1969 and 1972 as reference, and satellite images provided through Google Earth, Apple and Bing Maps, a good estimate of the melting rates in the last 35 years ab be obtained.
In addition to the field work, carried our as part of the Canada Land Inventory Program between 1969 and 1972, the changes of permafrost (in the form of palsas and permafrost peat plateaus) were measured with aerial photography taken over a period of 20 years. At that time it was estimated that 25% of the once occurring permafrost (maximum extent) was still present. Also melting appeared to have exceeded the aggradation of permafrost since about 180 years before the present. Two types of collapses were dominant: peripheral collapse around very small permafrost bodies; and a central collapse for the larger peat plateaus. The amount of collapse varied from 0-30 meters horizontally over the period of 20 years.
The image below shows the same area from a vertical perspective, using a winter image used by Apple Maps for this area. The probable date for this images is after 2011. The area shown corresponds with the area captured by the pointers on the images above. The winter images shows rings/ bands of slightly denser tree cover between the melted areas and the non-frozen fen wetlands. There are some small dark patches of higher trees (Black Spruce) left showing the small remnants of permafrost (P).
Using the interpreted aerial photographs from 1947, 1967 and Google images from 2005, it became clear that melting had continued between 1967 and 2005 at similar rates as in the period between 1947 and 1967. No clear acceleration of melting could be observed. The comparison of the 1947 aerial photo above with the Google Earth image shows a typical melting example.
More recent satellite images provided through Google Earth and Apple maps provide significant higher resolution images and confirm the continued melting. The figure below shows on the left the Google Earth image, already a significant improvement over the 2004/5 image. The Apple Maps images shows likely a spring situation with e relative high water table. Surface water is clearly visible in the more recent collapsed areas. The still existing permafrost is marked with a P. It is also clear from these images that the wildland fire which burned the lower peat plateau did not affect the melting rate of the permafrost when compared with the non-burned top plateau. In fact the reverse could may be possible.
As a point of interest, the two images below could be looked at in stereo vision with or without a stereoscope. The pseudo 3D effect can enhance some of the differences between the two situations.
It is interesting to note that Parks Canada is developing a National Park in this area, which has probably one of the most interesting and accessible examples of discontinuous permafrost in Canada.
Below is a series of aerial photographs which show the relationship of melting to the size of the permafrost landforms. This is Figure 4, from page 195 from the paper "Distribution and Thawing of Permafrost in the Southern Part of the Discontinuous Permafrost Zone in Manitoba", published in ARCTIC, Journal of the Arctic Institute of North America, Volume 27, number 3, September 1974
As comparison with the figure 4 above, I have selected the same locations on high resolution Apple maps images- dated around 2013-14. Google Earth does not provide adequate resolution to make accurate comparisons.
Some quick differences:
The small permafrost areas in Fig 4A have all but disappeared now; In Fig 4B the permafrost in the small peat plateau (2) is now gone, all you see is surface water and a ring of stunted trees, mainly Tamarack, growing on non-frozen wetlands; In Fig 4C some small patches of permafrost are left; the most recent melting is represented by the yellowish colours;
in Fig 4D above some permafrost is left in the edge of the peat plateau; in the comparable image below virtually all permafrost is gone now;
The Following ground and aerial (helicopter) pictures were taken in 1970 during fieldwork for the Canada Land Inventory Project (CLI), to complete a biophysical and land capability classification for forestry, by Jean Thie, at that time Chief of the Forestry Sector, CLI Manitoba.
|An active collapse edge in a peat plateau just a few hundred meters north of Limestone bay. Black spruce -feathermoss is the typical vegetation on the permanently frozen peat (3), the green sphagnum moss dominates (2)in the active collapse area. A permafrost tongue was still present at 70 cm below the surface. Hummock building sphagnum mosses are coming in near (1).
Small collapse area. Same as in the previous picture. It is actually the light bright spot in the centre of grey aerial photograph. Dave Klippenstein and Don Forrester are crossing this area walking on the sunken tree trunks, otherwise they would go down more than waist deep.
The two ground photos above were taken near the point of the red arrow on the 1967 aerial photo. The 2011 satellite image shows that virtually all permafrost has melted. Surface water is visible in the more recently melted areas. This is partially the result of snow melt on this early spring satellite image.
|Circular collapse of palsa surrounded by Tamarack fens. The black spruce in the middle grow on the frozen core. They are about 12-15 meters in height. They collapsing edge shows surface water and leaning trees and trunks sinking in the non frozen wetland. The Tamarack growth is denser around the original edge of the palsa
|Extensive collapse scars of former peat plateaus. Very little permafrost is left except for areas near (2). This area was burned a number of years ago and ion the small areas of permafrost white birch and black spruce regeneration is seen. The relative recent collapse areas are marked with (1), older scar areas with (3)
|A completely collapsed palsa in a ribbed Tamarack fen. The original extent of the permafrost is still visible in the teardrop shape image. Ground water drainage flows are indicated by arrows.
Impact of Forest Fires On Permafrost in Peat plateaus
This is an example of a 1930 fire which burned part of a large peat plateau complex. After the burn black spruce regenerated naturally and no increased melting was observed in 1974. Even in 2004 this Google Earth image shows that permafrost still exists with a similar distribution as in the non burned area. Melting has continued at a steady pace e.. Fire records in this area do not show significant fires in the last 15 years. A few very small areas can be found ( see recent small burn), bit the immediate impact of those cannot be assessed. GE resolution is not adequate for that in this area. Although fire generally did not have an impact of acceleration of melting rates, one particular small peat plateau totally collapsed after a burn.
|This picture from helicopter was taken 1970. It shows the area burned in the previous image. The area B was not burned in 1930, the area A is also a part of a stand which survived the fire. The regeneration is primarily Black Spruce, with an occasional bright dots of White Birch. The light coloured collapse areas around the edge and in the centre are quite distinct.
|Typical fire regeneration on permafrost peat plateaus in this area, trees are 30-40 years old. The peat auger in this picture is in the permafrost which is at about 50 cm (late August).
The composite figure below shows a combination of a 1926 oblique aerial photo, a 1947 vertical air photo projected as oblique and a 2005 oblique Google Earth image. The permafrost around A is still present in 1947 but totally melted in 2004. The peat plateau B shows some melting (collapse holes) inside the plateau in 1947; but in 2005 they joined together and are forming a peripheral collapse. Area C is interesting because it was burned before 1926 regenerated a black spruce cover and shows still its frozen state in 2005. In fact the melting process in B and C seems very comparable. So fire does not necessarily increase the rate of permafrost melting. On the other hand, the the small peat plateau at touching the top of (A) melted within years after a fire in the late 60's.
jean.thie at ecoinformatics.com