Monitoring Melting of Permafrost with Google Earth
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, Google Earth has enough resolution to get a rough idea about the melting rates in the last 35 years.
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 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.
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.
Satellite image resolution has increased as is visible in the two images below. The 2006 Google Earth image and the on the left and the Apple Maps image on the right below demonstrate that melting can be clearly seen and measured using high resolution satellites. A higher resolution Google Earth image is available [here]. The areas marked with P have permafrost on both images. The white arrow shows surface water, which surrounds much of the remnants of the frozen peat plateaus. Dead trees disappearing in the wetlands can still be seen in some of these areas.
The 1967 air photo below shows the melted areas between 1947 and 1967. The 1967 permafrost is delineated with the black line. The areas melted in this period of 20 years are highlighted in red (based on fieldwork, helicopter flights and air photo interpretation in 1971. The outside edge of the large peat plateau did not change much between 1946 and 1967, since that time it regressed by 40 to 65 meters in many areas, with most of this in the last twenty years.
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
Typical example of crossection of a palsa in this Ecodistrict.
|This cross section of a Palsa close to Cranberry Portage was made by Steve Zoltai and Charles Tarnocai who worked on the description of Palsa and peatplateaus in this area between 1968 and 1970. It is very representative of Google Earth example.The glacial lake Agassiz clays are covered by up to 2 meter thick organic layers, in which permafrost developed as part of an complex interaction of climate, vegetation and micro-climate|
|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 Klippendstein and Don Forrester are crossing this area walking on the sunken tree trunks, otherwise they would go down more than waist deep.
|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 Peatplateaus
This is an example of a 1930 fire which burned part of a large peatplateau 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 pac 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 peatplateau 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 colored collapse areas around the edge and in the centre are quite distinct.|
|Typical fire regeneration on permafrost peatplateaus 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).|
For more information contact jean.thie at ecoinformatics.com