Chapter 5: Vegetation

5.31: Non-Oriented and Oriented Lakes South of Churchill

This area is within the northern part of the discontinuous permafrost zone near Cromarty on the Hudson Bay Railway line just off the photo to the west.

In this area peat that is typically about 2 metres thick overlies glaciomarine silt or silty till. The peat began to develop about 6500 years ago as the post-glacial Tyrrell Sea withdrew from the Hudson Bay Lowland. With the onset of a colder climate, permafrost invaded the peat. “The development of tundra ponds begins with the thawing of ice wedges, followed by seepage of water into the central part of the peat polygons, causing thawing and then subsidence. Continual wetting and refreezing of the peat increases its thermal conductivity and rate of thawing until shallow, flat-bottomed ponds are created. These ponds enlarge, coalesce and deepen by the melting of ground ice and subsidence until the glaciomarine silt or silty till is reached, which forms the flat floors. With continuation of this process the coalescing ponds expand in time to form small lakes. These lakes may enlarge even more from lake ice push, wave action and undercutting of the peat in summer, and from thermal erosion by warmed water around the peaty lake shores.”[i] Numerous roughly circular ponds 1 can be seen. These lakes are flat-bottomed and generally less than 3 metres deep. Also seen are many larger lakes, the largest of which are Lovell Lake 2 and Morantz Lake 3. These lakes are flat-bottomed, probably less than 3 metres deep. Several drained lakes—light-toned—can be seen 4. The prevailing northwest winds push water, waves, currents, and sediments to the southeast forming prograding shelves in several locations 5. Also resulting from these processes are straight southeast shorelines on several lakes 6. Dark tones along Kelsey Creek 7 indicate melting of permafrost along the riverbanks.

In the northeast is an elevated area—about 200 feet (61 m) a.s.l.—with spit-like ridges 8 which probably represents an old Tyrrell Sea shoreline. A spur from the Hudson Bay Railway line 9 runs to this area in a series of straight stretches avoiding lakes. Very light-tone areas 10 at the eastern end of the spur are probably sand and gravel pits exploiting the raw materials in the spit.

Figure 5.31: Non-Oriented and Oriented Lakes South of Churchill

Figure 5.31

Vertical air photograph: A14126-118

Flight height: 31,000 feet a.s.l.; lens focal length: 6.03 inches

Scale: 1:61,800 (approx.)

Date: July 1, 1954

Location of Lovett Lake: 58° 07'N, 94° 02' W

Map sheets: 1:250,000 54L Churchill

1:50,000 54L/I Cromarty

Notes

[i] Mollard and Janes op.cit., 1984,127.