Geology Reference
In-Depth Information
sedge and tussock grass gradually disappear. An elevated peaty polygon fi nally emerges
surrounded by troughs along the underlying ice wedges.
8.5.3. Badland Thermokarst Relief
Dramatic badland-type relief can occasionally develop as the result of thermal melting
and erosion operating preferentially along large ice-wedge systems in unconsolidated sedi-
ments. For example, in an area drained by two streams on Eastern Banks Island a large
amphitheatre-like hollow, over 0.5 km in diameter and several hectares in area (Figure
8.9), is being eroded within a thick sequence of glacigenic (lacustrine) silt that possesses
20-30% excess ice on average and contains ice wedges exceeding 6 m in depth (French,
1974b, pp. 791-793). Fluvial erosion, currently operating preferentially along the ice
wedges, has led to the isolation of sharp conical mounds within the depression and a ser-
rated edge to the amphitheatre. Mudfl ows and re-sedimentation go on within the depres-
sion and the mounds are degrading due to their exposure to thaw from all sides. This
terrain appears similar to some of the thawing permafrost features fi rst described by
Ermolaev (1932b, pp. 7-10) from Lyakhovski Island in the Laptev Sea of northern
Siberia.
Figure
8.9.
Oblique air view of badland thermokarst formed in ice-rich silty sand, eastern Banks
Island. Thermal erosion is preferentially concentrated along ice wedges producing residual mounds
over 8 m high. Remnants of the original polygon surface can be seen in the foreground and
mid-distance.
8.6. THAW LAKES AND DEPRESSIONS
Thaw lakes are exceedingly common in arctic tundra lowlands. For example, in the
Tuktoyaktuk Coastlands of the Western Canadian Arctic, over 10 000 lakes exist (Mackay,
1963), and many thousands more occur on Banks, Victoria, and the other Arctic islands.
Likewise, thaw lakes are numerous on the Alaskan coastal plain (Hinkel et al., 2005;
Sellman, et al., 1975), interior Yukon (Burn and Smith, 1988b), and on the alluvial low-
lands of northern Eurasia and Siberia (Dostovalov and Kudryavtsev, 1967; Romanovskii
et al., 2000; Tomirdiaro and Ryabchun, 1978). In fact, they are ubiquitous in fl at-lying
