ABSTRACT: Rock slope adjustments in west Newfoundland: Rock glaciers and slope failures.

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Abstract

In west Newfoundland (WNL) highlands, 10 rock glaciers (RGs) and ~12 rock-slope failures (RSFs) mark glacially steepened plateau margins, most in highly fractured, oceanic, mafic and ultramafic rocks of the Early Paleozoic Humber Arm Allochthon. The rock glaciers (Brookes, CANQUA 2007 Abstracts, p.44) are mostly simple, of the talus-foot type, and post-date Late Wisconsinan (LW) glaciation (one possibly by some millenia; no numerical ages have been obtained). The rock-slope failures (RSFs) vary greatly in size and age. The largest, on Lookout Hills in Gros Morne National Park (GMNP), is mainly a post-LW feature. It has a multi-arcuate head-scarp, 7 km long, 40m high, a 600 m summit, with multiple failure scarps and crack networks below. It also bears evidence of pre-LW failure in mild glacial streamlining of failed masses. The second largest RSF, in the SW Lewis Hills, has a straight head-scarp, 4 km long, but (remarkably) only 5-10m high and, from the absence of dissection on it, appears to be recent. It is oriented N-S, close to the coast, and indicates long-delayed (why?) failure in response to steepening and/or debuttressing of this highland edge by LW Newfoundland ice deflected SW by highland relief and changing orientation of its margin. Beside Trout River Ponds in GMNP a rock-mass has slipped ~ 500m from the S edge of ‘Tablelan ds’ to near sea-level. It was previously mapped as down- faulted, but it crosses fluting in till and has ice-grooved rock on its summit, so is assigned a pre-LW age. Other examples of RSFs are simpler, although pre-LW and post-LW ages are still indicated. Several of these RGs and RSFs are illustrated in (i) Brookes (1993), Can. Geogr. 37, 69-75, (ii) GSC Misc. Rpt. 54 (1992), comprising GSC Map 1769A, and (iii) Osborn et al. (2007) CJES 44, 819-834.

Bibliography of Canadian Geomorphology