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Hilda Rock Glacier
A Rock Glacier was identified in Hilda Creek, on the boundary of the Jasper and Banff National Parks, in Alberta Canada, during fieldwork in August, 1995. It was a tongue-shaped, valley-floor rock glacier which extended downslope from a cirque(between altitudes of 2074m and 2346m) It was 1km long, covered an area of 1.5km² and had a NE-NEE aspect.

Thallus sizes of the lichen Rhizocarpon Geographicum were measured in two sample sites of 50m² . The ten largest thallus sizes are shown in the following table.
277mm243mm214mm180mm162mm
232mm215mm162mm162mm158mm
According to Luckman(1977) thallus sizes of 277mm, in this area equate to ages of up to 6600 years. This may be the case, however, it is generally accepted that lichenometric dating becomes imprecise beyond 3000years. Thus, the only conclusions that can be derived are that Hilda is between 2000 and 6600 years old(according to Luckmans growth curve), representing a mid-Holocene formation.

The terminus of the feature maintained a slope of 39°, and the marginal ridges maintained slopes of between 26° and 43°.


The rock glacier was advancing into the treeline despite colonisation of the lower section with vegetation. Evidence for movement included photographic comparison between a photograph of the terminus taken in 1985(Gardner and Bajewsky) and photograph taken during fieldwork in 1995.

Young trees which existed on the lower section of the feature expressed deformation in their trunks, inclined in the direction of movement. This is taken to represent the movement of the substrate on which they are growing.

A distinct micro-relief consisting of ridges and furrows was evident throughout the feature. It is generally accepted that these features are the result of flow and internal deformation, within the rock glacier.


The work of Gardner and Bajewsky indicates, with the use of discharge measurements that Hilda Rock Glacier may have an ice-core.

A large depression existed at the head of the rock glacier within the cirque. Although explanations for the existence of these depressions have been provided by permafrost origins, it seems that they are probably derived from the melting of a massive glacial ice-core.

The existence of a furrow which meandered from the head to near the terminus of Hilda was noted during fieldwork. It was concluded that this feature may have been the result of melting of an ice-core, to accomodate a sub-surface water channel, transporting water downslope. This water channel could then be described as being supraglacial but beneath the rock glacier surface.


The evidence presented seems to indicate that although some rock glaciers undoubtably form due to the deformation of interstitial ice, Hilda rock glacier formed during a mid-Holocene increase in glacier-rock glacier activity, when a cirque glacier became inundated with debris from the headwalls above. This veneer of rock protected the ice below from solar radiation, thus ablation was reduced and the cirque glacier was preserved under a thick layer of debris. The glacial ice-core continued to deform under its own weight and caused the continuing advancement of the feature downslope to form the rock glacier.


 

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