rock glaciers avalanches solifluction

A puzzling ridge

Students on the highest part of the ridge.

Notice the quartz vein debris

A simple model of the formation of a protalus rampart

 

 

 

 

 

 

 

The southern part of the ridge, where a pre-existing moraine has been over-ridden by a Loch Lomond Stadial glacier. The moraine lacks the loose debris of large boulders which makes movement through the rest of the corrie floor so difficult.

Protalus Rampart

Definition: Unsorted, non-stratified, coarse angular rock debris forming arcuate low ridges. Associated with former persistent snow banks in shaded sites, commonly at base of corrie headwalls.

'Protalus rampart' is an overblown title for a simple landform. It requires the existence of long-lived snow banks below rock cliffs. Frost weathering leads to rockfall from the cliff and the blocks roll down the snow slope to accumulate at its base. Ballantyne and Kirkbride (1986) describe good examples from below the Devil's Point and Srn na Lairige.

Sissons (1979) described a large "protalus rampart" on the N side of the floor of Coire an t-Sneacdha. The ridge certainly has a suitable form and location but its origin has been disputed, with others regarding the ridge as essentially formed in rock (Ballantyne in Gordon, 1993) or as a moraine at the upslope limit of the advance of Strathspey ice (Brazier et al., 1996). The ridge is one of many reasons for field groups to visit this corrie. Questions for discussion include:

  • is the northern part of the ridge essentially a bedrock form?
  • is the valley on its eastern side a meltwater channel or simply a structurally-controlled dell?
  • can any metamorphic erratics be found on the ridge to support movement of ice from outside the corrie?
  • is the southern extension of the ridge a moraine related to a small glacier below the Mess of Pottage buttress?
  • the southern part of the ridge was clearly over-ridden by ice from the inner corrie during the Loch Lomond Stadial. When did this moraine form?