ploughing blocks

protalus ramparts

rock glaciers

avalanches

 

 

A contemporary solifluction slope in Siberia, showing lobes and terraces and the gradual displacement of material downslope towards the river.

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Joint-controlled steps and soliflucted boulders on Lurcher's Crag

 

 

 

 

 

 

 

 

 

 

Solifluction sheets on the slopes of Cairn Lochan

 

 

 

 

 

 

 

 

Bedded, platy clasts of frost-shattered psammite forming a thick layer of solifluction deposits in a valley head in the Ladder Hills

Solifluction

Definition: Mass movement of soil and regolith affected by alternate freezing and thawing. Characteristic of saturated soils in high latitudes, both within and beyond the permafrost zone.

A number of features of the Cairngorm environment contribute to active solifluction:

  • frequent freeze-thaw cycles
  • saturated soils and regolith, after snow melt and heavy rainfall
  • frost-susceptible materials, with significant contents of silt and clay, at least at depth
  • extensive regolith across a range of slope angles

Solifluction adds detail to the terrain underfoot. Small-scale, active landforms include lobes and sheets (Sugden, 1971) and turf-banked terraces. The latter reflect also the action of wind in stripping and shaping the vegetation mat and frequently occur in association with deflation surface (Gordon, 1993). Ongoing mass movement is also indicated by 'ploughing boulders' - large blocks that are moving downslope, pushing a rampart ahead of them and leaving a furrow behind.

Much more striking, however, are the large boulder terraces and lobes that give crenulated patterns to many granite slopes on the plateau. These steps terminate in stone banks up to 3 m high. These forms are absent from within the limits of Loch Lomond Readvance glaciers (Sisson, 1979) and so date from this or earlier periods. As delicate features such as tors have survived beneath ice covers, it is possible that the larger solifluction terraces and lobes may be of considerable age.

Although solifluction deposits are not an obvious feature on the Cairngorm Granite, considerable thicknesses of frost-shattered and soliflucted debris occur on Dalradian metamorphic rocks in the Ladder Hills.