blockfields

tors

 

 

Maiden Pap

 

Image by   Alan Moar

Periglacial Landscapes

Defintion: any area with a tundra climate, such as mountainous areas in mid-latitudes, or where frost processes are active or permafrost occurs in some form.

Processes operating under a cold climate have a limited effect on the landscape of Caithness today.  Most periglacial features however date from the cold periods at the end of the Ice Age.

We can identify several generations of periglacial features in relation to known cold periods.

  • Active periglacial features developed in the Holocene.

  • Fossil forms and sediments developed during the Loch Lomond Stadial, a short period of intense cold 12,000-10,500 years ago

  • Fossil forms and sediments which date from the period when ice was retreating from Caithness around 16,000 years ago

  • Landforms which predate the last ice sheet, most notably the tors of the Langwell Forest.

Active features

The hills of Caithness show a number of periglacial features, a reflection of their exposure to high winds and rainfall and to winter frosts and snow. A range of periglacial processes appear to be active, including solifluction, frost shattering and wash. Ploughing boulders occur on hill slopes and scree is actively accumulating, particularly beneath quartzite cliffs. On the low ground however, there appear to be few active periglacial features.

Loch Lomond Stadial

It is often difficult to attribute particular features or sediments to specific cold phases. At Wag and Ellanmore  peat occurs which developed during the warm stage immediately before the Loch Lomond Stadial. This is overlain by soliflucted glacial deposits and demonstrates widespread mass movement on the low ground of Caithness during the following cold period. Permafrost may have extended down to sea level at this time.

Deglaciation

As the ice withdrew from Caithness, it is likely that the climate remained cold. The tops were ice-free by 18,000 years ago and the low ground by 15,000 years ago. The newly exposed ground was largely bare of vegetation and the unconsolidated covers of newly deposited glacial deposits would have been prone to slumping and wash. It is likely that the upper part of many exposures of till has been disturbed by this kind of mass movement but no detailed studies have been carried out. Smith (1977) notes that considerable thicknesses of frost-shattered rocks and solifluction debris may exist at the base of slopes and extend close to sea level in Berriedale - this mass movement may represent the combination of activity during deglaciation and the Loch Lomond Stadial. Omand (1972) recognises accumulations of angular frost-shattered material at Ben-a-Chielt, Sarclet Haven, Ousdale and south of Loch of Yarows.

The period before the last ice sheet

On the hilltops in southern Caithness are found features from earlier cold stages. The tors have evolved by differential weathering and erosion, probably including long periods of cold climate when the ice was not sufficiently thick to cover the hilltops. Under these conditions it is possible that frost action has been important in tor formation, although many tors do not carry of fringing apron of debris, perhaps due to removal by the last ice sheet. The blockfields so well displayed on Scaraben may include areas of deeper regolith which were preserved beneath cold-based ice during the last glaciation.