Periglacial landforms and landscapes in the Falkland Islands

Abstract

The Falkland Islands experience a cool oceanic climate with a moderate rainfall. They are formed largely of sedimentary rocks which display a range of structures. Across the widest part of East Falkland; in a zone of folding of varied style, prominent quartzite beds form or strengthen high ground (600-700 m). This tract of hills and the surrounding lower ground is diversified by a series of erosion surfaces.

In its major elements this landscape shows the consequences of declining levels of planation but the products of cold climate geomorphic processes are widespread. In the past the long-known stoneruns have generally been regarded, whatever the details of formation postulated, as cold climate features. However, their place in a suite of landforms and their significance as a component in an erosion-transport-deposition system has not been previously established.

It is now possible to discuss this suite and the erosion system more completely, and to establish relationships between the various parts. Hill tops are characterised by blockfields; altiplanation surfaces and residual tors; hillsides by frost-riven crags, scree, block-terraces, and stoneruns. Valleys are largely ericumbered by stoneruns and head, the latter also forming extensive sheets on the lower ground. Evidence of the consequences of severely cold climate is extended by the description of a number of corries (cirques) in the highest and most extensive uplands, of thaw lakes and depressions, and of patterned ground.

Amelioration of climate led to the formation of smaller debris terraces after the larger block-terraces ceased to develop. There is evidence that since the periods of most severe cold rivers continued to discharge much greater volumes and loads than they now do. That the phases of severe and declining cold were not a simple progressive sequence is shown in the interbedding of organic and minerai deposits noted from coastal exposures. Terrestrial deposits extend below present sea-level and drowned valleys are traceable to depths well within those possible during the last major glacio-eustatic withdrawal of sea. Coastal materials show that the climate was still subject to significant fluctuations at the time of recovery to present level. The present climate appears to be one of much reduced morphological activity with little frost action; rivers are generally sluggish and underfit.

Both worldwide and especially regional circumstances concerned in producing the local cold conditions are considered. The degree of cooling adequate to produce an environment rigorous enough to form the landorms was very similar to that for British and continental European periglacial phenomena.