Falklands geology, at first glance, seems relatively simple. There is a little Pre-Cambrian gneiss and granite to be found in the extreme south west of West Falkland but a large portion of the rest of both islands is Silurian to Devonian and in the South of East Falkland, areas of Carboniferous to Permian, predominantly quartzite with some sandstones and mudstones. Basaltic and Dolerite dykes of Jurassic age occur over much of West Falkland. The land is never very high, the highest being Mount Usborne at 705 metres. Most of the views that we had, contained some rock even at a distance and most striking of all were the enigmatic stone runs.

The stone runs on Mt Kent

As I said, there is much quartzite. The beaches are a beautiful white sand and with abundant wildlife, some of that in danger of being blown up by mines left following the 1982 difficulties.
Stone Run formation
The quartzite bedrock has been subjected not only to weathering but to significant periods of freeze – thaw episodes during the last ice age which ended 15,000 years ago. Darwin in 1830 said of the stone runs: - “In many parts of the islands the bottoms of the valleys are covered in an extraordinary manner by myriads of great loose angular fragments of quartz rock, forming “streams of stones”… they are not thrown together into irregular piles, but are spread out into level sheets or great streams.” I would point out that the sides of the hills have stone runs that could hardly be described as occurring in valley bottoms.

York Bay, north of Stanley Airport

My own photograph of a stone run was taken for the wildlife (Black-Browed Albatross and Rockhopper Penguins) rather than for the stones but nevertheless shows the typical size of blocks and width of some of the runs. Yes, it shows a valley, but it is virtually dry and shows no wadi-like scouring action. In vertical profile stone runs show the largest boulders at the top, fining downwards and generally lie unconformably on unsorted stony soil. On higher ground at least, there is little colonisation by vegetation except for grey-white lichens which accentuate the whiteness of the stone runs but here virtually at sea level, the accumulation of guano may encourage eventual overgrowth!

West Point Island – NW of West Falkland

These stone run features are not unique and have been found in other parts of the world where there has been significant ice action, but here these periglacial blockfields and streams have taken on proportions peculiar to the Falklands. Some of the runs form immense interconnected sheets and some individual blocks are 6 metres in length. The largest single stone run in the Falklands is “Darwin Stone-river” known locally as “Prince’s Street”. It occurs south of Berkeley Sound to the north of Stanley and is 4 km long and approximately 500m wide, lining the floor of the valley floor like a glacier. This is in fact atypical of the Falklands as it is more river like than most and extends parallel to the strike of the underlying rock. Many stone runs are more related to the local topography, occurring as irregular or fan shaped sheets and coalescing into valleys or gullies which are often transverse to the trend of the folded or dipping quartzites.

Reading:
The Geology of the Falkland Islands. Mary E Greenway, British Antarctic Survey Publication No 76 1972
The Falkland Island Stone Runs. Stone and Aldiss, Falklands Island Government and BGS Publication 2001