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Diamond Cave [Fair Isle] (N entrance)

Colsta, Fair Isle, Shetland.

A mostly subtidal seacave surveyed by a Heriot Watt team in 2021 as part of Nature Scotland Report 1145. This entrance is intertidal.

The southern cave entrance was ~14 m in width at the waterline with a ceiling at ~9 m ACD. The cave consisted of a single linear passage trending NE and extending for ~200 m from the southern entrance and connecting into Troila Geo at a northern entrance. Passage dimensions remained considerable throughout the cave but became narrower towards the north. Width was reduced to ~6.5 m at 85 m from the southern entrance and narrowed further towards the northern entrance. Passage shape was in the form of a rift inclined to the NW. Cave floor at the southern entrance was at ~7.5 m BCD and progressively shallowed within the cave. Floor depth at 85 m from the southern entrance was ~5 m BCD and the floor of the northern entrance was an intertidal (~0.7 m ACD) cobble beach. The cave floor was predominantly composed of boulders with cobbles, pebbles, and sand infill. Some extensive areas of rippled sand were present deeper within the cave. For example, the majority of the cave floor was composed of rippled sand from about 75 to 90 m from the southern entrance. Time constraints prevented the completion of a full physical survey but snorkellers swam through to inspect the northern entrance.

Alternative Names: None recorded.

Notes: Length is calculated from the NGRs of this and the north entrance. The above NGR was obtained by a consideration of the camera location of photo 1 and Bing Aerial. There appears to be an error on most OS map layers in that they show Triola Geo too far north - as can be seen in the map on this page.

Other dimensions from report 1145.