Shetland rises from a basement platform that extends around 75 km to the W and 150 km to the E. On the Atlantic side the water depths drop rapidly at the edge of the continental slope into the Faeroe-Shetland channel. In the North Sea, the East Shetland Platform abuts against the Norwegian Trench, carved out by the great Scandinavian ice sheet.

The sea bed off Shetland. Note the continental shelf and slope, the Faeroe-Shetland channel and the Norwegian trench

Water depths around the inner coast of Shetland are highly variable, as would be expected from vast number of skerries and islets within the archipelago. Major deeps excavated by glacial erosion occur in Yell Sound and south of Scalloway.

Off the outer coast, water depths drop quickly to -50m. The deep water allows very large waves to arrive at the cliffs unbroken.Flinn (1964 and 1977) has identified submerged platforms around Shetland at a number of levels below present sea level (82 metres, 45 metres, 24 metres and possibly nine metres), Flinn suggests that these are remnants of former marine erosion surfaces