Pentland Firth
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The Pentland Firth, which is actually more of a strait than a firth, separates the Orkney Islands from Caithness in the north of Scotland. The name is presumed to be a corruption of "Pettland's Firth", the fjord of Pictland, and is completely unrelated to the Pentland Hills near Edinburgh.
[edit] Geography
On the Caithness (southern) side the Firth extends from Dunnet Head[1] in the west to Duncansby Head[2] in the east, while on the Orkney (northern) side from Tor Ness on Hoy in the west to Old Head on South Ronaldsay in the east.
In the middle of the Firth are two significant islands, Stroma[3] and Swona. The small Pentland Skerries group are in the east. The islands of Hoy and South Ronaldsay border the firth to the north and are part of the Orkney Islands.
The most northerly point of the headland of Dunnet Head, Easter Head, is also that of mainland Britain. The famous John o' Groats,[4] Mey (site of the Castle of Mey), and many smaller villages are also to be found on the Caithness side.
The town of Thurso and Scrabster Harbour are on the Caithness shore, in Thurso Bay, on the western fringe of the Firth. A ferry runs through this fringe from Scrabster to Stromness on the Orkney Mainland. Across the Firth itself a ferry runs from Gills Bay near John o' Groats to St Margaret's Hope on South Ronaldsay and, in the summer months, a passenger-only ferry runs from John o'Groats to Burwick on South Ronaldsay.
The Firth is well known for the strength of its tides, being among some of the fastest in the world, a speed of 16 knots (30 km/h) being reported close west of Pentland Skerries. The force of the tides gives rise to overfalls and tidal races which can occur at different stages of the tide. Some of the principal tidal races are:
- ‘The Merry Men of Mey’. Forms off St John’s point in the west-going stream and extends as the tide increases NNW across the firth to Tor Ness. The worst part is over a sand wave field about 3½ miles (5.6 km) west of Stroma. The waves formed by this race form a natural breakwater with relatively calm water to the east of it, particularly noticeable when a westerly swell is running. Tides in this area can exceed 10 kts (18.5 km/h).
- ‘The Swilkie’. The race at the north end of Stroma, off Swilkie Point is known as ‘The Swilkie’. It extends from the point in an easterly or westerly direction depending on the tide and can be particularly violent. The whirlpool of the same name was, according to a Viking legend, caused by a sea-witch turning the mill wheels which ground the salt to keep the seas salty. The name derives from an Old Norse term meaning "the Swallower".
- The ‘Duncansby Race’ forms off Ness of Duncansby at the start of the SE-going tidal stream (flood). Initially extending ENE but wheeling gradually anti-clockwise until it extends about 1 ml. (1.6 km) NW some 2½ hrs later at which point it is known as ‘The Boars of Duncansby’. During the time of the SE stream there is additional turbulence off Duncansby Head, particularly to the East. The race temporarily ceases at the turn of the tide before forming in an ENE direction in the NW-going tidal stream (Ebb) before ceasing again at the next turn of the tide. The race is particularly violent and dangerous when the tidal stream is opposed by gales in the opposite direction. During the east-going stream a race forms off Ness of Huna. This race can be particularly violent in an easterly or southeasterly gale.
- The ‘Liddel Eddy’ forms between South Ronaldsay and Muckle Skerry in the East-going stream (flood). A race also forms for part of the time off Old Head at the SE part of South Ronaldsay.
In addition to ‘The Swilkie’, races form at both the north and south ends of Stroma and Swona. Between the races there is a calm eddy which extends down tide as the tide strengthens. The races are highly visible with overfalls and whirlpools. Large swell waves can also be present, especially in bad weather conditions. When entering or leaving the eddies, crossing the races, even large powerful vessels can be pushed off course, such is the demarcation between the relatively calm eddy and the fast-moving tide in the races. There are other races in the firth particularly off Brough Head.
[edit] Notes and references
- ^ Latitude-longitude coordinates and Ordnance Survey grid references for Dunnet Head: , ND202767
- ^ Latitude-longitude coordinates and Ordnance Survey grid references for Duncansby Head point: , ND405733
- ^ Latitude-longitude coordinates and Ordnance Survey grid references for Stroma Lighthouse:
- ^ Latitude-longitude coordinates and Ordnance Survey grid references for John o'Groats: ND379735
