The Pinnacle (sea stack)
Sea stack in Dorset, England
From Wikipedia, the free encyclopedia
The Pinnacle is a sea stack located off Ballard Down on the Isle of Purbeck in Dorset, southern England. It is the tallest of two stacks in The Pinnacles, the other stack being Little Pinnacle, and rises to a height of 33 meters.[1][2][3][4]
The Pinnacle from Ballard Down | |
 Interactive map of The Pinnacle | |
| Geography | |
|---|---|
| Location | English Channel |
| OS grid reference | SZ052819 |
| Type | Sea stack |
| Archipelago | The Pinnacles (Dorset) |
| Adjacent to | Little Pinnacle |
| Total islands | 2 |
| Highest elevation | 33 m (108 ft) |
History
Formation
About 65-100 million years ago, this region was home to a warm, shallow tropical sea. Chalk developed as a result of the build-up of the small, calcium-rich skeletons of microscopic algae found in the sea, called coccoliths.[5][6]
These eventually built up into thick bands as a result of compaction over millions of years. Thick bands of flint, comprising siliceous spicules of sponges, were present within these bands and offered some degree of structural strength to resist erosion. Eventually, due to tectonic activity, these layers of chalk rose above sea level. At this point a ridge of chalk existed to connect the Isle of Purbeck with the Isle of Wight, specifically the Needles. After the last Ice Age, due to rising sea levels and the breaching of this land bridge 7,000 to 10,000 years ago, these two landmasses were separated.[7][8]
To form The Pinnacle, the sea gradually eroded along the joints and bedding planes where the softer chalk meets harder bedrock of the rock formations to create a cave. This eventually eroded right through to create an arch. The arch subsequently collapsed to form The Pinnacle.
Folklore
The Pinnacle has traditionally been a notable coastal feature for mariners to use when navigating the approaches to Poole Harbour from the east. Its shape has been a notable visual aid in a complex coastal landscape. The stack, along with Old Harry Rocks, has also been associated with the 14th-century pirate Harry Paye. Local folklore has it that the pirate hid his ship in the vicinity of the stacks and used the position to attack merchant vessels.[9][10]
World War II
During World War II, The Pinnacle, along with other stacks in the area- including the nearby Old Harry- were used by Spitfire and Hurricane pilots for target practice.[11] Divers still occasionally find shell cases on the seabed nearby.[12]
Etymology
The name "The Pinnacle" is derived from the tall, narrow, columnar shape of the structure. The smaller stack nearby, also part of The Pinnacles, is named Little Pinnacle but is also referred to as "The Haystack" or "Turf Rickrock", which refer possibly to its more rectangular and agricultural appearance.[3]
The clifftop location above the stacks is named "Old Nick's Ground", which is derived from the traditional English term "Old Nick", meaning the Devil.[13]
Ecology
The stack serves as a critical nesting site for several species. The Pinnacle South Cliff is an important breeding spot for cormorants, with up to 16 active cormorant nests.[14]
Around 1900 the stack was a documented nesting site for peregrine falcons, which used concealed holes at the summit to rear their young.[15] Williams Masters Hardy visited The Pinnacle in 1910 and wrote:
Agglestone Rock has been the habitation of a pair of penegrine falcons for ages back. They rest and hunt there, but build their nest and rear their young on the top of Pinnacle Rock, near Old Harry. Their nest is artfully concealed in a hole in the summit, which has an opening at both ends, through one of which they enter, emerge at the other, the nest being most skilfully concealed from all nest seekersor destroyers of their own or any other species. The reason why these birds can be so seldom seen is because of their wonderful keen sight, for as soon as the "man with the gun" is observed at the most distant range, the birds swoop down from their aerial abode and wind their flight to their retreat to the Agglestone or some other isolated spot, long before the eye of the fowler has detected them.[15][16]
Peregrine falcons continue to use these stacks as a nesting site as well as others in the area such as Durdle Door.[17] They traditionally breed on the apex of the stack, which is in the shape of a triangle.[15] Today, they can be found perched on top of the stack, hunting for pigeons and other small seabirds.[18][19] The Pinnacle is also home to various species of Fulmars, Kittiwakes, Guillemots and Razorbills.[20][14]
The base of the stack is home to a rich marine ecosystem, which is protected as part of the Studland to Portland Special Area of Conservation (SAC). The intertidal zone on the lower chalk areas is highly colonized by barnacles and limpets as a result of being exposed at low tide.[21] Barnacles and limpets can also be found at the base of the stack on the wave-cut platform and in rock pools. Seaweed and various crab species are also found in the surrounding tidal areas. The surrounding waters within the subtidal areas are home to rocky reefs and seagrass beds within Studland Bay, which are used as nursery grounds for commercial fish species and seahorses.[22][23]
Geology
The downlands of Ballard Down are formed of chalk with some bands of flint, and were formed approximately 66 million years ago. The bands of stone have been gradually eroded over the centuries, some of the earlier stacks having fallen while new ones have been formed by the breaching of narrow isthmuses.[24] Across the water to the east the Needles on the Isle of Wight are usually visible. These are also part of the same chalk band and only a few thousand years ago were connected to Ballard Down.
Geography
The Pinnacle lies directly east of Studland, approximately 200 metres south of Old Harry Rocks and about 4 kilometres northeast of Swanage.[25] The chalk headlands of the Ballard Downs are owned by the National Trust. The rocks can be viewed from the Dorset section of the South West Coastal Path.