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- This page is on the geographical feature. For other meanings, see Mount's Bay (disambiguation).
Mount's Bay (Cornish: Baya an Garrek) is a large, sweeping bay on the English Channel coast of Cornwall, United Kingdom, stretching from the Lizard Point to Gwennap Head. In the north of the bay, near Marazion, is St Michael's Mount; the origin of name of the bay. Presenting a benign aspect to summer visitors of a large, scenic, natural harbour, in an onshore winter gale it presents a great danger to shipping as a "maritime trap", especially in the days of sailing ships with an excess of 150 known wrecks in the nineteenth century. The eastern side of the bay centred around Marazion and St Michael's Mount was designated as a Marine Conservation Zone in January 2016.
Geography and geology
Mount's Bay is the biggest bay in Cornwall. Its half-moon shape is similar to that of Donegal Bay in Ireland and Cardigan Bay in Wales, although, unlike the aforementioned bays, Mount's Bay is relatively sheltered from the prevailing Atlantic westerlies. It is, however, a danger to shipping during onshore southerly and south-easterly gales.
The coast is approximately 42 miles (67 km) miles from Lizard Point to Gwennap Head. Heading north and west from Lizard Point, the serpentine and hornblende schist cliffs reach a maximum height of 71 m (233 ft) at Vellan Head and are only broken by small streams and coves such as at Kynance, Gew-grade and Mullion Cove. After Gunwalloe Fishing Cove the cliffs have the softer look of Devonian Meneage Formations of greywacke and mélange, with erosion a problem either side of the naturally dammed ria of Loe Pool. West of Porthleven there are high Devonian slate and granite cliffs to Rinsey Head after which the cliffs are topped by Pleistocene periglacial head and have eroded to form sandy beaches such as those at Praa Sands and Kenneggy. These beaches are in deficit and the cliff line is retreating. With the exception of the harder Devonian dolerite and gabbro of Cudden Point, the low, eroding cliffs and beaches continue to Mousehole. This part of the bay is the most populated with the towns of Penzance and Marazion and the villages of Newlyn and Mousehole. Beyond Mousehole the granite cliffs, rise to 60 m, and are broken by small streams such as at Lamorna Cove and Penberth.
There are small sand dune systems at Church Cove and Poldhu Cove, Porthleven Sands, Praa Sands and from Marazion to Eastern Green, Penzance. The former sand dunes of the Western Green are now covered by Penzance promenade. All, but Marazion to Penzance, are examples of bay dune systems which develop where there is a limited supply of sand trapped within the shelter of two rocky headlands. Church and Poldhu Coves are SSSI and also have associated climbing dunes which occur when sand is blown inland of the main dune system.
Evidence of higher sea-levels in the past can be seen at Marazion where the town is built on a raised beach. A second example is the road between Newlyn and Mousehole. Sea levels rise and fall as the ice sheets advance and retreat, and raised beaches now mark the interglacial periods when sea levels were higher. Either side of Penzance, on the beaches at Ponsandane and Wherrytown, evidence of a 'submerged forest' can be seen at low tide in the form of several fossilised tree trunks.
Offshore surveys have found submerged erosional plains and valleys containing deposits of peat, sand and gravel. The deposits indicate cyclical changes from wetland, to coastal forest, to brackish conditions have been occurring over the past 12,000 years as sea levels rose. With the melting of ice-sheets and glaciers after the last ice age, sea levels reached their present levels about 6,000 years ago during what is known as the Flandrian Marine Trangression. Either side of Penzance, on the beaches at Ponsandane and Wherrytown, evidence of a ′submerged forest′ can be seen at low tide in the form of several partially fossilised tree trunks. Divers and trawlers also find submerged tree trunks across Mount’s Bay and the forest may have covered a coastal plain 2 to 5 kilometres further south than today. The samples of peat and wood around Penzance have been radiocarbon dated and indicate that the forest was growing from at least 6,000 to around 4,000 years ago when rising sea levels finally killed the trees. Artefacts dating from the Mesolithic (10,000 to 5,000 BCE) have been found indicating some occupation contemporary with the forest. Marshes formed and were overlain by sand, gravel and by sand dunes which formed natural barriers to the sea. Storms sometimes destroyed the barriers depositing sand and gravel over peat beds in Marazion Marsh, and in the foundations of many buildings in Wherrytown and Long Rock. The remains of these natural barriers can still be seen at Eastern Green and the dunes to the seaward of Marazion Marsh. The submerged forest in the intertidal area between Wherrytown and Long Rock is of national importance and is a Cornwall Geology Site.
At Loe Pool a barrier dammed the ria of the River Cober causing the formation of Cornwall's largest lake. Very little of the Loe Bar shingle is locally derived (compared with nearby Gunwalloe beach material to the south) and the deposits have been tentatively dated as Eocene. The composition of the bar deposits are: chalk flint 86%, quartz 9%, grit 2.6%, greensand chert 2% and serpentine 0.5%. The shingle coming from drowned terraces of the former river that flowed down the English Channel; the nearest onshore source is 120 miles (190 km) away in East Devon. Longshore drift is unlikely to have caused the formation because the bar is situated between two headlands but it plays an important part in the maintenance of the bar, with a strong current flowing to the south-east from Porthleven to Gunwalloe, depositing shingle along the bar. The ebb flow is not a simple reverse flow and is not strong enough to remove all the deposits.
Marine Conservation Zone
The Mounts Bay Marine Conservation Zone (MCZ) was designated on 29th January 2016 and covers an area of Mount’s Bay south of the coast from Long Rock to Cudden Point. The 12 km² site includes the sea around St Michael’s Mount and tidal reefs such as the Greeb, near Perranuthnoe, and the Long Rock. The MCZ protects habitats ranging from exposed high-energy rock on the coast to sand and muddy sand on the sea floor. The seagrass beds, Zostera marina, mainly grow in the sub-tidal zone and are important as a nursery area for fish and shellfish, as well as a feeding area for birds. Damage from the anchors and chains from moored boats can damage the beds.
In August 1625 "Turks took out of the church of Munigesca in Mount's Bay about sixty men, women and children and carried them away captives". Slavery in the Ottoman Empire and the Barbary slave trade was fundamental to its economy. The Barbary Pirates were then raiding Europe and they took more than a million Europeans off to the slave markets of Tripoli and elsewhere.
On 1 November 1755, the Lisbon earthquake caused a tsunami to strike the Cornish coast at around 14:00. At Mount's Bay the sea rose ten feet at great speed and ebbed at the same rate. Little damage was recorded. It was possibly this tsunami that removed Porth Plement, one of the five ports of St. Michael's Mount, but not the oldest which was Marazion.
There are several coastal towns and villages dotted around Mount's Bay of which the largest is Penzance. To the west are Newlyn, Paul, Mousehole and Lamorna. and to the east are Marazion, Perranuthnoe, Praa Sands, Porthleven and Mullion. The bay also incorporates many beaches, coves and features including Prussia Cove, Loe Pool (and Loe Bar), Church Cove, Poldhu Cove and Kynance Cove.
Mount's Bay gives its name to a local secondary school, which is located in Heamoor and serves Penzance and the surrounding countryside. Mount's Bay School and Community Sports College (formerly Heamoor Secondary Modern School ) is one of Penzance's comprehensive schools.
RFA Mount's Bay
Commissioned by the Royal Fleet Auxiliary in 2006, RFA Mount's Bay is the latest-design Landing Ship Dock, the Bay Class used by the Royal Navy. Mount's Bay has good affiliations with the Sea Cadet Unit TS Zephyr in Caterham, Surrey.
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