Cape Peninsula

From Wikipedia, the free encyclopedia
Jump to: navigation, search
The Cape of Good Hope; looking towards the west, from the coastal cliffs above Cape Point.
Map showing the Cape Peninsula, illustrating the positions of the Cape Town City Centre, Table Mountain, the main mountains and peaks that make up the Peninsula, and the Cape of Good Hope.

The Cape Peninsula (Afrikaans: Kaapse Skiereiland) is a generally rocky peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At the southern end of the peninsula are Cape Point and the Cape of Good Hope. On the northern end is Table Mountain, overlooking Cape Town, South Africa. The peninsula is 52 km long from Mouille point in the north to Cape Point in the south.[1]

The courses of the warm Agulhas current (red) along the east coast of South Africa, and the cold Benguela current (blue) along the west coast. Note that the Benguela current does not originate from Antarctic waters in the South Atlantic Ocean, but from upwelling of water from the cold depths of the Atlantic Ocean against the west coast of the continent. The two currents do not "meet" anywhere along the south coast of Africa.

The Peninsula has been an island on and off for the past 5 million years, as sea levels fell and rose with the ice age and interglacial global warming cycles of, particularly, the Pleistocene.[2] The last time that the Peninsula was an island was about 6000 years ago.[3] Soon afterwards it was joined to the mainland by the emergence from the sea of the sandy area now known as the Cape Flats. The towns and villages of the Cape Peninsula and Cape Flats now form part of the City of Cape Town Metropolitan Municipality.

The Cape of Good Hope is sometimes given as the meeting point of the Atlantic and Indian Oceans. Thus the west coast of the Peninsula is invariably referred to as the "Atlantic Coast",[4] but the eastern side is known as the "False Bay Coast". It is at Cape Point (or the Cape of Good Hope) that the ocean to the south is often said to be divided into the Atlantic Ocean to the west, and the Indian Ocean to the east. However, according to the International Hydrographic Organization agreement that defines the ocean boundaries, the meeting point is at Cape Agulhas, about 200 km (120 mi) to the southeast.[5][6]

Similarly, Cape Point is not the fixed "meeting point" of the cold Benguela Current, running northwards along the west coast of Africa, and the warm Agulhas Current, running south from the equator along the east coast of Africa. In fact the south flowing Agulhas Current swings away from the African coastline between about East London and Port Elizabeth, from where it follows the edge of the Continental shelf roughly as far as the southern tip of the Agulhas Bank, 250 km (155 miles) south of Cape Agulhas.[7] From there it is retroflexed (turned sharply round) in an easterly direction by the South Atlantic, South Indian and Southern Ocean currents, known as the "West Wind Drift", which flow eastwards round Antarctica. The Benguela Current, on the other hand, is an upwelling current which brings cold, mineral-rich water from the depths of the Atlantic Ocean to the surface along the west coast of Southern Africa. Having reached the surface it flows northwards as a result of the prevailing wind and Coriolis forces. The Benguela Current, therefore, effectively starts at Cape Point, and flows northwards from there,[7][8] although further out to sea it is joined by surface water that has crossed the South Atlantic from South America as part of the South Atlantic Gyre.[8] Thus the Benguela and Agulhas currents do not strictly "meet" anywhere, although eddies from the Agulhas current do from time to time round the Cape to join the Benguela Current.[7][8]

Ecology[edit]

Table Mountain National Park, previously known as the Cape Peninsula National Park, was proclaimed on 29 May 1998, for the purpose of protecting the natural environment of the Table Mountain Chain, and in particular the rare fynbos vegetation. The park comprises a large part of the undeveloped area of the Cape Peninsula, and is managed by South African National Parks Board. The coastal waters surrounding the Cape Peninsula are proclaimed as a Marine Protected Area since 2004, and include several no-take zones, and are part of the National Park. The waters of this marine protected area are unusual in that they are parts of two fairly distinct marine bioregions, namely the Agulhas Bioregion and the South-western Cape Bioregion. The boundary is at Cape Point.

Flora[edit]

A King protea growing in Peninsula Sandstone Fynbos on Table Mountain
Silver trees (Leucadendron argenteum) only occur naturally on the granite and clay soils of the Cape Peninsula, surrounding Table Mountain and the Back Table.[9][10] A few tiny patches, possibly planted there by early European settlers, occur near Stellenbosch, Paarl and Somerset West.[9] This photo was taken on Lion's Head, looking towards the Twelve Apostles.
The Disa uniflora, also known as the Pride of Table Mountain is a showy orchid that blooms under waterfalls, along streamlets and seeps on the top and upper slopes of Table Mountain and the Back Table, in January-March.[11]
Indigenous forest on Table Mountain, with Devils Peak visible in the distance

The Cape Peninsula has an unusually rich biodiversity. Its vegetation consists predominantly of several different types of the unique and rich Cape Fynbos. The main vegetation type is endangered Peninsula Sandstone Fynbos, but critically endangered Peninsula Granite Fynbos, Peninsula Shale Renosterveld and Afromontane forest occur in smaller portions on the mountain ranges of the Peninsula. On the sandy Cape Flats lowlands there are a few pockets of protected Cape Flats Sand Fynbos.

The Peninsula's vegetation types form part of the Cape Floral Region protected areas. These protected areas are a World Heritage Site, and an estimated 2,200 species of plants are confined to Table Mountain range - which are at least as many as occur in the whole of the United Kingdom.[12][13] Many of these species, including a great many types of proteas, are endemic to these mountains and can be found nowhere else. The Disa uniflora, despite its restricted range within the Western Cape, is relatively common in the perennially wet areas (waterfalls, streamlets and seeps) on Table Mountain and the Back Table, but hardly anywhere else on the Cape Peninsula.[11][14] It is a very showy orchid that blooms from January to March on the Table Mountain Sandstone regions of the mountain. Although they are quite widespread on the Back Table, the best (most certain, and close-up) place to view these beautiful blooms is in the "Aqueduct" off the Smuts Track, halfway between Skeleton Gorge and Maclear's Beacon.

Remnant patches of indigenous forest persist in the wetter ravines. However, much of the indigenous forest was felled by the early European settlers for fuel for the lime kilns needed during the construction of the Castle.[15] The exact extent of the original forests is unknown, though most of it was probably along the eastern slopes of Devil's Peak, Table Mountain and the Back Table where names such as Rondebosch, Kirstenbosch, Klassenbosch and Witteboomen survive (in Dutch "bosch" means forest; and "boomen" means trees) . Hout Bay (in Dutch "hout" means wood) was another source of timber and fuel as the name suggests.[15] In the early 1900s commercial pine plantations were planted on these slopes all the way from the Constantiaberg to the front of Devil’s Peak, and even on top of the mountains, but these have now been largely cleared allowing fynbos to flourish in the regions where the indigenous Afromontane forests have not survived, or never existed.

Fynbos is a fire adapted vegetation, and evidence suggests that in the absence of regular fires all but the drier fynbos would become dominated by trees.[12] Regular fires have dominated fynbos for at least the past 12 000 years largely as a result of human activity,[13][16] originally probably to maintain a productive stock of edible bulbs and to facilitate hunting, and later, after the arrival of pastoralists,[17] to provide fresh grazing after the rains.[16] Thus the plants that make up fynbos today are those that have been subjected to a variety of fire regimes over a very long period time, and their preservation now requires regular burning. The frequency of the fires obviously determines precisely which mix of plants will dominate any particular region,[18] but intervals of 10-15 years between fires[12] are considered to promote the proliferation of the larger Protea species, a rare local colony of which, the Aulax umbellata (Family: Proteaceae), was wiped out on the Peninsula by more frequent fires.[18] Some bulbs may similarly have become extinct as a result a too rapid sequence of fires.[18] The fires that occur on the mountains today are still largely due to unregulated human activity. Fire frequency is therefore a matter of chance rather than conservation.

Despite intensive conservation efforts the Table Mountain range has the highest concentration of threatened species of any continental area of equivalent size in the world.[12][19] The non-urban areas of the Cape Peninsula (mainly on the mountains and mountain slopes) have suffered particularly under a massive onslaught of invasive alien plants for well over a century, with perhaps the worst invader being the cluster pine, partly because it was planted in extensive commercial plantations along the eastern slopes of the mountains, north of Muizenberg. Considerable efforts have been made to control the rapid spread of these invasive alien trees. Other invasive plants include Black Wattle, Blackwood, Port Jackson and Rooikrans (All Australian members of the Acacia family), as well as several Hakea species and Bramble.[12][18][20]

The Cape hyrax or "dassie" as it is known in South Africa. It is the Verreaux's eagle's favourite and almost exclusive prey.

Fauna[edit]

The most common mammal on the mountains was the dassie, or rock hyrax. Between about 2000 and 2004 (no one is certain about the exact year or years) their numbers suddenly plummeted for unknown reasons. They used to cluster around the upper cable station on Table Mountain, near areas where tourists discarded or (illegally) supplied food. The population crash of the dassies has in all probability been responsible for the decline in the Verreaux's eagle population on the Peninsula. From 2004 (when monitoring was re-initiated) till 2012 there was only one nesting pair on the cliffs below Noordhoek Peak, (and since then only a single individual), when previously there had been at least three pairs, one of which had a cliff nest near the upper cable station on Table Mountain, in Blinkwater Ravine. Dassies were an important part the Verreaux's eagle's prey on the Peninsula.[21] Table Mountain is also home to porcupines, mongooses, snakes, lizards, tortoises, and a rare endemic species of amphibian that is only found on Table Mountain, the Table Mountain ghost frog. The last lion in the area was shot circa 1802. Leopards persisted on the mountains until perhaps the 1920s but are now extinct locally. Two smaller, secretive, nocturnal carnivores, the rooikat (caracal) and the vaalboskat (also called the vaalkat or African wild cat) were once common in the mountains and the mountain slopes. The rooikat continues to be seen on rare occasions by mountaineers but the status of the vaalboskat is uncertain. The mountain cliffs are home to several raptors species, apart from the Verreaux's eagle. They include the jackal buzzard, booted eagle (in summer), African harrier-hawk, peregrine falcon and the rock kestrel.[21] There are currently (2014) four pairs of African fish eagles on the Peninsula, but they nest in trees generally as far away from human habitation as is possible on the Peninsula.

Up until the late 1990s baboons occurred on all the mountains of the Peninsula, including the Back Table immediately behind Table Mountain. Since then they have abandoned Table Mountain and the Back Table, and only occur on the Constantiaberg, and the mountains to the south. They have also abandoned the tops of many of the mountains, in favour of the lower slopes, particularly when these were covered in pine plantations which seemed to provide them with more, or higher quality food than the Fynbos on the mountain tops. However these new haunts are also within easy reach of Cape Town's suburbs, which brings them into conflict with humans and dogs, and the risk of traffic accidents. There are now (2014) a dozen troops on the Peninsula, varying in size from 7 to over 100 individuals, scattered on the mountains from the Constantiaberg to Cape Point.[22][23] The baboon troops are the subject of intense research into their movements (both of individuals and of the troops), their physiology, genetics, social interactions and habits. In addition, their sleeping sites are noted each evening, so that monitors armed with paint ball guns can stay with the troop all day, to ward them off from wandering into the suburbs. From when this initiative was started in 2009 the number of baboons on the Peninsula has increased from 350 to 450, and the number of baboons killed or injured by residents has decreased.[23]

Rau quagga in the animal camp on the slopes of Devil’s Peak, above Groote Schuur Hospital.

Himalayan tahrs, fugitive descendants of tahrs that escaped from Groote Schuur Zoo near the University of Cape Town, in 1936, used to be common on the less accessible upper parts of the mountain. As an exotic species, they were almost eradicated through a culling programme initiated by the South African National Parks to make way for the reintroduction of indigenous klipspringers. Until recently there were also small numbers of fallow deer of European origin and sambar deer from southeast Asia. These were mainly in the Rhodes Memorial area but during the 1960s they could be found as far afield as Signal Hill. These animals may still be seen occasionally despite efforts to eliminate or relocate them.

On the lower slopes of Devil’s Peak, above Groote Schuur Hospital an animal camp bequeathed to the City of Cape Town by Cecil John Rhodes has been used in recent years as part of the Quagga Project.[24] The quagga used to roam the Cape Peninsula, the Karoo and the Free State in large numbers, but were hunted to extinction during the early 1800s. The last quagga died in an Amsterdam zoo in 1883. In 1987 a project was launched by Reinhold Rau to back-breed the quagga, after it had been established, using mitochondrial DNA obtained from museum specimens, that the quagga was closely related to the plains zebra, and on 20 January, 2005 a foal considered to be the first quagga-like individual because of a visible reduced striping, was born. These quagga-like zebra are officially known as Rau quagga, as no one can be certain that they are anything more than quagga look-alikes. The animal camp above Groote Schuur Hospital has several good looking Rau quaggas, but they are unfortunately not easily seen except from within the game camp, which is quite large and undulating, and the animals are few. The animal camp in not open to the public.

Geology[edit]

See also: Cape Fold Belt
Geology of the Cape Peninsula, showing the where the Malmesbury Group and Cape Granite rocks and weathered soils are exposed, and overlain by the Cape Supergroup. The hard, erosion resistant Cape Supergroup form the mountains of the Peninsula.
Schematic West-East geological cross section through the Cape Peninsula to illustrate its general structure. It closely resembles a W-E section through the Back Table, immediately south of Table Mountain, but is not to scale. The height of the "plateau" varies from 1000 m on Table Mountain, in the north, to about 150 m close to Cape Point, 50 km to the south. The colour-coding is the same as on the geological map on the left. Kirstenbosch Botanical Gardens, and all the major wines estates on the Peninsula are situated on the fertile (weathered) granite slopes on the east side of the mountain.
A view of the cutting at the second hairpin bend on Ou Kaapse Weg, as it winds on to the Silvermine Plateau. The transition between the lowermost layer of the Table Mountain Group on the Cape Peninsula - the Graafwater Formation - and the layer above it, the Table Mountain Sandstone or Peninsula Formation, can be clearly seen. The photograph was taken at an elevation of 250 m.
A view of the eastern crags (or cliffs) of Table Mountain and Devils Peak as seen from Newlands Forest, above the University of Cape Town. The two layers of the Table Mountain Group which are represented on the Cape Peninsula, namely the Graafwater Formation and the Table Mountain Sandstone or Peninsula Formation, can readily be distinguished. The remaining layer, the Pakhuis Formation, occurs as a tiny remnant at Maclear's Beacon on the top of Table Mountain, not visible in the photograph. The granite basement on which the Table Mountain Group rests on the Cape Peninsula is obscured by the forest in the foreground.
An west-east (left to right) geological cross section through Table Mountain on the Cape Peninsula, the Cape Flats (the isthmus connecting the Peninsula to the African mainland) and the Hottentots-Holland Mountains on the mainland. It indicates how the Cape Fold Mountains have been eroded in this region, leaving what was once the bottom of a valley to form Table Mountain with its flat table-top structure.[2]

The Cape Peninsula is underlain by the oldest rocks in the area, the Malmesbury Group, and the granite intrusions of the Peninsula pluton.

The Malmesbury Group has been dated from between 830 and 980 Mya, and was deformed during the Saldanian orogenic cycle, both before and during the granite intrusions of 630 to 500 Mya, and there are minor intrusions which precede the granite. The base of this group has not been exposed.[25] The basal rocks were eroded to a relatively featureless peneplain with exposed granites covering most of the peninsula south of Lion's Head and Devil's Peak. The Sea-Point contact zone, described by Charles Darwin is a well known region of metamorphic rocks formed by the (originally very hot) granite intrusion into the Malmesbury rocks.[2]

These rocks were later unconformably covered by the Cape Supergroup. The Cape Supergroup is divided into eight formations, the three oldest of which are present on the Peninsula. The lowest present is the reddish Graafwater formation which consist of shales and sandstone. The Graafwater Formation can be clearly seen in the cutting on the second hairpin bend as the Ou Kaapse Weg (road) goes up the slope from Westlake on to the Silvermine plateau. In the cutting one can also see the abrupt and obvious transition into the Table Mountain Sandstone (or, as it is currently known, the Peninsula Formation Sandstone) above it. Looking up the slope from below to the first hairpin bend, the granite basement on which the Graafwater formation rests is visible. And in the cutting at the first hairpin bend, the ocher-colored, gritty clay into which the granite weathers is clearly displayed. The relatively thin Graafwater layer (no more than about 60-70 m thick on the Cape Peninsula) is overlain by the prominent Peninsula Formation, which consist mainly of hard, erosion resistant, quartzitic sandstone, which form the high, prominent, almost vertical cliffs of the Cape Peninsula. At the very top of Table Mountain, at Maclear's Beacon, is a small remnant of the Pakhuis Diamictites, better represented in the Cederberg Mountains, 200 km to the north of Cape Town .[25]

References[edit]

  1. ^ 1:250,000 Geological Series map 3318:Cape Town, Government Printer, Pretoria, 1990.
  2. ^ a b c Compton, John S. (2004) The Rocks & Mountains of Cape Town. Cape Town: Double Story. ISBN 978-1-919930-70-1
  3. ^ Parkington John (2006). Shorelines, Strandlopers and Shell Middens. p. 69. DTP & Production: Neil Rusch Southern Cross Ventures, Kenilworth, Cape Town.
  4. ^ http://www.discoverthecape.com/atlantic-coast.html
  5. ^ http://ioc.unesco.org/oceanteacher/OceanTeacher2/01_GlobOcToday/03_GeopolOc/s23_1953.pdf
  6. ^ http://www.southafrica.info/about/geography/oceansmeet.htm
  7. ^ a b c Branch, M & Branch G. (1981). The Living Shores of Southern Africa. pp. 14-18. Struik Publishers, Cape Town.
  8. ^ a b c Tyson, P.D., Preston-Whyte, R.A. (2000) The Weather and Climate of Southern Africa. pp. 221-223. Oxford University Press, Cape Town
  9. ^ a b Manning, John (2007). "Cone Bush, Tolbos". In: Field Guide to Fynbos. Cape Town: Struik Publishers. p. 258. ISBN 9781770072657. 
  10. ^ http://www.proteaatlas.org.za/cpldarge.htm
  11. ^ a b Trinder-Smith, Terry (2006). "Orchidaceae". In: Wild Flowers of the Table Mountain National Park. Kirstenbosch, Claremont: Botanical Society of South Africa. p. 104-105. ISBN 1874999600. 
  12. ^ a b c d e Manning, John (2007). "The World of Fynbos". In: Field Guide to Fynbos. Cape Town: Struik Publishers. pp. 8–23. ISBN 9781770072657. 
  13. ^ a b Trinder-Smith, Terry (2006). "Introduction". In: Wild Flowers of the Table Mountain National Park. Cape Town: Botanical Society of South Africa. pp. 19–35. ISBN 1874999600. 
  14. ^ Manning, John (2007). "Disa". In: Field Guide to Fynbos. Cape Town: Struik Publishers. pp. 162–163. ISBN 9781770072657. 
  15. ^ a b Sleigh, Dan (2002). Islands. London: Secker & Warburg. p. 429. ISBN 0436206323. 
  16. ^ a b Kraaij, Tineke; van Wilgen, Brian W. (2014). "Drivers, ecology, and management of fynbos fires.". In Allsopp, Nicky; Colville, Jonathan F.; Verboom, G. Anthony. Fynbos, Ecology, Evolution and Conservation of a Megadiverse Region. Oxford: Oxford University Press. p. 47. ISBN 9780199679584. 
  17. ^ Saunders, Christopher; Bundy, Colin (eds.), eds. (1992). "A way of life perfected". Readers’ Digest Illustrated History of South Africa. Cape Town: Reader’s Digest Association Ltd. pp. 20–25. ISBN 0-947008-90-X. 
  18. ^ a b c d Maytham Kid, Mary (1983). "Introduction". In: Cape Peninsula. South African Wild Flower Guide 3. Kirstenbosch, Claremont: Botanical Society of South Africa. p. 27. ISBN 0620067454. 
  19. ^ "Perceval". 
  20. ^ "Brochures, booklets and posters". Capetown.gov.za. Retrieved 2013-01-12. 
  21. ^ a b Hockey, P. A. R.; Dean, W. R. J.; Ryan, P. G., eds. (2005). Roberts Birds of Southern Africa (Seventh ed.). Cape Town: John Voelcker Bird Book Fund. pp. 531–532. ISBN 0-620-34053-3. 
  22. ^ http://www.baboonsonline.org/bru/ Cape Peninsula Baboon Research Unit
  23. ^ a b http://www.ncc-group.co.za/case-studies/managing-baboon-human-conflict-city-cape-town Managing Baboon-human conflict: City of Cape Town
  24. ^ http://www.quaggaproject.org/ The Quagga Project South Africa
  25. ^ a b Theron, J.N. Gresse, P.G. Siegfried, H.P. and Rogers, J. Explanation sheet 3318 – The Geology of the Cape Town Area. Geological Survey, Department of Mineral and Energy Affairs, Government Printer, Pretoria 1992. ISBN 978-0-621-14284-6

Coordinates: 34°12′18″S 18°24′14″E / 34.205°S 18.404°E / -34.205; 18.404