Difference between revisions of "Diving the Cape Peninsula and False Bay/Star Wall"
Revision as of 07:42, 7 January 2012
The dive site Star Wall or Star Walls is an offshore rocky reef wall south west of Duiker Point in the Karbonkelberg headland area on the Atlantic seaboard of the Cape Peninsula, near Cape Town in the Western Cape province of South Africa.
This site was first recorded in March 2006. It is the tallest and longest wall known in the Cape Town area and is a dive site well worth visiting, with a wide range of interesting and colourful invertebrates and spectacular topography, both on the wall itself an on the adjacent reef to the north.
S34°02.466' E18°18.087' (Shallowest point)
About 200m roughly south west of the offshore rock at Duiker Point.
This site is in a Marine Protected Area (2009). A permit is required. The site is entirely within the Karbonkelberg Restricted Area.
The name "Star Walls" was probably chosen with reference to the adjacent site "Kanobi's Wall", as an allusion to the movie series "Star Wars", and to the vertical granite cliff face that constitutes the site. The site was discovered and named by BlueFlash charters in 2006.
Maximum depth at the base of the wall is 32m, and the top of wall is at approximately 8m. The pinnacle on top of the rock is at about 5m
Visibility is variable, as with all sites in the region. On a really good day it may exceed 20m, and will then usually be very cold. These conditions normally occur in summer, when upwellings driven by the strong south easterly winds bring cold, clear, deep water to the surface. The good visibility does not often last long, and is usually followed by a plankton bloom soon after the wind dies down. More often the visibility is less than 10m, and it is quite commonly around 5 to 8m in ordinary diving conditions. Of course it can easily be worse, and may be as low as 3 or 4m, even if the conditions otherwise look good. This means that you just have to look at the critters, and for this a light is useful.
Star Wall is a massive and continuous almost vertical granite wall of about 25m height, extending for a length of approximately 100m west to east on the south face of an enormous outcrop, with an extra 50m length of wall on the south-east face. The bottom of the wall is on sand patches amongst large boulders and relatively low outcrops further to the south. The western end of the wall makes a sharp turn towards the north, and the top is deeper in this area. The rock of the wall is fractured by a number of joints which have weathered to form crevices and small undercuts. These joints are mostly vertical and horizontal, and a few are fairly deeply indented, providing more protected local micro-environments, and which typically are more heavily encrusted with invertebrates.
The wall is the south and deepest face of a huge outcrop, and the north side is more indented and broken up, and slopes down less steeply, to a depth of between 15 and 21m. There are several small caves and swimthroughs in this area, and though there is no massive wall, the topography is varied and complex, with large boulders, gullies, crevices and overhangs. The reef is continuous to Kanobi's wall to the north, with a number of high pinnacles, some of which are shown on the map.
South of the wall the reef is much lower in profile, though there is an outcrop several metres high quite near to the eastern end of the wall.
The south east face is also a wall, and is separated from a somewhat lower outcrop by a fairly narrow gully with a slightly shallower bottom, which slopes up to the north east, then forks into several gullies.
Somewhat to the north east of the wall there is a cave swimthrough large enough to turn a scooter inside. The position is shown on the map as M&M cave, which is the initials of the divers who found it and marked its position. They also reported a long swimthrough quite nearby, but the exact position is not known.
Geology: Granite of the late Pre-Cambrian Peninsula pluton.
Surge — The site is exposed to south westerly swells, which can produce a strong surge over the top of the wall and pinnacles, some of which may break in moderate seas. Surge is usually much weaker in deeper areas, particularly on the face of the wall, which lies across the wave fronts of the prevailing swell.
Currents — At times there is a slight current along the wall, which has been known to run opposite to the prevailing south easterly wind. Currents may also develop across the wall, over the reef, probably due to local winds, as they are short lived and unpredictable, and progress against the current will be relatively strenuous, but the main strength of the current is usually at the surface and down on the reef it is usually much weaker. It can be quite tricky to pick up divers from the water if the swell picks up during the dive, specially if the wind or current is setting you onto the blinders at Kanobi's reef to the north. A current of approximately 1km/h setting magnetic south has been measured on a day of light south eaterly to easterly wind, and two days later a north setting current of similar strength, also with a south easterly wind.
Temperature — The water will usually be cold. Temperatures are generally 12°C or less, but have not been recorded lower than 8°C. 14°C would be considered unusually warm. A thermocline of one or two degrees may occur, and this is often associated with a change in visibility.
Seasonal variations — Conditions suitable for diving this site will be most common in summer, but any time when the south westerly swell is weak and low may be suitable, though visibility may be more unpredictable in winter.
Upwellings and plankton blooms — This is an area which sometimes has upwellings, caused by the south easterly wind, which generally bring in cold, clear, nutrient rich bottom water. This will usually develop a plankton bloom over a day or two of good sunshine, which will reduce shallow water visibility again. This means that the best times to dive are during or directly after an extended period of moderate to strong south easterly winds, and this generally happens in summer. A plankton bloom which reduces surface visibility to 2 to 5m may well only extend down a moderate distance, and the visibility below will usually be better. The depth of the bloom is unpredictable and may range from around 5 or 6m to about 20m. Light levels below the bloom are often drastically reduced, and the colour tends to be very green.
The site can only be accessed by boat. It is about 6.6 km from Hout Bay harbour.
Typical of the big reefs of the Atlantic coast. Heavy growth of red bait and kelp on top. Walls, crevices and overhangs are covered with a large variety of sponges, corals, ascidians and other sessile invertebrates, and a host of small mobile critters, many of them well camouflaged.
There is a marked difference between the benthic ecology on the more vertical parts of the reef and the flatter areas. The walls and slight overhangs in the 12m to 24m range probably have the most diverse invertebrate cover, and certainly the most colourful. There are large numbers of small gorgonian sea fans, noble corals, soft corals, hydroids, anemones, sponges, colonial ascidians, and bryozoans, providing shelter and food for more mobile invertebrates, The predominant colours are oranges and browns, with splashes of bright blues, yellows, pinks and an occasional touch of green. The depth range from about 15 to 21m is probably the most colorful.
The high parts of the reef tend to be covered by extremely dense cover of the solitary ascidian Pyura stolonifera, commonly known as Red Bait, and much of the flatter surface above 15m has split-fan kelp forest. The deeper flattish surfaces are relatively sparsely covered, with sea cucumbers and sea urchins as the more obvious cover, and a variety of encrusting sponges and coralline algae
The Sumo crab which often carries a "hat" of the Green-moon sponge has frequently been seen on the wall.
The longest and highest unbroken wall dive known in the Cape Peninsula. It is about as high as a 7 floor building and longer than a football field. There are a few small cave/swimthroughs to the north of the outcrop, and a larger cave to the north east.
This is a great site for invertebrate photography. Macro and wide-angle equipment are most suitable.
Find out which way the current is running (if any) and drop in on top of the wall. Swim over the edge and descend to the depth of your choice. Start deep and work your way up, inspecting the various zones and working your way along the face with the current. The site is quite long, and often dived without a shotline, as the surge on top of the reef can be rather strong, so a DSMB is useful to alert the boat to your position when ascending.
The site is in a very exposed area and one should not dive there if there is big swell or strong wind. Skippers beware of the pinnacle as it breaks unexpectedly if there is swell or a low tide. This is a particular problem when the swells are in "sets", as there may be a long period where the swells are low and well behaved, followed by a few big ones, which can lift and break without much warning, and can be quite stressful if the boat is over the top of the reef at the time.
For this reason it is quite common not to use a shotline. The wall is big and easy to find, and if the swell is marginal it is better to drop off the boat a short distance to the south of the wall to avoid the lumpy seas and strong surge on top. The wall is then found by simply descending to about 15m and swimming north. Ascent in these conditions is also safer if you swim away from the wall to the south before ascending on a DSMB
Other hazards are cold water and strong surge, especially around the pinnacle. Strong offshore winds may develop over a short time in summer, but these are usually forecast.
Ability to deploy a DSMB from mid-water is useful, good buoyancy control is essential.
A DSMB is useful if you surface away from the shot line or there is no shot line. Nitrox can significantly extend your dive time if you are well insulated, and a dry suit is recommended as the water will be cold. If you have a full face mask, it will help on the really cold days, but most divers just take a few minutes for their face to get used to the cold.