Forgotten Dunes EarthCache
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Located in the dunes above the picturesque Hout Bay town. Some stunning views of the mountains and seas are available in and around Hout Bay – with plenty of caching opportunities too.
Hout Bay is located in the bay on the northern end of the famous Chapman’s Peak Drive. This goes from Noordhoek along a toll road into the little village of Hout Bay (meaning Wood Bay). Chapman’s Peak Drive takes you along a major unconformity for a number of kilometres along the route. An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record. The Cape Granite is for the most part below the road. Looking across the bay from this cache – you should clearly make out the lower greys of the granites and the upper sandstones and quartzites of the Table Mountain suite.
Hout Bay itself, was once known for its manganese mine (see the nearby cache and Leopard statue too) which closed in 1911. Manganese oxides occur as thin, vein-like deposits in zones of fracturing in the Table Mountain sandstone. Ore was exported by sea from the local jetty in the harbour. The concrete pillars of this original jetty can be seen on the coast near the Flora Bay Resort.
This cache site marks an area of sand that was blown off the wide beaches by wind. These are the remnants of the old sand dunes. However, short-sighted human intervention and development has created artificial barriers (roads, buildings, fences, trees, gardens etc, and has all but stopped the natural movement of the sand from the bay up to the “nek” between the Sentinal and Mount Rhodes and then on downwards to the beaches to the north. It has been surmised, that this may have been a primary sand feed for beaches as far north as Clifton (part of Cape Town). Unless remedial action is taken, and the supply of sand is restored, these beaches between cape Town and Llandudno face the prospect of becoming rockier and rockier over time.
(Acknowledgments: Geological Journeys.; Norman & Whitfield; 2006).
This dune system has also been referred to a “headland bypass dune”. If you go onto Google Earth and look at this cache location – then zoom up to about 4.5 km about sea level – you can see the path of the dunes fairly clearly.
In order to qualify to log this cache, you need to answer the following questions and email the cache owner. Any logs not accompanied by an email will be deleted.
1) Take a photo of you and your GPSr at this spot with any nearby geological or dune feature (or marker) visible and include in your log. [Optional]
2) Explain what “long shore drift” is – and how it would move sand once in the sea.
3) Look around the town (driving or walking to the cache site – or along the harbour front) – explain some of the evidence that you see of sand being moved by wind. Photos are a great to record these..
4) Looking around the surrounding areas (especially across near Chapman’s Peak Drive) – which rocks do you think this sand originated from?
5) What do you think will happen in both this area – and on the beaches north of here – over time – assuming that the human development will not be knocked down – and the sand movement will continue to be blocked?
Additional Hints
(Decrypt)
Erzrzore gb fraq lbhe rznvy!