This Earth Cache is on the route when doing either the Harkerville 2 day hike, or the Kranshoek 1 day trail.
It is not nesecary to do either though, and can be accessed from the parking, walking down the hill, getting your answers, and walking back up. There is a small conservation fee payable at the entrance gate, Wild Card holders enter free.
A shingle beach is a beach which is armoured with pebbles or small- to medium-sized cobbels (as opposed to fine sand). Typically, the stone composition may grade from characteristic sizes ranging from two to 200 mm diameter. A pebble is a clast of rock with a particle size of 2 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter).
While this beach land form is most commonly found in Western Europe, examples are found in a number of other world regions, such as the east coast of New Zealand's South Island, where they are associated with the shingle fans of braided rivers. Shingle beaches are typically steep, because the waves easily flow through the coarse, porous surface of the beach, decreasing the effect of backwash erosion and increasing the formation of sediment into a steeply sloping beach.
Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, they can have marks of contact with other rocks or other pebbles. Pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with seawater.
Beaches composed of pebbles and other larger materials are usually described as intermediate or reflective beaches. They usually have a steep offshore slope and are narrow and steep in relief. Waves are either 'collapsing' or 'surging' in character with a strong swash and weak backwash. Hence larger pebble material is driven onshore under a strong swash and then deposited as the backwash is too weak to remove it. Also, on pebble beaches quite a bit of energy in the backwash will be lost via percolation (usually 33-50%) which further weakens the backwash.
There are many places where there are no pebbles available, so sand is the only material that can make the beach. These sediments come from broken rock somewhere, either on sea cliffs or coming down rivers. Once they get to the shore line area they are moved along the shore by wave action and tend to break down over time. So if the sediment source is far away or does not have any pebble size material there will be none on the beach.
The other thing is that when both sizes of material are available, the one that will be on the beach depends on the strength of the wave action. Strong waves will be able to move big rocks and pebbles up onto the beach and carry the smaller sand grains away into the deeper water. But if the wave action is not as strong it will only be able to move the sand grains up onto the beach, and that is what you will find.
Generally, when there is a shoreline that faces out onto rough water with big waves, it will be eroding back and producing larger sized material that stays on the beach. Shorelines facing calmer waters will have sand.
ABOUT THIS LOCATION:
Quartz, the second most common material occurs as seams and cobble inclusions within the Table Mountain Sandstone quartzite, and also some quartzitic sandstone, conglomerate and shale strata, that is the parent materials of the pebbles, cobbles and boulders found here.
You will notice that this beach is continually "worked" by the sea. No vegetation can take hold on it. The best time to observe the tremendous power of the sea and its effects on the shore, is during a Winter storm. Rolling clasts (pebbles, cobbles and boulders) "chatter" as the surge move them forward and backwards. The sound at this beach is quite something to hear as this phenomena takes place, as this beach is more than 300 meters long covered in clasts.
You will also notice that the clasts on the beach is rounded to well rounded by the energy of the sea. The clasts in the river flowing into the sea here is not nearly as rounded as the clasts on the beach. The energy potential of the sea is obviously much stronger than that of the river.
To claim this cache, please send me a email or message through my profile with answers to the following questions:
1) In your opinion, how are Shingle beaches formed?
2) Would you say the sea is normally calm or strong here?
3) At the coordinates you will find a sign, indicating this to be a pebble beach. Noting the average size of the material on the beach, do you agree with this sign? Qualify your answer.
4) Optionally, it would be appreciated if you can upload a photo taken during your visit.
REFERENCES:
https://en.wikipedia.org/wiki/Shingle_beach
https://en.wikipedia.org/wiki/Pebble
http://www.thestudentroom.co.uk/showthread.php?t=630043
https://answers.yahoo.com/question/index?qid=20090214212410AA2CsmT
