The background photo is showing a good example of this earth cache.

The aim of this very easy earth cache is to help you to understand the importance of the dunes in this area and why we should protect this environment. Many cachers have experienced the thrill to find the traditional cache at Gerickes point and I am sure that many had a good look at these dunes. On your way you will notice these huge sand dunes. Please note that the earth cache and the traditional cache are far away from each other to avoid confusion. Gerickes Point itself is a good example of this earth cache. What is the importance of these dunes and what have they in common with the various lakes in this area?

The biggest significance is that these are the highest fossil dunes in South Africa. These dunes were formed over 2 million years ago and they formed part of a series of dunes. On the south side of the dune you will find the Indian Ocean and on the north side you will find the coastal lake system. Sedgefield itself is bordered by a series of parallel fossil sand dunes. To the west of Sedgefield near Kaaimans River you will find the start of the sand dunes and it extends all the way to the east side of Sedgefield right up to Brenton on Sea. Over a period of time steep cliffs has formed, if you examine the dune you will note distinct layers and patterns which was formed by water, wind and sand erosion.

The sand dunes were formed during the Pleistocene period. During this period pieces of mollusc shell was mixed with the sand grains as the dunes were forming. With time rain water seeped through the sand and it dissolved the calcium carbonate of the shell fragments. It then percolated into the sand layer lower down. During periods of minimum disturbance to the dunes a layer of hard sand was formed. You can see the periods of minimum disturbances as layers in the dunes. A good example of these layers is at Myoli Beach and also on either side of Gerickes point. This is the timeline of Mother Nature you are looking at – she had 2 million years to form these dunes.

While you are studying the dunes you must also note the orientation of the dune. Here you can see the effect of a prevailing south westerly wind during these years.

The dune system consist of 3 fossil dune ridges it also called cordons. These three dunes run parallel to the coast line. The southern most dune is submerged today. This dune will be found about 2 miles out to sea and it formed a reef which used by scuba divers and fishermen. If you make use of Google Earth you will be able to see the reef.

The central dune runs along the coast line and is easy recognizable and it does reach a height of about 204 meters.

The third dune is also easy recognizable. But again, if you do not understand what you are looking at it will be easy to see a dune and not a system. With this information you will be able to understand a little bit more of this location. The third dune is easily seen as the cordon north of Groenvlei. Interesting enough there is also a remnant section in the west and this is the little island in Island Lake.

These dunes played a major role in forming the coastal lakes around the Sedgefield area and we have to explore this a little bit further. There is a term called marine regressions. During these regressions erosions were formed via flowing rivers which managed to cut through the younger geological dune formations. During these marine advances and regressions with the erosion of the soft geology and with the deposits of the sediments from the river platforms were build. At the end depressions were formed which was later filled with water and lakes were formed. Here the result of a combined climatic change can be seen on soft geology. The only other area where this phenomenon can be observed is between St Lucia and Ponta de Oura.

While you are studying these dunes you will also see another effect and end result namely the effect of erosion and the effect of such on the angle of repose. While walking to Gerickes Point you will see massive dune slips. Complete sections of dunes are breaking free continuously. This can be observed at Myoli dunes as well as at Brenton on Sea. The sea is undercutting the base of the dunes and it forms impressive cliffs. Originally this was a dune with a gradual sloping side but with time and the constant erosion impressive cliffs were formed.

On your way to Gerickes point you will find at various locations a red/brown layer of about 1.5 meters thick at the bottom. This layer varies all the time in height above sea level. The significance of this layer is that this is the sediment layer which was deposited on top of the existing foundation of the sand dune during that period.

Requirements to log the cache:

A. Physically challenged persons:

If you are physically challenged and you can not do the 2 km walk along the beach but would love to do this earth cache then it is possible to park very close to the dunes and to observe them from a distance via binoculars. Waypoint is given on listing. To log this cache email the cache owner with the answer to the question below. Please do not include any answers in your log. Please include a photo of your team with your log on the listing.

B. All other cachers

There is no physical cache container. Please do not abuse option A. To log this cache email the cache owner with the answer to the question below. Please do not include any answers in your log. Please include a photo of your team next to one of the features described in the listing or something that you have learned or observed which relates to earth caching. A photo at the waypoint with your team with Gerickes point visible in the background is also good.(This is an optional request and not a requirement to log).

Questions:

• Question 1: What is meant by “angle of repose” and how does it relate to the sand dune? This question is optional as this was not discussed.
• Question 2: During what geological time period did these dunes started to develop?
• Question 3: Explain the layering effect found in these dunes?

Recognitions and references:

• Photo belongs to “The Huskies”.
• Article and info: - Sedgefield Tourism Office.
• Mark Dixon from Garden Route Trail.

FTF Honours:
• Platinum: kiepie&kanders
• Gold: OLLIE.Q
• Silver: battlerat and pussycat
• Bronze: iPajero

Risk and Hazards (1 is low, 3 is average, 5 is extreme):
• Mist - 3
• Heights and falls: 3
• Lightening - 3
• Slipping - 3
• Strong winds - 3
• Wet weather - 3
• Snakes - 1
• Spiders - 1
• Muggles and muggers- 2
• Night Time - 4 (Not safe and you have to leave your vehicle, but can be done)
• Roads - 3
• Children - 3
• Thorns & Blackjacks - 1