Pofadder is located in the Namakwa Region of the Northern Cape and has some interesting geological formations. Whether you arrive at this EarthCache from the west or the east you will have traveled through some diverse landscape – with more to come!
Your tasks – the C.S.I. work!
At GZ you will find dunes on either side of the road. These are of the very few inland dunes that you will find in South Africa and probably the only ones south of the Orange River.
In order to substantiate your visit and be able to claim this EarthCache a number of questions need to be answered and submitted to the cache developer, via e-mail, to “cincolcc [at] gmail.com”
1 – In your own words explain what type of dunes you are looking at here. This will require some internet research and no graphic examples have been placed in the description on purpose! Reading the above description could perhaps point you in the right direction though.
2 – Look at the dunes and explain the colouring and vegetation.
3 – Based on your answer above where do you think the sand came from and why did the dunes form here and not elsewhere? Why do you say this?
4 – Describe any other interesting things you saw or experiences you had on your journey to the site (you can add these to your log for others to enjoy too). Photos are always welcomed in the logs but please don’t post photos of the dunes themselves.
5 – At GZ you will see a small blue sign near the fence – what is written on the sign?
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.
Types of Sand Dunes
Sand dunes develop into all shapes and sizes, but that doesn't stop scientists from piling them into generalized categories. By using satellite and aerial photography of the world's deserts, the United States Geological Survey (USGS) has identified five types of sand dunes:
- The crescentic dune, also called the barchand dune, is the most common type of sand dune. As its name suggests, this dune is shaped like a crescent moon with points at each end, and it is usually wider than it is long. Crescentic dunes form when winds blow from one direction. This dune traverses desert surfaces faster than any other type of dune. The migrating dunes in China are crescentic dunes.
- The linear dune is straighter than the crescentic dune with ridges as its prominent feature. Unlike crescentic dunes, linear dunes are longer than they are wide -- in fact, some are more than 160km long. The ridges are long and snakelike, and these dunes usually occur in parallel sets separated by other sand, gravel or rocky corridors.
- The star dune has arms that radiate out from a centre pyramid-shaped mound, hence the descriptive name. Star dunes grow upward instead of outward and are a result of multidirectional winds. Common to the Sahara Desert, they tend to show up around topographic barriers. They're among the tallest sand dunes on Earth -- some star dunes in China are more than 500m tall.
- The dome dune is rare, oval- or circular-shaped and has no slip face. Dome dunes sometimes appear at the ends of crescentic dunes. Most dome dunes are low -- only a few feet high.
- The parabolic dune is U-shaped, but differs from the crescentic dune because its crests point upward, with elongated arms that follow behind. A parabolic dune's trailing arms are typically anchored by vegetation. The longest known parabolic dune has a trailing arm nearly 12km long.
Coastal sand dunes are a bit different from desert dunes. They form when an accumulation of sand blows inland from the beach. Coastal dunes always form in the predominant wind direction, but their shape and size depends on the shape of the beach. If a beach is shallow-sloped, more sand deposits on the shore, resulting in bigger dunes. On a steep beach, more sand washes back out to sea, and the dunes are smaller. Coastal dunes are a unique ecosystem, and they help to protect the surrounding area from erosion. Vegetation like dune grass acts as a stabilizer for coastal dunes.
Interestingly, scientists have recently confirmed the existence of sand dunes underwater, using advanced sonar equipment. Called sand waves, they can reach up to 210m long and more than 9m high. Changing tidal patterns, sediment and erosion help these underwater dunes to form.
Reference - http://geography.howstuffworks.com/terms-and-associations/sand-dune2.htm
