TO QUALIFY TO LOG THIS CACHE you need to answer the following questions in an email to the cache owner via our profile on the geocaching website. Any logs not accompanied by an email will be deleted. The coordinates will take you to the side of the Storms River gorge at the start of the bridge. Take a walk out onto the bridge to answer the four questions.
1. How deep do you estimate the Storms River gorge is?
2. Looking down, how wide is the river?
3. The gorge looks like it does because the surrounding rock is quartzitic sandstone of the Table Mountain Formation. What do you think the gorge would have looked like if the rock was softer sandstone instead?
4. How does the rock go from normal or softer sandstone to the metamorphic quartzite sandstone that the rock in the gorge is made of?
As an additional (although not compulsary it will be appreciated) task, please take a selfie either on the bridge or with the bridge in the background and upload it with your log.
Storms River
The Storms River has a steep, mountain stream gradient over most of its course, that has helped it to cut its magnificent gorge. In addition it happened to strike a convenient weak zone to use as a bed. It's water flows vigorously and turbulently, especially during floods, which helps the erosive work. The near-vertical side walls of the Storms River gorge are a testimony to the hardness of the Table Mountain Quartzite (the quartzitic sandstone of the Table Mountain Formation - TMQ), as well as an indication of the power of the river. The other interesting thing to note is the main tributary, the Witteklip River, meets the Storms River at nearly 90 degrees because of the pattern of weak zones in the TMQ.
How gorges are made
A gorge is a narrow valley with steep, rocky walls located between hills or mountains. The term comes from the French word gorge, which means throat or neck. A gorge is often smaller than a canyon, although both words are used to describe deep, narrow valleys with a stream or river running along their bottom. A number of natural forces form gorges. The most common is erosion due to streams or rivers. Streams carve through hard layers of rock, breaking down or eroding it. Sediment from the worn-away rock is then carried downstream. Over time, this erosion will form the steep walls of a gorge. The flooding of streams or rivers increases the speed and intensity of this erosion, creating deeper and wider gorges.>
How the Storms River Gorge was formed
For a very long time, possibly more than 50 million years, the local shore line was at the foot of the Tsitsikamma Mountains, seen on the left hand side of the bridge when looking towards the gorge at ground zero. During this time surf erosion formed a wide, submerged, wave-cut platform. This platform is the flat area stretching from the mountains ending at the coastal cliffs in the Tsitsikamma National Park. From time to time sea levels dropped for a while, exposing the platform to the erosive actions of water flowing from the mountains towards the new coastline.
Whenever sea levels dropped, the natural response of the rejuvenated rivers, in this case what is now known as the Storms River, was to deepen its valley. Valley deepening takes place at a much faster rate than widening of the valley sides hence the deep gorge. The rock in the area is made of very pure quartzite, a metamorphic rock that was once sandstone. The tiny round sand grains in the rock are almost all quartz, a mineral that is strong and combats weathering. The quartzite resists chemical weathering and soil formation, two first steps that would help break down the rocks. As a result, the local rivers runs clear (other than for tannin picked up in the forest), with no sediment to act as sandpaper and further grind away at the quartzite. In this very hard TMQ, the valley sides remain nearly vertical. The Storms River in this case struck it lucky (so to say) that it started to erode a gorge in what was a particularly weak zone in the TMQ. The repeated process of sea level drop and rise helped the river to cut the gorge to their present depth. The process continues at present and the valley deepening is still more prominant than the widening.
The Storms River is also a relatively short river with catchment area that includes the mountains in the back and can, thanks to the high rainfall in the area, flood easily, hence the name. The frequent flooding means that the gorge erosion takes place at a much faster pace than for example in a desert area.
Gorges making history
Since the earliest humans enjoyed the benifits of the wave cut platform and its bounty, the Storms River gorge has formed a major obstacle to human travel in the region. Hunter-gatherers, and later herders, followed animal paths to make their way down and up the precipitous cliffs. The gorge formed a natural barrier that both limited and protected early human endeavours along the coast. Tomas Bain follow the original elephant paths through the gorge as close as possible. The old elephant path is still visible in some places next to the old Storms River Pass. The Storms River gorge was the first gorge on the Garden Route to be bridged in the 1950's, while the others followed in the 1970's. These single-span concrete arch bridges are amongst the highest in Africa. Information obtained from "Garden Route - From Still Bay to Storms River"