This cache is part of the Chappies Walking Series. Enjoy the beautiful scenery which is often missed when in the car.
This spectacular roadway took seven years to complete, at a cost of ₤20 000. The Hout Bay - NoordeHoek Road ‘hewn out of the stone face of Sheer Mountain’ was opened to traffic on Saturday 6 May 1922 by the Governor of the Union of South Africa, His Royal Highness Prince Arthur of Connaught.
You can park in the bottom and work your way up from there. This road is normally quite busy with cyclists, joggers, walkers and cars so please be careful on the road. Please also be vigilant when looking for and logging the caches.
Sandstone or Granite:
Please help me to find out if this is Sandstone or Igneous rock.
Sandstone is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow, red, gray, pink, white and black.
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava.
You can make use of the following links to research:
http://en.wikipedia.org/wiki/Sandstone
http://en.wikipedia.org/wiki/Igneous_rock
http://blogs.agu.org/georneys/2011/06/14/chapmans-peak-nonconformity
http://www.capetourism.co.za/cape-town-info/general-info/geology.html
http://web.uct.ac.za/depts/geolsci/cape.htm
Erosion:
Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations.
While erosion is a natural process, human activities have dramatically increased (by 10-40 times) the rate at which erosion is occurring globally.
Excessive erosion causes problems such as desertification, decreases in agricultural productivity due to land degradation,
sedimentation of waterways, and ecological collapse due to loss of the nutrient rich upper soil layers. Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage, making excessive erosion one of the most significant global
environmental problems we face today.
There are a few types of erosion:
1) Water Erosion:
There are three primary types of erosion that occur as a direct result of rainfall—sheet erosion, rill erosion, and gully erosion. Sheet erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by rill erosion, and finally gully erosion (the most severe of the three).
The impact of a falling raindrop creates a small crater in the soil, ejecting soil particles. The distance these soil particles travel (on level ground) can be as much as 2 feet vertically, and 5 feet horizontally. Once the rate of rain fall is faster than the rate of infiltration into the soil, surface runoffs occurs and carries the loosened soil particles down slope.
Sheet erosion is the transport of loosened soil particles by surface runoff that is flowing downhill in thin sheets
Rill erosion refers to the development of small, ephemeral concentrated flow paths, which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically on the order of a few centimeters or less and slopes may be quite steep. This means that rills exhibit very different hydraulic physics than water flowing through the deeper, wider channels of streams and rivers.
Gully erosion occurs when runoff water accumulates, and then rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.
2) Wind Erosion:
Wind erosion is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as deforestation, urbanization, and agriculture.
Wind erosion is of two primary varieties: deflation, where the wind picks up and carries loose soil particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) surface creep, where larger, heavier particles slide or roll along the ground; (2) saltation, where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) suspension, where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50-70%) of wind erosion, followed by suspension (30-40%), and then surface creep (5-25%).
Wind erosion is much more severe in arid areas, and during times of drought. For example, in the Great Plains, it is estimated that wind erosion soil loss can be as much as 6100 times greater in drought years, than in wet years.
3) Gravitational erosion:
Mass movement is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of gravity.
Mass movement is an important part of the erosional process, and is often the first stage in the breakdown and transport of weathered materials in mountainous areas. It moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope.
Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression, in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence.
Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm in diameter by wind along the soil surface.
4) Exfoliation:
Exfoliation is a type of erosion that occurs when a rock is rapidly heated up by the sun. This results in the expansion of the rock. When the temperature decreases again, the rock contracts, causing pieces of the rock to break off. Exfoliation occurs mainly in deserts due to the high temperatures during the day and cold temperatures at night.
References: Wikipedia http://en.wikipedia.org/wiki/Erosion
Questions for the Earth Cache (please email me your answers):
1) Please take an optional photo of you with your GPS at the cache site.
2) Please explain what you think caused the erosion on these rocks.
3) What is this sort of erosion called?
4) What is the color of the rocks in this area?
5) What sort of rocks do you think these are? Sandstone or Granite?
6) Do you think that there is anything more that can be done to prevent further erosion in this area?