Your tasks – the C.S.I. work!
At GZ you will find a couple of huge granite boulders. You are allowed to alight from your vehicle here but remember that you are in the Kruger park and that wild animals do roam freely here. YOU HAVE BEEN WARNED AND DO SO AT YOUR OWN RISK!
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 you understand by the term “erosion” and what type of erosion has caused these huge boulders to be as they are today?
2 – Look at the colour and striations that you see and comment on the colour of the striations. How many different coloured VERTICAL striations do you see and what do you think caused them?
3 – What do you think the HORIZONTAL striation band is and why do you think your answer is correct? How wide is it?
4 – Describe any other interesting things you saw or experiences you had on your journey to the site from the main road – Photos are always welcomed in the logs but please don’t post photos of the boulders themselves.
5 – At GZ there is a sign – what does it say? What happened to Stevenson-Hamilton at this place?
6 – OPTIONAL – post a photo of your team at GZ.
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.
What are Igneous Rocks?
Igneous rock (derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust.
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What is Granite?
Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. The term 'granite' also applies to a group of intrusive igneous rocks with similar textures and slight variations on composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking matrix of feldspar and quartz. Occasionally some individual crystals are larger than the groundmass and can easily be observed.
[Have a careful look at the boulders at GZ and see if how many different colours of crystals you can identify – for interest and not a question that needs to be answered.]
Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume. Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. Granitoid is a general, descriptive field term for lighter-coloured, coarse-grained igneous rocks.
Some different coloured granite
Weathering
Weathering is the alteration and breakdown of rock minerals and rock masses when they are exposed to the atmosphere. Weathering processes occur in situ, that is, in the same place, with no major movement of rock materials involved. Weathering is a fundamental Earth process.
Weathering Processes
Two main groups of weathering processes are identified, with a third supporting group:
Physical weathering: the group of processes, such as frost wedging and volume changes of minerals, that result in the mechanical disruption of rocks (e.g. granular disintegration, exfoliation, joint block separation, shattering by changes in temperature or pressure). Mechanical processes dominate in cold and dry climates.
Chemical weathering: the decay of rock forming minerals caused by water, temperature, oxygen, hydrogen and mild acids (e.g. solution, hydration, oxidation, carbonation). Processes of mineral decay dominate in warm and humid climates.
Biological weathering: the group of processes that are caused by, or assisted by, the presence of vegetation, or to a lesser extent animals, including root wedging and the production of organic acids. Vegetation, and animals, tend to be more active in warm and humid climates.
Rock Type determines the resistance of the rock to the weathering processes that operate in that particular environment. Each rock type is composed of a particular set of minerals, which are joined together by crystallisation, chemical bonding or cementing. When the forces of plate tectonics move these rocks from the environment in which they formed and expose them to the atmosphere they begin to weather. Highly jointed or faulted rocks present many planes of weakness along which weathering agents (e.g. water) can penetrate into the rock mass. Erosion: the dynamism and efficiency of erosion determines how rapidly any weathered material is removed, how frequently fresh rock is exposed to weathering, and if deeply weathered profiles are preserved.
A Little Bit of History
James Stevenson-Hamilton (October 2 1867 - December 10 1957) born in Scotland was the eldest of nine children. He married Hilda Cholmondeley, who was 34 years his junior. She bore him three children.
On 1 July 1902, he got himself appointed Warden of the Sabi Game Reserve.
Stevenson-Hamilton was not sure of what was expected of him and when he enquired as much from his superior he was famously told to 'go down there and make yourself thoroughly disagreeable to everyone!' For the first few months Stevenson-Hamilton stayed at Crocodile Bridge. Then he moved to Sabie Bridge where he had his headquarters. He thoroughly explored his domain and appointed the first game wardens, black and white. That Stevenson-Hamilton took his job seriously was emphasised when he had two police officers, who had poached game, arrested and convicted. This incident earned him quite a reputation.
In 1903, he managed to stop the movement of cattle through the park. He also managed to stop all prospecting for coal and minerals. With the proclamation of the Singwidzi Game Reserve in May 1903, Stevenson-Hamilton took over the management there as well.
In 1914, the First World War started and Stevenson-Hamilton joined the forces in the north. He left the administration of the reserves to Ranger Cecil Richard de Laporte and after that to Major A A Fraser. Upon his return in 1920, he found everything in a shambles. Fraser had let the administration slip into a mess. Further concerns surrounded the fact that the war had stimulated development and greedy eyes looked at the reserves for agricultural ground.
Stevenson-Hamilton fought on every front to save the reserves. Instrumental in helping him was the establishment of the Selati Railway Line, which was originally built to transport gold. However, the gold reserves soon began to dwindle and in 1922, in an attempt to increase the profit of the railroads, the Round in Nine Tour was established. This was a 9-day tour of Mozambique and the Lowveld and included a one-night stop at what is present day Skukuza, and the idea of allowing people into the reserve was born.
Stevenson-Hamilton got members of the Provincial Council to visit the reserve on one of these tours and they left with a better understanding of the possibilities of a national park.
He was known as Skukuza, a Shangaan name meaning either ‘he who sweeps clean' or 'he who turns everything upside down', by his staff at Kruger National Park. In 1936, the main rest camp's name was changed from Sabie Bridge to Skukuza to honour him. Stevenson-Hamilton remained with the park until his retirement on the eve of his 80th birthday in 1945.
In 1927, the Park was opened to the public who where charged a £1 fee. Only a handful of cars visited the new Park that year, but in 1935, some 26,000 people passed through the gates. Today the number is around one million per year.
REFERENCES:
http://geologycafe.com/erosion/weathering.html
https://en.wikipedia.org/wiki/Granite
http://geology.com/rocks/granite.shtml
