Weathering EarthCache
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Weathering alters the texture, colour and composition of exposed materials There are many forms of weathering which can lead to the breakdown of rocks, soil and minerals. Weathering occurs in situ (on site), that is, in the same place, with little or no movement.
Basically, the process of weathering can result to the formation of soil by supplying particles like clay, silt, and sand. In addition, the elements from the weathered rocks supply nutrients for plant and animal consumption.
Natural weathering can be caused by, for instance:
- Temperature changes – heat during the day leads to expansion of rocks and the cold nights causing contractions.
- Water collected in the cracks can freeze and thaw repeatedly, enlarging the cracks over time. - Water entering rock outcrops causes breakdown of the minerals.
- Physical abrasion can be caused by river pebbles and stones rubbing together and smoothing the rough edges.
- Mineral weathering can also be initiated or accelerated by soil microorganisms. Lichens on rocks are thought to increase chemical weathering rates.
- Mechanical weathering: plants can cause mechanical weathering by sprouting and growing in soil that has collected in the cracks of a rock. As the plant grows, the roots extend and spread the crack until the rock eventually break can also be formed by human intervention – see GC6HFPJ
- Biological weathering can be caused by many different plants.
Plants can grow anywhere as long as there is water. Roots of trees or plants in general can biologically weather rocks by growing into the cracks and fractures of rocks and soil. As a result, they become more prone to breakage and eventually fall part. Any plant seed that begins to grow inside a crack or fissure in a rock has the potential to cause mechanical weathering. Even plants with small root structures can eventually crumble a rock. Trees have much larger root systems and can break apart even large rocks and rock structures over time. These seeds may arrive in a variety of ways that range from birds carrying and dropping them to being blown by the wind or traveling via water. A number of plants and animals may create chemical weathering through release of acidic compounds, i.e. the effect of moss growing on roofs is classed as weathering.
The Lebombo Mountains, also called Lubombo Mountains (Portuguese: 'Montes Libombos'), are an 800 km-long (500 mi), narrow range of mountains in Southern Africa. They stretch from Hluhluwe in KwaZulu-Natal in the south to Punda Maria in the Limpopo Province in South Africa in the north. Parts of the mountain range are also found in Mozambique and Swaziland The Lebombo Mountains on the Eastern side of the Kruger Park form a boundary with Mozambique. The name of the mountains is derived from the Zulu word ubombo meaning "big nose". The range is relatively low with heights between 400 m and less than 800 m).
The underlying geology of Kruger Park is predominantly basalt and granite, where the granite is interspersed with gabbro. Shale and sand deposits are fairly minimal and widely dispersed.
Igneous rocks are formed when molten magma, generated deep within the Earth’s crust, rises to shallower levels, crystalising as it cools.
Volcanic rocks erupt, from volcanoes or fissures, at the surface or underwater. They cool and crystalise fast, so are fine-grained. Those that don’t quite make it to the surface, called hypabyssal rocks, crystalise more slowly and are moderately fine-grained, while plutonic rocks, which intrude at deep levels in the crust, cool even more slowly and may be very coarse-grained. The most conspicuous examples of fine-grained intrusive rocks in South Africa are vertical – or nearly vertical.
Landscape development has included the exposure of bedrock surfaces by uplift and erosion, the accumulation of weathered products to form soil s and the subsequent transportation of alluvial sediments within the riparian zone of Kruger’s rivers.
Please email your answers the following questions:
1) You are following the flow of a large river which river is this – the word meaning sand. Which direction is the river flowing?
2) Please comment on the colour of the rocks that you have seen along the banks of the river that you have been following - are they light or dark in colour? Based on what you know about the general geology of the Lebombo Mountains and the KNP in general, what rocks would you say these are and why are they different to the rocks at GZ?
3) When you reach this small ravine, you’ll see a cliff face of pinkish rock.
- a- What is this called?
- b- What causes this colour ?
- 4) Describe in your own words what you see on the cliff face and how it leads to weathering .
Many thanks to Vanessa Strydom - Manager Conservation, Interpretation and Support in the Kruger National Park
GZ is soon to be proclaimed an official geo-site. Details will be added after the KNP has published the book.
Additional Hints
(Decrypt)
Erzrzore gb fhozvg lbhe nafjref