Great Rift Valley Eastern Escarpment EarthCache
Great Rift Valley Eastern Escarpment
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The co-ordinates take you to an information board located at a viewpoint on the Eastern Escarpment of the Great Rift Valley, where there is a layby. Please take care to pull off the road completely and park safely here, as the main B3 road is a very busy route.
From this viewpoint you have a good view of the Great Rift Valley spread out before you. In order to log this cache you need to answer the questions at the end of the main description.
This valley is part of the East African Rift system, which has two main branches, the Gregory Rift and the Albertine Rift. This active continental rift zone is a developing divergent tectonic plate boundary, as the Africa plate splits into two new tectonic plates which are slowly drifting away from each other. Given the right conditions, the valley below you may eventually – many millennia in the future - become an ocean A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. This takes the form of crustal extension, a spreading apart of the surface, which is subsequently further deepened by the forces of erosion. When the tensional forces are strong enough to cause the plate to split apart, a centre block will drop down relative to its flanking blocks, forming the graben which you can see in the valley before you. This action creates the nearly parallel steeply dipping walls, typified by the steep escarpment you are standing on. As this rifting process continues, the valley widens, until it becomes a large basin, which fills with sediment from the rift walls and the surrounding area. Where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake, such as nearby Lake Naivasha. The axis of a rift area may contain volcanic rocks, and active volcanism is a part of many active rift systems. Mt Longonot (2,776m), a dormant volcano which last erupted in 1900, lies around 20 km northwest from the cache co-ordinates and should be visible in good atmospheric conditions. Due to local variations in the rifting process and erosion effects, the width and depth of a rift valley may vary along its length. Looking east from the cache location, the valley floor is around 1,650 metres above sea level (ASL). Yet a few miles further south the valley floor drops to just over 1,000 metres ASL. From the 1,650m contour due east from the cache location the land slopes gently upwards over 4 kilometres until it reaches the foot of the escarpment proper at 1,800 metres, an average gradient of around 2%. From this point the slope gradient changes dramatically and climbs rapidly to reach the viewpoint in less than a kilometre. If you drive on the B3 road traversing the escarpment side, you will appreciate why the road gradient sometimes requires a braking tractor to be attached to a heavy goods vehicle to facilitate a safe descent!
To log this cache, find the answers to the following questions and email them to us via our profile on Geocaching.com:
1. What are the names of the two new tectonic plates which are the result of the Africa plate rift splitting?
2. What forces influence the depth and width of a rift valley at a given point?
3. Measure the height of the viewpoint above sea level. Give your answer in metres.
4. Assuming that the horizontal distance from the 1,800 metre contour line at the foot of the escarpment to the viewpoint is 1 kilometre, what is the average gradient of the slope from the foot of the escarpment to the viewpoint. Give your answer to the nearest degree.
You may log your find immediately; we will contact you if anything is wrong. However, please do not include any answers in your log and do not post any photos of the information board.
Congratulations to CyclingBadger for being First to Find!
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