Saturday, 20 September 2014

Day 16 - A Wild Volcano Chase

Well the morning started by a wakeup call from a very noisy bird right outside our tent, followed by fighting (very loudly) between two of the big male baboons. One of the males has been outcast from the troop as he challenged the head honcho and lost. So now he is trying to fight his way back in, and apparently failing!

Head honcho is at the back.

Observations I made of the region prior to coming using Google Satellite, revealed two volcanic craters that have been quite impressively affected by EAR faulting. Sleeping Warrior (aka Split Crater) and another that by all accounts has no name. We visited Split Crater back on Day 3, a volcanic cone that has been cut through the middle by a fault resulting in vertical displacement.
As with Sleeping Warrior, the reason to observe the second crater is because the effect of faulting on Menengai caldera cannot be observed as new lavas bury any evidence of fault traces at the surface. Additionally, as previously mentioned, access to the caldera walls to observe any structures, is impossible.

The second crater is about 2km south of Sleeping Warrior. Using the satellite imagery, this crater appeared to have around 100m of horizontal displacement. I wanted to have a look at this because although faults are very rarely clean cut; and by this I mean a fault that is dominated by vertical displacement will have a horizontal element and a fault dominated by horizontal displacement will have a vertical element, I felt it unusual for the fault to be dominated by horizontal displacement in a region that is rifting. All the faults for miles around display vertical displacement as the dominant faulting mechanism, as would be expected.

So, we drove south along the main Nakuru-Nairobi Road to Gilgil, where we needed to turn off. This is where the fun began. We stopped to ask the locals for directions. As on our visit to Sleeping Warrior, many thought we were talking about Olkaria or Longonot to the south, both of which are being/have been developed for geothermal energy. With the assistance of our amazing driver, we managed to get directions, albeit vague ones. Altogether we stopped for directions four times, with two people joining us for the adventure. We still ended up at the wrong crater! This crater was certainly elusive.

The grey linear structure in this image is the location of the fumaroles as seen from the top of the volcano.

Using the satellite images and a good old trusty compass, we managed to approximately locate ourselves as being one crater west of our intended target. A trek among the zebras and a short climb was now required. Finally reaching the top of the crater shoulder and walking around the crater rim, we were satisfied this was our final destination. Over 2 hours drive and 2 hours walking around, we had found it.

As is the case rarely in geology, it was actually a little disappointing. It is a shield volcano, surrounded by predominantly strato-volcanoes, the crater was very shallow, but the reason for the visit, the horizontal displacement was almost negligible! We did however notice fumarole activity close to the base of the volcano along a large fracture that ran almost north-south, again an expected structural trend. 

From the bottom of the volcano, it was possible to get an idea of how flat the rift floor is in places, with the multiple, individual volcanic cones spread across the area. 

This image shows just some of the many small cones that scatter th rift floor in this region

However, this does highlight an important point that I have mentioned a few times now. The importance of fieldwork. As geologists we have access to all sorts of imagery and data sets, and most of the time this is very advantageous. But on occasion, they can have the opposite effect. I could have quite easily made an assumption on the basis of the images, that there was more strike slip faulting in the region than maybe first thought. Of course assumptions are not ideal, but sometimes cannot be avoided. But should I have done that and not made the time to visit the location, subsequent reports could have contained information that is actually irrelevant. 

Tomorrows work will either be a return to a location we want to observe more within the caldera, or work along the top of the north east caldera wall.

Lala Salama from Kenya!

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