Day 5 - The Caves...a puzzle to be solved

Learning yesterday that the caldera walls are essentially inaccessible we decided to try a new approach. We will look for faults and fractures on the outer edges of the caldera. We decided to start today by heading to the highest point on the edge of the caldera – the viewpoint looking out across the entire caldera. From here we could play a game of geology i-spy... picking out features from above.

Top - The viewpoint as seen from our accommodation. Bottom - panoramic of the caldera looking down from the viewpoint.

We have quickly learnt as well that you can’t go anywhere for free here. As the viewpoint is a tourist attraction there were entry fees, and they insisted on us hiring a guide. The extra expense was at first, a bit annoying especially as we were there to work more than anything else. However our minds were quickly changed. Our guide, Daniel, was fantastic. He was very keen to learn about the geology and our fieldwork, and also told us about lots of features nearby that he was unsure how they formed. These features were some of the faults we have been looking for, and we would not have found them ourselves! Thank-you Dan :) Dan also told us about some caves and offered to show us to them. There were three in total, all very close to each other. Of all of them we could only be sure how one of them formed. The other two have us somewhat perplexed...

Looking into the first 'cave' from the top. Possibly an old flank vent, that has been exposed by the caldera collapse, though we are not confident of this interpretation.

The first cave we visited was on one of the less steep walls of the caldera. It wasn’t really a cave, as it was open. We did, however, have to crawl through a small tunnel to get into it. Although the scrambling didn’t bother me last night’s spider incident did. Daniel assured me that there were no spiders. I wasn’t convinced but I also wasn’t going to miss out on getting into the crater. So I made my way quickly through the tunnel only to see this once inside….

No spiders! not so sure of that myself....

Having seen all the webs, it was a nerve-wracking scramble back out!

Refusing to let spiders get the better of me, we began to study the crater – though whether it is a crater or not is questionable. Even more at question is IF it is a crater, was it formed before or after the caldera collapsed? At first we thought the entrance tunnel (what I'm climbing through in the picture above) was a fault, and we took measurements, and even found faint slickenlines - scratches in the fault surface caused by the rocks moving past each other. Though by the end Helen wasn’t convinced it was a fault and thinks might actually be a lava tube. I’m still unsure, I think it was a fault (that maybe was exploited by lava, to become a lava tube) though it appears to abruptly end within the crater. Also puzzling were the rock types, in particular the order of them in relation to our initial understanding of the caldera collapse and subsequent eruptions. There were large deposits of tuff (pyroclastic flow deposits) with lava both above and below. Which doesn’t fit with our understanding of the Menengai area as a whole, or the best interpretation of the crater feature. We do see tuff all over the caldera, as caldera collapse is accompanied by pyroclastic flows. But to see it here, surrounded by the lava’s asks more questions than it answers. Though that is often the case in geology (and science as a whole).

The crater in which the second cave was in. A holy place to many locals due to it's beauty (inside).

The second cave was in what is most definitely a crater on the flanks of the (now dormant) volcano. The crater was beautiful, and understandably a holy place to many locals. In one of the crater sides is a large cavern which opens up to be about 30m wide and 10m high.

Standing in the entrance to the cavern.

There was evidence of lava flow in the lower 2.5 m of the cavern walls, but we could not see any evidence of lava flow above this – granted the torch light wasn’t so great looking from a distance. When lava has flowed through you tend to find a blobby texture to the walls, and ceiling caused by droplets of lava. Had there been clear evidence of lava flow on the ceiling of the cave you could happily call this a failed lava tube; failed, because it didn’t lead anywhere. Helen’s thinking is that, the crater had a lava lake and that this cavern was created by overspill and fluctuating levels of lava within the lake. I like this idea and think it is a good theory as to the formation of the cavern.

As we were leaving the cave, we noticed 'dropstones' in the crater walls. You could see that volcanic bombs (chunks of rock thrown from a volcano in an eruption) had landed in cooling lava. In some places deforming the lava .

Can you spot the 'dropstones' in the crater walls?

The third and final cave we couldn’t enter because of bats; they can be carriers of ebola – though no worries of ebola here in Kenya!

Looking into the third cave. You can see the 'bobbly' texture which indicated this was a lava tube. This is the only known enterance to the cave, and only exists as the ceiling of the cave collapsed at this location.

Just looking into it we could confidently say that this was a lave tube. Daniel told us that he has never made it to the end of this cave (lava tube), it is very long and he thinks it may lead right through into the caldera. I would love to come back when the bats are not in the cave and venture along it. Daniel was a fantastic guide, and he really appreciated us sharing with him our knowledge and understanding of the geology of Menegai. So much so that he asked for us to help with the production of a tourist guidebook to the Menengai caldera. Of course we said we would be happy to help where we can. He also told us that Menengai is a Masai word meaning mass-death. The caldera is called this as many Masai were killed in the eruptions of it. So much of what we saw today produced many more questions than it answered. I would love to be able to come back here with more time to be able to study the rocks and how they relate to each other in more detail. If possible I will come back to collect measurements and samples to hopefully answer some of the questions I have uncovered today. It is still very much a puzzle to be solved. Maybe we can make a trip back here before we leave, if not I’ll just have to come back to Kenya some time ;)