Day 9 - Sunshine and Thunderstorms

As soon as the sun came up this morning you could feel the heat. It was a very warm day today, and as someone who is most at home high in the mountains or in the Arctic I could feel myself struggling a bit in the heat. In part this was down to foolishly not drinking enough water as I perked up a lot when I got some water in me. But I think I have met my match working in the kind of heat we had today. Don’t get me wrong, I’m not complaining. I’m loving the sunshine, the heat and the tan, and I could certainly get used to this :)

After getting some water in me I was back to my usual self, climbing on anything I can.

Today we were mapping in the southern section of the caldera, though we began by going back to where we found the fissure and fumaroles on day 7 to collect a sample of the ropey, Pahoehoe lava that the fissure erupted into.

A lovely example of a ropey 'pahoehoe' style lava flow.

Right beside the fissure we found another set of fissures orientated perpendicular to the first set. Once we put these on the map and collected a sample of the ropey lava we drove round to the south and began mapping.

The mapping we are doing here is quite different, and less detailed from what I was doing at the beginning of the summer -my mapping project for uni- in Skye. On my return from Kenya I will be doing a lot of work on my mapping project and will be blogging all about geological mapping and my time on Skye. So I will only give a brief overview of what mapping entails just now. Essentially when mapping you identify the rock type, making notes on it and collecting any measurements you can. You then locate yourself on a basemap which you will have produced beforehand – this will have the topography (contours) on it along with gridlines and any other information, such as roads etc., that will help in locating yourself.

An example of mapping in progress... the basemap on which I have put the different rock types where I saw them. From Skye mapping June 2014.

Locating yourself requires good navigation skills, which is wonderful for me as it ensures I am practising the navigation skills I need for working toward my mountain leader qualifications. Once you have located yourself on the map you then draw on the exposure of rock you have identified and colour it in – as you get more rock types you use a different colour for each. One of the most important things to do when mapping is to locate and trace the boundaries between different rock types. In some cases this is very easy as, if you are lucky, the boundary can easily be seen at the surface. More often than not however, boundaries have to be worked out based on the information you can collect from the rocks.

For the fieldwork here in Kenya we are quite fortunate as the landsat images we have show the different lava flows. So we already have a very good idea of where the boundaries are. We are simply ground-truthing these by going to certain locations and making sure that what the landsat image shows us is what we observe, and then identifying (or at least attempting to) the type of lava - in some cases we have found it not to be a lava, hence the need for ground truthing. This method makes mapping a fair bit simpler for us, however we need that as the area we need to map is huge! Working mostly at the roadside does have its drawbacks though….

A dust storm from a passing lorry heading towards us. We were covered in dust by the end of the day.

…as it is very dusty, especially when the lorries drive by.

We had a very productive day today, managing to complete all that we needed to within the southern section of the caldera. Our day finished with a bang as a thunderstorm rolled in. The drop in temperature was welcomed by me. It didn’t last long though as I write this looking out at the sun setting over the caldera! Life’s pretty sweet living on the edge of the worlds 2nd largest caldera.

I realise I’ve been posting for over a week now and at the beginning I promised to explain what a caldera is… A caldera is an ancient volcano which has collapsed in on itself. This collapse is usually caused by a drop in pressure in the magma chamber, likely due to the emptying (or partial emptying) of the magma chamber. The result is a very large crater-like feature. Here at Menegai the caldera covers an area of about 80km2.

A cartoon showing the steps of caldera formation, using Mount Mazama as an example.

The collapse can occur in one instant, or in a series of collapses. We believe from what we have observed so far that the Menengai caldera collapsed in multiple phases. Associated with the collapse event(s) are large pyroclastic eruptions. These are highly explosive, with very hot and very fast flows which destroy everything in their path.

In many cases, Menengai being one of them, volcanism doesn’t end with the caldera collapse. There can be extensive subsequent eruptions and lava flows within a caldera. We have already mapped multiple lava flows, fissure eruptions and a couple of scoria cones within the Menengai caldera. All of which have occurred since the caldera collapse. The sun has now set, and we have a beautiful, clear starry sky to stare up at, accompanied by music from the crickets – a very soothing sound that I think I’ll miss once back home. I feel like I’m in the scene from the Lion King when Mufasa and Simba are stargazing. If I had brought my sleeping bag, or it wasn’t so cold I would probably bivi out (sleeping under the stars with just your sleeping bag) as it is such a beautiful night. It gets very cold here once the sun goes down, even by Scottish standards! I quite like it if I’m honest, and it certainly makes me appreciate the hot water bottle waiting for me each night :) jitunze (take care)