Saturday, 13 September 2014

Day 9 - It's a Fissure for Sure

Today was the second day of mapping. It was a scorcher this morning, with dust devils and races against the thunderstorms in the afternoon. 

Working Road Side Can Be Dusty Business

As I have previously mentioned, the caldera is huge and due to access, mapping is to a certain extent controlled by just that. The area is too big to map in the time I have, but a start is being made by using the roads as a guide, stopping whenever something potentially interesting is observed and heading off to explore. The structure of today was to concentrate on the central to southern part of the crater. The first task was to sample ropey lavas that we observed on day seven. Large ropes have been observed in several locations around the caldera, just peering through the vegetation. I am curious to see if they are one and the same, covering a very large area.

Ropey Lava

After sampling from the first site, we walked a few hundred meters to the south west around the fumarole lavas from day 7, to collect another sample and make observations. It was quickly established that the ropes on this side of the fumarole related lavas. We also established that the ropey lava flows on the north east side are likely to be the same as the flows observed on the south west side. However, on the south west side, there are two more, younger ropey flows. Further investigations of these flows revealed several fairly large fissures cutting through all three flows. The dominant fissure has a NE-SW trend with the other three rotating through to ESE-WNW, but amalgamating with the dominant fissure. These fissures run perpendicular with those observed on day 7. 

Due to the dense vegetation in the vicinity, it is difficult to say if it is one large fissure that curves, or several that are perpendicular to each other. These observations leave no doubt in my mind that these are the fissures responsible for the recent fissure eruptions mentioned by Mariita (2013).

The afternoon was in part spent trying to find evidence for ropey lavas in other locations to the south. Though we found some evidence, it was not convincing, so no more samples were collected today. Instead we investigated the often enormous and numerous blocks to the east and south east of the caldera. Many of the blocks contained volcanic lithologies similar to a’a and pahoehoe lava flow as well as tuff deposits. We concluded these huge blocks are likely to be mega breccia associated with one of the piecemeal stages of collapse.

Further along the road, there was evidence of tuff deposits burying volcanic bombs, though we did not realise they were bombs until we removed a piece. on the outside it was as white as the clay we had observed yesterday. There was also evidence of scoria bombs with in the tuff.

Bottom centre of this image is where we discovered a bomb

Inside the bomb

Tomorrow will be more of the same, with the aim of starting in the middle of the caldera again, heading west this time. Lets see what else we can find!

Lala Salama from Kenya!

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