Monday, 22 September 2014

Day 18 - Always Expect the Unexpected

Today we returned to the northern part of the caldera to investigate a deep gulley running almost NE-SW along the caldera wall. According to the contours on the site map, the gulley dropped from an elevation of just over 1800m to just over 1300m and back up again, over a distance of about 200m. First observations of this structure were made from the road on Day 13. From this vantage point the gulley looked like it may have formed during the caldera collapse, where in this area, the core of the volcano detached from the caldera wall during this collpase phase. Both the caldera wall and the opposing wall appear to be steep. The position of the gulley matches that of inferred NE-SW striking faults of Mariita (2013). It also meant we may have another opportunity to observe the caldera walls and potentially collect structural data. The nose of the NW crater flow is also at this location. 

The distance to the caldera wall looks much further than it actually was. Jenny was route decider today!

The nearest road was about 800m east of our intended destination. Walking in the approximatly west, the topography had a gentle slope down towards the northwest, with three sudden drop offs every 150m or so. These steep drops were the nose ends of three separate ropey flows we had previously observed in multiple locations across the caldera. They were also easy to climb down with rubbly flow ends forming natural deep steps.

One of the clambers down the lava flows 

Almost arriving at the southern side of the NW crater lava flow, we met a farmer, who was a little wary of us. Once our driver had spoken to him about what we were doing he relaxed a little.

On arriving at the location we discovered that the gulley was not quite what we were expecting. Instead of our exciting inference, admittedly made from a distance, the gulley only had vertical walls on the side of the caldera wall. The opposite side of the gulley is made up of nose ends of ropey lava flow lobes, the flow being about 10m think. Sadly there were no structures to measure.

Jenny and I discussed the course of action regarding getting up to the caldera walls. Along large lengths of the caldera wall, there have been landslips, all of which were potentially blocking our route up to the caldera wall. We decided to walk down the sloping topography following the south edge of the lavas from the NW crater and assess the stability of the landslips when we were at their bases. We were just about to leave, when the farmer said something to Vincent our driver in Swahili. Vincent quickly advised us not to go any further as the thick vegetation at the base of the slope is the day time resting place for three leopards.

The above image shows the debris along the caldera wall that has accumulated during recent small scale landslips. The rich green vegetation is leopard home!

From as close as we were aloud to get (our driver worries!) we could see vertical fractures in the caldera wall that had a strike of almost E-W. Again it is this trend of structures that appears to dominate. It was very clear to see at this location, that the collapse phases that occurred directly next to the caldera wall all occurred vertically. 

Our day ended earlier than planned today. Sometimes it can't be helped.

Lala Salama from Kenya!

No comments:

Post a Comment