I am just about to leave for Tanzania to do some offshore
archaeological surveying with Ted Pollard from BIEA (I will be blogging on this
on my return) but I thought before I went I would post a short video that was
compiled during a field campaign late last year to the Rift Valley in southern
Ethiopia.
I made this trip together with Dei
Huws (Bangor Uni) and Tigistu
Haile (Addis Ababa Uni) as part of a much larger, international project
that is drilling a number of locations throughout East Africa that are linked
to key Hominid sites. The overall aim of
this is to be able to provide dated information about environment and climate at
key stages of hominin development and
migration.
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The Chew Bahir site is located in SW Ethiopia close to the
boarder with Kenya. The large valley generally
drains to the south into Lake Stephanie but the northern part where we hope to
drill our core is only flooded on an infrequent basis. As with many of arid areas, when it rains it does
so often causing drastic and violent floods from the surrounding uplands that
wash coarse river gravels far out into the generally flat valley floor. Since our drilling objective is to obtain as
simple a geologic sequence as possible the first task is to locate an appropriate
site that has not been affected by the alluvial fans on the valley side or any
of the ancestral rivers that migrate across the valley bottom.
So, in November we made a preliminary field visit to the
site armed with magnetic and electrical resistivity tomography/imaging (ERT)
equipment in order to find appropriate sites.
Our choice of locations for the geophysics was based on some regional
background work on geophysical signatures and also on some local knowledge kindly
shared by Tullow Oil Plc.
The site is quite special and like nowhere I have worked
before as you can see from the video. We
managed a couple of sites during our survey, one in the centre of the basin,
the preferred core location, and one over an alluvial fan sequence at the edge
of the basin. The ERT gave some great
results despite the arid conditions mainly I think because of the relatively
high conductivity of the lake sediments – likely a result of the periodic
wetting and drying. The alluvial fan was readily recognised in the ERT sections
at the basin edge but no signatures of this were recorded at the centre of the
basin where a fairly uniform sequence was modelled.
The next stage from us it to return to do a seismic
reflection survey in order to image the top 400m (the core depth) in much
greater detail.
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