Searching for WW I German armaments in Namibia, 2017So I have had a few unusual survey proposals over the years, Yagan’s head comes to mind for example, but a call back in October led to a trip at the end of the year to Namibia. At first I thought the request a little bizarre and one in which I would be of limited help but on talking the problem through I saw that perhaps geophysics might be able to add to the investigation.
So what was the request? Well it started with a story surrounding the retreat of German troops from Namibia during WW I. The story goes that as the German Schutztruppe ("protection force") left the country they disposed of various armaments in the sinkholes around the town of Tsumeb. In particular the lakes of Ojikoto and Guinas were suspected to contain field guns, rifles, carriages, ordnance and even (as always in these cases) a safe full of gold!
|German WW I field gun in Ojikoto Museum|
This was too much to resist!!
The architecture of the caves and even their depths were in dispute despite a long history of local divers testing their prowess at exploration. Descriptions by local divers Chris Steenkamp and Johan le Roux (who provided incredible support throughout the trip - thanks guys) talked of overhanging caves extending unknown distances with jagged roofs and a very soft sediment on the lake floors. The region is one of limestone and dolomite with a regional fracture pattern that shows linear trends to the lakes. Along the weakened trend the lakes open up as sink holes and thus have steep to vertical sides. These were going to necessitate some unusual access means and a very portable geophysical survey platform.
The steep sides of Lake Guinas Lake meant that we had to abseil the inflatable boat into the sinkhole before setting up the equipment. However, once on the lake the sonar produced fantastic maps of the underground structure showing the bell-like form of the sinkholes and also providing a series of targets for the dive operations.
In Lake Ojikoto these were at 30-40m depth and proved to be a carriage gun and boxes of shells however in Lake Guinas the depth of over 100m was way beyond my comfort dive range and so remains to be investigated with remotely operated vehicles (ROVs) and cameras.
The sonar produced a really great map of the underside or roof of the sinkholes even where the angle was very small compared to the water surface but the data set did require some significant manual filtering as the geometries of the structure was anything but typical for sonar data. Still, it just goes to prove that often you really do not know what you will get with geophysics until you try!
|"outer" walls of cave|
|point cloud view of cave walls|
The “expedition” was in part sponsored by a US Travel channel so watch out for Josh Gates and Expedition Unknown to be broadcast on March 6th in the US on the Travel Channel.
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Unfortunately, no gold yet but we will continue our hunt for the means to support the Schools future………
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