Part 3 A Gorge-ous site for dates thanks to a very old river

Before Victoria Falls formed, the Zambezi River was very much like we see it today above the falls – wide and shallow.  But the old Zambezi was not where the Zambezi flows today. It has left remnants of its former presence 12-15m above the modern river in the National Park, and the gravels it left there also contain artefacts.  If they can be dated then we will have a maximum age for the cutting of the falls (why the falls formed is a contentious issue among geographers).

Zambia has none of the volcanic debris that facilitates dating of the archaeologically famous sites in East Africa such as Olduvai Gorge, so the potential to date the exposure of gravel to sunlight using optically stimulated luminescence (see last post for idiot’s guide to OSL) is a real bonus to the project. The technique  has been invaluable in places like Zambia where there are few other reliable options.

We dug a small pit for Geoff and even though the gravels were shallow (30cm) he was willing to try his magic on these.

ZG17 handaxe

One of the many handaxes among other Early Stone Age artefacts in the gravels of the old Zambezi (with Ken and Maggie)

The scouts who accompanied us could not believe the story of a once higher Zambezi.  Wry smiles and shaking heads accompanied our explanations.

There are also gravels left high and dry downstream of the modern falls on a series of flat top platforms that mark the position of previous falls.  They form a six mile long zig-zag leading to the present falls. The contrast couldn’t be greater between the tranquil Zambezi above the falls and roiling torrent below. The earliest and furthest from the falls is at the confluence with the Songwe River where there is a spectacular gorge.

Songwe Ken Mbewe

Ken (right) and Richard Mbewe (middle: Senior Archaeologist, National Heritage Conservation Commission) watching white water rafters in the far distance with a member of a raft recovery crew

It’s a beauty spot, but also a National Monument for its abundant Stone Age remains. The gravels contain raw materials, such as glass-like chalcedony, that are perfect for making stone tools.  It’s a rare resource in an otherwise barren landscape for tool-makers.

Songwe gravel surface find MSA

Beautiful chalcedony flake, Middle Stone Age, from the surface of the Songwe gravels and showing some of the natural varnish that forms on artefacts and cobbles along the Zambezi

We took Geoff there because of the gravels and a patch of sand that might be sitting on the gravels.  Early in the season we had visited Songwe and found pits in the sand-cover where it was being collected as building material.  A quick scrape with a trowel in these pits revealed Middle Stone Age (MSA) artefacts.  Not the big stuff we found at Maramba, or on the sand scarp, but still part of the record of humans in this landscape and worth dating.

We spent an hour or so tracing the Songwe gravels and noting how thin the spread is and wondering how it might be dated using OSL.  Bedrock was just beneath the surface – no chance here for Geoff’s technique.

Songwe Gorge and gravels

Geoff standing on the surface of the Songwe gravels and looking up the Songwe Gorge

Next season we’ll have Andy Hein (University of Edinburgh) with us who specialises in dating how long surfaces have been exposed to the sun, just the opposite of Geoff’s magic.  We gave up on the gravels and returned to the sand pit and its known MSA.  After clearing the surface of the pit floor a 1m square was laid out and excavation began.  It wasn’t long before very sharp flakes started appearing, some smaller than the nail of your little toe – a sign we were in a relatively undisturbed deposit where even the smallest manufacturing debris remained.  That’s rare and this place is on the growing ‘to do’ list for next year.

Songwe Sajds 1 closeup of knapping debris

A very sharp little toe-nail size chalcedony flake from the MSA sand overlying the gravels.  Pieces this small hint that evidence for artefact manufacturing will probably be well preserved

Songwe Sands gravels (2)

The Songwe gravels at the base of the pit.  We managed to excavate about 15 cm before the light faded.  How deep do they go?  We’ll find out next year


Another time, this might be productive

But there was another surprise in store – the gravels of the Zambezi.  They formed the bottom of our square and there was no doubting these were river gravels given the rounding of the stones.  There were also artefacts in the gravels, probably Early Stone Age based on size, also rolled from river action.  Whatever they turn out to be in terms of archaeological labels, they are very different from the fresh material on top.  Out came the thick black plastic and Geoff was buried again.  He collected samples from the overlying sands and two cobbles from the gravels.

Songwe Sands1 dosimetry

Geoff collecting the background radiation levels from one of the three samples taken.  He also collected cobbles from the Songwe Gravels for dating

We were rapidly running out of daylight and still there was gravel to be excavated.  It will have to wait until next year.  And maybe a year from now we’ll have some OSL dates to share with you.

And so, field work all but at an end, what more is there to say?

Well, just few practical matters still to sort out …


One thought on “Part 3 A Gorge-ous site for dates thanks to a very old river

  1. Will you be posting results of work on samples? Next year’s field season is an awful long time away. Has your work at Kalambo Falls been published? Any advance on Bangweulu? That’s fascinating.


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About Larry Barham

My name is Larry (Lawrence if I’m feeling formal) Barham and I'm a Professor of African Archaeology at the University of Liverpool, England, teaching evolutionary anthropology at undergraduate and postgraduate level.