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Notes on the Koobi Fora Spit Site
The site at Koobi Fora Spit (GaJi12) was discovered by the Koobi Fora Field School in 1987. It was used for leveling, mapping and survey exercises on and off over the next nine years. It records low-water cultural facies over about the last eight millennia and a sequence of harpoons that suggests the systematic development of this technology throughout this period, right into the Iron Age. Finally, it demonstrates that more attention should be given to low-elevation archaeology along the shore of Lake Turkana as it continues to retreat.
Situation & Structure
Koobi Fora Spit seen from the west. GaJi12 lies on the south (right) side of the spit opposite the bandas of the field station. This photograph was taken prior to 1985 when the lake was still fairly high. As can be seen here, the prevailing wind comes from the south, helping to drive the long shore current that moves sand westward along the southern margin of the spit. This causes the spit to grow to the west, a process that is accelerated by the falling lake level.
Looking eastward along the southern shore of Koobi Fora Spit near its terminus. Note the scalloped shore, the various degrees of stabilization between the shore and the cut bank, and the band of sand that has accumulated at the base of the cut bank.
If you look at the top photo on this page, you will see some black-looing pools behind long shore sand bars on the south side of the spit. This photograph, taken in 1987, shows such a long shore bar and the pond that had developed behind it. This generally occurs when there is a small seasonal rise in the lake corresponding with the rains in Ethiopia. As the lake level drops along with these small seasonal transgressions there is both erosion and deposition along the shore.
The long shore westerly current and wind-driven waves from the south combine in the mouth of a small lagoon to create these scollop-shaped ripples in a few centimeters of water. The light areas are crests of light-colored sand; the darker areas are black sand covering a muddy bottom. These features are often covered with a thin layer of sand by wave action as the lake retreats.
When left high and dry, the sand is sometimes blown off these scolloped surfaces leaving a flotsam of small objects thrown up in the surf. In this case, there is a microlith (upper left), two flakes of agate (one weathered to a white color) and a small fragment of vein quartz, in addition to a scrap of bone and some sandstone fragments. The gray patches in the black sand areas reveal an underlying layer of clayey silt.
Looking north across the semi-stabalized beach to the cut bank in the spine of the spit. This bank, which is some 200 meters distant, is five to five-and-a-half meters high. It was established when the lake level was stable for a number of years in the 1970s. Since then, the lake has been retreating continually. On June 25, 1990, leveling showed that the shore of the lake was 510 meters from the base of the cut bank. The drop in elevation from the base of the cut bank to the lake shore is about 1.5 meters.
Just beneath the cut bank, a meter to a meter-and-a-half of wind-blown sand has accumulated, making the exposed part of the bank about four meters high. This is a high-traffic area as you can see from the many footprints, which here include hyena, hare, bird and lizard tracks. The circular composed of dark patches includes partially buried topi dung and the remains of a recent hearth.
The grass that stabilizes the beach and promotes dune formation is spread by herds of topi, who graze on the grass and broadcast its seeds in their dung. Notice how the roots spread out searching for entry into the substrate. In this case the substrate is wind-exposed beach sand that lies exposed about 100 meters from the shore.
This is the skull of a fisherman who drowned in a storm and washed ashore along with his small raft. It is included here because is shows how extensive the wind erosion is on the beach behind the shore. This photo was taken about 175 meters from the shore looking diagonally across the beach toward the cut bank. From the point where this photo was taken, there is about 100 meters of actively eroding beach in the direction of the of the cut bank (at right angles to the cut bank). The active zone of wind erosion is about 225 meters wide. The deposits beneath the beach are graded to the spine of the spit, i.e., the top of the cut bank, but the erosion surface is graced to the base of the cut bank, some five meters lower.
In 1990, there was 500 meters of beach with a cut bank five meters high. When you do the trig, this means that a 10 cm. cultural layer is exposed in a swath that is 10 meters wide and as long as the occupation was distributed parallel the the shore. And this is exactly what we find. At any given time an occupation eroding from the beach is exposed in an area about 10 meters wide and between 20 and 80 meters long.
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© 2008 by Charles M. Nelson
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