Kariandusi Prehistoric Site
The Site:
The Kariandusi archaeological site lies on the eastern side of the Rift Valley some 120km NNW from Nairobi, and rests on the Nakuru-Elmentaita basin which occupies the width of the Rift valley, flanked by Menengai crater on the north and the volcanic pile of Mount Eburru, on the south.
Dating back between 700,000 to 1 million years old, Kariandusi is possibly the first Acheulian site to have been found in situ in East Africa and was gazetted as a national monument in 1954. There is enough geological evidence to show that in the past, large lakes, sometimes reaching levels hundreds of meters higher than the present Lake Nakuru (1,757m asl) and Lake Elementaita (1,776m asl), occupied this basin.
In between the upper and lower excavation sites is a deep dry gorge accessed by steps (see gallery photo) where the fascinating strata of the rock has been exposed by natural erosion by the river which used to pass through this gorge. From the ground level the main layers represent a prolonged dry period, a shorter volcanic period and overlying this the white diatomite sediment from a prehistoric lake bed.
The small site museum at Kariandusi displays excavated fossils and stone tools. There is also a molar of the straight-tusked elephant, a species of elephant that once existed in England and the rest of Europe before it became extinct.
A small fee is payable for entry to the site (currently Kshs 500 for non-residents, Kshs 250 for children)
Local geology:
Lake Elementaita is part of the Kenya Lake System (comprising Lakes Nakuru, Elementaita and Bogoria) a series of alkaline lakes on the floor of eastern arm (Kenya or Gregory Rift) of the East African Rift which formed as a result of major tectonic and/or volcanic events between 2 and 0.5 million years ago. During the late Pleistocene and early Holocene, Lake Elementaita was at times united with and expanded Lake Nakuru, forming a much larger dilute lake.
The area is characterized by steep fault scarps, deep gorges, step-faulted blocks, cinder cones and craters on the rift floor, gushing geysers and hot springs. The three lakes are ecologically, geologically and hydrologically connected and are essential to the hydrological cycle that contributes to geothermal energy which is tapped further to the south near Lake Naivasha.
John Walter Gregory, the first European to investigate the Rift and who named it, in 1893 deduced that this cataclysmic rent in the face of the earth was formed ‘by the rock sinking in mass, while the adjacent land remained stationary’. See here for a more detailed explanation with explanatory diagrams.
As the rifting process continues, the floor of the Rift (valley) continues to sink and thus the height above sea level of the Rift Valley lakes is much lower than in the (geological) past. Remnants of the former (joined) lakes are preserved as sediments at various locations around the lake basins, including former shorelines. It is within these sediments (which may be manifested as diatomite deposits, such as those at Kariandusi) that stone axes and fossils may be found, especially in areas like Kasiandusi where they have been exposed (and also transported) by the erosive action over time of (particularly flood) water in rivers and streams.
Fossils and Fossilisation:
A fossil is basically the remains of animal or plant that existed in an earlier age which has been turned to stone and fossilisation is the process by which this occurs. This is actually variety of often complex processes that enable the preservation of organic remains within the geological record.
It usually includes the following conditions: rapid and permanent burial/entombment (protecting the specimen from environmental or biological disturbance); oxygen deprivation (limiting decay and biological activity/scavenging); continued sediment accumulation as opposed to an eroding surface (ensuring the organism remains buried in the long-term); and absence of excessive heating or compression which might otherwise destroy it.
Fossil evidence is typically preserved within sediments deposited beneath water, partly because the conditions outlined above occur more frequently in these environments, and also because the majority (>70%) of the Earth's surface is covered by water. Even fossils derived from land, including dinosaur bones and organisms preserved within amber (fossilised tree resin) were ultimately preserved in sediments deposited beneath water, ie. in wetlands, lakes, rivers, estuaries or swept out to sea.
See here where a fish is used as an example to illustrate the stages associated with fossilisation within off-shore marine sediments.
Over time the plant or animal remains are gradually buried deeper by accumulating sediment. Slowly the weight of the sediment compacts the underlying areas, pressing the grains together, driving excess water out, and depositing minerals in the pores, and ultimately turning the soft sediment to hard rock - a process known as lithification.
As this process takes place, minerals contained within the waters-saturated sediment replace the original minerals in the skeleton and fill any voids formed as parts of the skeleton dissolve. The process of mineral replacement is known as permineralisation and results in a remineralised copy of the original skeleton.
After millions of years with the fossil rock buried deep within the bedrock, tectonic forces (such as those associated with the Rift) expose the bedrock. Erosion then gradually strips this away eventually revealing the fossil.
The Acheulean Tradition and Stone Tools:
This originated in sub-saharan Africa and subsequently spread across much of West Asia, South Asia, and Europe (see gallery for maps of distribution and main sites), It is an Old World Lower and Middle Paleolithic era culture, dated from about 1.76 million to 100,000 years ago, and characterized by a stone tool assemblage dominated by hand axes.
Acheulean tools are typically found with Homo erectus remains (see here for the characteristics of Homo erectus). It was the dominant technology for the vast majority of human history during this period (see here or here for more information on this).
Dr. Louis Leakey, the renowned palaeontologist and archaeologist (see here for a short biography), believed that Kariandusi was a factory site of the Acheulian period. He made this conclusion after numerous collections of specimens were found lying in the Kariandusi riverbed. This living site of the hand-axe man, was discovered by him in 1928 when he noticed stone tools projecting from a cliff on the site which was subsequently excavated between 1928-31 and again in 1947. A rise in the lake level had driven pre-historic men from their lake-side home and buried all the tools and weapons which they left behind in a hurry.
The site has several excavation pits displaying a scattered assortment of stone tools, cutting implements (mainly heavy hand axes and cleavers) made from obsidian, the black volcanic rock found in lave flows. There are also specimens made of a local trachyte lava. The tools are likely to have been used for butchering meat.
The hand-axe that was the main feature of the Acheulean tradition has been described as the Swiss Army knife of prehistoric man, because it seems to be a multi-purpose instrument. Hand-axes are suited to slicing, dicing, chopping, rooting and killing animals. It is a teardrop shaped stone, that has flakes chipped away from both sides of it, to produce a lens shaped piece, described as bifacial. The hand-axes could be anything from extremely roughly shaped, to beautifully carved. They are also a variety of sizes, for different purposes. Other types of Acheulean tools are cleavers, scrapers and picks.
The functional significance of the Acheulean tool industry has been debated, and several possibilities have been proposed: butchering large animals, digging up resources found in the ground, use as missiles against prey and/or predators, stripping bark to get at edible layers, use as "flake-dispensers" rather than tools. Whatever the tools were used for, the industry remained constant for about 1 million years.
Diatomite: Near the site is a diatomite mine where many tunnels have been excavated by hand to extract the diatomite, a fine white powder rock composed of almost pure silica. The mining has continually unveiled more archaeological materials and made it possible for the dating of the site by use of pumice and other datable materials in the sediments.
One interesting observation that Dr Leakey made was the fact that the diatomite found in Kariandusi (also found in certain other parts of Kenya’s Rift Valley) is the only one in Africa and also found in Germany but nowhere else in the world. In Kenya, the extent of the diatomite around Kariandusi provides evidence of the large lake that once covered lakes Elmentaita, Nakuru and Naivasha basins before shrinking to form the three present lakes due to faulting.
Diatomite consists of mineralized diatoms (aquatic microscopic plants or algae) that accumulate silica and carbonate deposits on their outer shells when alive; upon death, diatom skeletons accumulate on the lake bottom. The Kariandusi diatomite is mined and processed for use in many areas including filtering soft drinks, paints, insulation, toothpaste manufacture . . . and for face decoration by the Maasai.
Questions to answer:
1) In the dry gorge, what is the approximate width of the rock strata of the volcanic period? What is the colour of this layer?
2) At the lower site, according to the information sign, how is it thought that the over 1,000 stone tools found at this location may have got there? How do the hand axes here differ from those at the upper site? Why this might be? (The guide should be able to assist here)
3) Using your GPSs take an altitude reading at the site. What is the approximate difference between this and the current altitude of Lake Elementaita? (This will demonstrate how much the land has sunk over the years as a result of the ongoing rifting process).
4) Why would you expect to find fossils and archaeological materials in the diatomite layer exposed in the rock strata of this area?
5) One particular fossil, an example of which is seen at the upper site, is commonly found at hand-axe sites from England all the way to South Africa. What is it? What large creature did it come from?
6) (Optional) Take a photo of yourself at the site pretending to be homo erectus holding a hand axe!