It is a sunny summer day and a wooden raft full of people is floating at Kammarlahti in Lake Kuolimojärvi in South Karelia. A pump provides the background noise for the scene. There are rubber boats a few dozen metres from the shore and a diver is in the water. A second diver is resting in a rubber boat.
All this is part of the underwater excavations of the University of Helsinki, Nordic Maritime Group and the Finnish Heritage Agency. The aim is to find traces of Mesolithic and Early Neolithic sites (10,000–6,000 years ago) from under the bottom sediments of the lake.
“Archaeological sites from the Mesolithic are not yet known from this part of South Karelia. There are sites from later periods but in the early Stone Age, the shoreline of this lake was in an entirely different place than today,” explains Satu Koivisto who heads the excavations. She is an archaeologist and works as a postdoctoral researcher at the University of Helsinki.
The area is part of the terminal moraine formation known as second Salpausselkä, which, like the first Salpausselkä, runs through Finland from east to west. Both formations formed during the last Ice Age. Animals, followed by humans, arrived in the territory of present-day Finland along this formation after the last deglaciation.
“In the southern parts of the Saimaa lake system, water levels have been as much as 20 metres below current levels. There are many lakes in Finland that have experienced substantial fluctuations in water levels. In addition to Lake Kuolimojärvi and Saimaa, Vanajavesi and Pielinen are two additional examples of such lakes. This means that there are vast unexplored areas of prehistoric dry land that are now under water," Satu Koivisto says.
The second reason why Lake Kuolimojärvi was selected as a research area is because its water is exceptionally clear. Underwater visibility is good and no dust arises from the bottom.
The site is difficult and requires stamina and a broad range of expertise
An international team of ten people, comprising archaeologists and divers, is working at the site. The lightness of the Finnish summer means that the team can work ten hours every day.
“A multitude of different expertise is needed at excavations of this type. You must master all kinds of practical skills and you have a chance to explore things by hand and with your own eyes,” says Minna Koivikko, a maritime archaeologist at the Finnish Heritage Agency.
One diver works between one and one and a half hours without interruption. They wear a quilted suit under a dry diving suit because it gets cold quite quickly under the water. They carry a large number of tools, such as a trowel, a video camera and a suction mouth of the dredge through which the sediment from the bottom is removed and released to a net bag. The bag and its contents are lifted to the raft and examined.
The divers are assisted by the archaeologists on the raft and in the rubber boats who operate the tubes, pumps and the sieve. The archaeologists make a preliminary examination of the material after which all interesting items are taken to the mainland for further study. All remaining materials, mostly pebbles, are thrown back to Lake Kuolimojärvi.
Video: Satu Koivisto examines sediment from the lake bottom.
On the first days of the excavations, the ‘catch’ mostly consisted of fragments of information about the sedimentation history of the lake environment. This is because at that stage, the divers were still dealing with bottom sediments at a depth of between 1.5 and 2 metres.
“However, we have already received clear evidence that the water level is now much higher than in the past. We have also found charcoal but that may be the result of forest fires that have occurred more recently,” Satu Koivisto explains.
New methods and discoveries
As the person in charge of the research project, Satu Koivisto is responsible for its scientific aspects and coordination and for ensuring that all goes as planned. She is not working as a diver in the project. She is interested in peatlands and other watery environments where organic materials, such as wooden structures may have been preserved.
“The more challenging the excavation site, the more interesting it becomes. For this reason, I’m interested in mires and lake bottoms. In fact, one purpose of this project is to develop methods for exploring such demanding burial environments.
Jørgen Dencker, an experienced Danish underwater archaeologist, works at the excavations as an expert on underwater Mesolithic sites and excavation techniques. His main role is to assist the team with the use of the underwater equipment.
Dencker has carried underwater excavations in different parts of the world.
“This was definitely a good and sheltered place to live in during the Stone Age. There is a great deal of archaeological potential at this site. If there is something under the sediments, we’ll find it,” Dencker assures.
He was right. At the start of the second week of the excavations, the divers found a hearth structure and quartz flakes in a test pit at a depth of nearly one metre. They are the remains of a now submerged settlement.
Future research at the site will provide us with a clearer picture of human occupation in South Karelia in the Mesolithic and Early Neolithic periods. The discoveries made by the research team also open up a new research path in Finnish archaeology.
“Using the excavation methods tested at Lake Kuolimojärvi we may also be able to find other sites in lake environments that have a similar history as Kuolimojärvi and Saimaa,” explains Satu Koivisto.
Video: Archaeologist Eveliina Salo working at the lake bottom.