Over the past millennia, the landscape has changed more in Finland than practically anywhere else in the world. The continental ice sheet of the Ice Age pushed the crust of the earth down and after the melting of the ice it began to return to its former position. The land originally rose at a very fast rate, estimated to have been at a maximum of 10 cm/year, i.e. 10 metres in a century. Land uplift was just as fast in Northern Scandinavia, but differences in elevation were greater there, where the present coast can be within sight of the Stone Age shoreline. In Finland, the distance can be hundreds of kilometres.




At the south-east end of Summassaari island is an impressive natural sight known as Haikankärki point. It belongs to a long series of ridges originating in the region of Central Ostrobothnia and continuing via the city of Jyäskylä to the Satakunta region. It formed in the final stages of the last Ice Age in the channel of a river flowing inside the glacier.

The continental ice sheet was at its thickest in the northern part of the Gulf of Bothnia. Accordingly, land uplift is fastest in this region. The rate of land uplift in all directions from this area. The boundary where no more land uplift occurs is reached in the Baltic countries and Denmark.

After the retreat of the ice, Central Finland was not the lake district that it is today, but instead the archipelago of the Yoldia Sea, the predecessor of the present-day Baltic. Extending from present-day Central Ostrobothnia in the north to Heinola in the south was a long, labyrinthine bay with islands following the present-day direction of Lake Päijänne and the lakes to its north. This bay gradually developed into a large lake because of land uplift, which is fastest in the above-mentioned part of the Gulf of Bothnia. The straits at the mouth of the bay in present-day Central Finland were closed by 6800 BC, and the former bay became Ancient Lake Päijänne, extending from the northern parts of Central Finland to Heinola. This lake discharged into the Ancylus Lake, a predecessor of the Baltic, through the headwaters of the present-day River Kalajoki towards the north. Around 8700 the Yoldia Sea had evolved into the Ancylus Lake as land uplift had closed the strait in Central Sweden that had linked the sea to the ocean. The melting of the ice sheet, in turn opened the straits of Denmark ca. 7000 BC. Other things were taking place around this time in the Lake Summasjärvi areas. The combined body of water of present-day lakes Summasjärvi and Kiimasjärvi, which was joined by a narrow strait was isolated from the Litorina Sea, the stage of the Baltic at the time. Secondly, the human occupation of the Voudinniemi and Rusavierto sites began.

Owing to faster land uplift towards the north-west, the waters of Ancient Lake Päijänne began to rise. Water-levels rose so much that for a brief time Lake Summasjärvi was again part of Ancient Lake Päijänne, until the latter found a new discharge channel in 5000 BC through the Heinola Esker into the present-day River Kymijoki. When this happened, water level sank immediately by several metres and new small lakes formed in the northern parts of Ancient Lake Päijänne. Towards the end of the Stone Age. The northern parts of Lake Päijänne formed permanently in the present region of Jyväskylä.

Lakes Summasjärvi and Kiimasjärvi were separated around 1900 BC. Major momentary change took place when the surface of Lake Lannevesi suddenly sank by four metres, when its waters broke through a threshold at Kirkkoharju Ridge. This caused short-term flooding but the effects were otherwise limited. Owing to the location of the discharge channel of Lake Summasjärvi the shore has slightly receded in the north part of the lake since the middle stages of the Stone Age, while the south part of the lake it has remained almost in the same position. Visitors to the Stone Age Village can admire the landscape in quite the same appearance as seen by Stone Age people in the area a few thousand years ago.


How Lake Summasjärvi area has changed over the past 11000 years?