Historical Perspectives to Postglacial Uplift

Postglacial land uplift has shaped the coastline of western Finland during past millennia. The first recordings of the consequences of the shoreline displacement due to land uplift date from the end of the 14th century. Current land uplift is mostly the result of the Weichselian glaciation, which ended about twelve thousand years ago, however, it is well possible that the process is also affected by the earlier glaciations of major ice ages having taken place up to hundreds of millions of years ago. In Finnish archaeology, coastline displacement has been used in dating the prehistoric settlements, as it can be assumed that these settlements follow the shorelines and waterways. By reconstructing the shoreline displacement and comparing the results with radiocarbon dating of findings from prehistoric settlements, new insights can be obtained from both the archaeology and the land uplift modelling point of view. In this chapter the geological and archaeological history of Satakunta is introduced by the example of four prehistoric sites in Lower Satakunta: Kolmhaara, Kuninkaanhauta, Luistari and Tyttöpuisto.

The rich and colorful human history of Eura has been documented based on archaeological findings. The oldest findings from Satakunta are associated with the Suomusjärvi culture, which may have had possible cultural and trading connections to East Karelia. The findings also show that there has been two different types of ceramics in the same place and time period indicating a chance that there have been two populations from different cultures at the same time. Numerous archaeological findings belonging to the later Kiukainen culture show the cultural dependencies with other archaeological finding sites in Finland. In this chapter, four archaeological examples that belong to either Suomusjärvi or Kiukainen culture are presented. Also a brief history of Scandinavian archaeology is presented and the roots of Finnish archaeology are discussed in this chapter.

The postglacial land uplift process has been modelled using two different approaches: by modelling the geodynamics of the earth’s crust (also referred to as Glacial Isostatic Adjustment (GIA) modelling) or by fitting mathematical models to existing archaeological and geological data (referred to as semi-empirical modelling). Although the semi-empirical models are not based on the physical properties of the earth’s crust, they are easy to implement and can adapt better to local variations when compared to the GIA models. Semi-empirical models are fitted to the ice retreat data, eustatic sea level dynamics and lake isolation data on past shoreline displacement. As most of these data sources involve uncertainties, the land uplift process can be modelled probabilistically using the Monte Carlo method.

The landscape reconstruction at four historical sites in Eura: Kolmhaara, Tyttöpuisto, Kuninkaanhauta and Luistari is presented in this chapter. The reconstruction focuses on the time periods of the archaeological findings at respective sites: Stone Age in the case of Kolmhaara and Tyttöpuisto, Bronze Age in the case of the Kuninkaanhauta and Iron Age in the case of Luistari. Landscape reconstruction results are discussed in relation with the radiocarbon datings of the findings at these sites. It is found that while for the Kuninkaanhauta the land uplift model locates the settlement at a favorable location with respect to the shoreline at approximately the same time period obtained using radiocarbon dating, there is a significant discrepancy between the two methods of estimating the age of the settlements for the Stone Age sites of Kolmhaara and Tyttöpuisto.

The challenges of land uplift modelling and determining the age of prehistoric settlements are discussed in this chapter. Land uplift modelling is a valuable tool for re-iterating the datings of archaeological findings, but the model and its source data must be constantly reviewed and adjusted when new data becomes available. Also, the erosion and sedimentation processes and local variations in land uplift should be taken into account when refining the land uplift model. On the other hand, the results obtained by radiocarbon dating are challenged by phenomena such as the water reservoir effect, for example.