Geoscience Reference
In-Depth Information
Fig. 15.17
Shore-displacement diagram for the Mälaren area for the period 500 until 2000 AD
(after Amrosiani and Clarke
1998
, fig. 1)
sea-level curve for Lake Mälaren. Before the excavations, it was assumed that the
fall in sea level due to the isostatic land uplift should be regarded as a continu-
ous process without fluctuations. However, together with the results of the scientific
investigation of shore displacement in other parts of Lake Mälaren (Miller et al.
1997
, Risberg et al.
2002
), the Birka harbour stratigraphy and the finds from the
site present a different picture: the relative sea level fell rapidly during the eighth
and eleventh centuries AD, due to the isostatic land uplift, but rose considerably
in the tenth and twelfth centuries AD. For several decades, the Birka waterfront
experienced a transgression caused by a temporary fall in the eustatic sea level
(Ambrosiani and Clarke
1998
).
During the following centuries, the late Middle Ages and early modern times,
the changes in the relative sea level on the southern coast of the Baltic Sea remained
within the rate of annual fluctuation and are usually no longer detectable in the
archaeological record. This is in distinct contrast to the situation in the northern part
of the Baltic area, where the continuing uplift and shore displacement can still be
used to determine the chronology of coastal sites in these periods.
15.4 Summary
After the ice masses in the glaciers of the Fennoscandian ice sheet had melted,
the new landscape around the Baltic Sea basin began to be settled by human
communities. Due to the eustatic sea-level changes and the strong isostatic land
