Towards a Baltic Sea Region Strategy in Critical ... - Helsinki.fi

CHAPTER VI: WATER
Hanko is also a popular summer resort with a coastline of some 130 km, of which
30 km are sandy beaches.
Geological and hydrogeological background
The shallow groundwater aquifer of the Hanko coastal area belongs entirely to the
First Salpausselkä formation (Figure 5). The primary sand and gravel formation
deposited in the front of the ice sheet into deep water in the end of the Weichselian
glaciation in time span of 200 years, 11 250 – 9 900 years ago (Fyfe 1991,
Saarnisto and Saarinen 2001). The form of this primary sand and gravel formation
was quite narrow and low (Fyfe 1991). When the ice sheet withdrew from the area,
this deep water sitting formation was covered by fine sediments - fine sand and
clay layers - of Ancylus Lake and the Littorina Sea. The sea level has been
regressive since the glacial period, caused by the isostatic land uplift - the only
exception to this was the transgression of Ancylus Lake and the Littorina Sea,
when the sea level rose for a while (Kielosto et al. 1996).
Figure VI—5 The Hanko case study area on the Quaternary deposit map. 115
After the area emerged, the Salpausselkä formation was exposed to sea waves and
wind. Therefore littoral sand deposits and fine sand wind deposits covered the clay
and fine sand sediments in places. The bedrock in the Hanko area consists mainly
of Precambrian crystalline igneous and metamorphic rock, strongly fractured along
115 Quaternary mapping data © Geological Survey of Finland; Base map data © National Land
Survey of Finland.
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