Late Holocene land uplift/neotectonics on the island of Valamo (Valaam), Lake Ladoga, NW Russia

The emergence of eight small lake basins from the Lake Ladoga basin waters in the Island of Valamo (Valaam), NW Russia was studied to work out the Late Holocene uplift history of the area. All eight small lake basins in the Island of Valamo (Valaam) emerged from Lake Ladoga when the water level fell 12 m in connection of the formation of River Neva, the current outlet of the lake. The consistent Valamo data is in harmony with the results from Kilpolansaari, north-western Lake Ladoga and show that River Neva originated 3100 14C BP, in corrected radiocarbon years at 3350 cal BP. Since the origin of River Neva, the island of Valamo has been uplifted 3–3.5 m more than the Neva threshold area at Porogi, as shown by the tilted transgression shoreline of Ladoga before the Neva was formed. One millimetre difference in annual uplift during the past 3000 years, which is the difference in the current uplift rate, explains this height difference, suggesting passive neotectonics in the area during the Late Holocene. This result conflicts with Russian geodetic measurements showing anomalously high uplift rates, up to 6.4 mm/y, in the north-east Ladoga area, where uplift values are 1–2 mm/y according to Fennoscandian isobase maps. The above land uplift anomaly within Precambrian shield terrain far from the uplift centre around the Gulf of Bothnia would be difficult to explain. The isobase maps of present-day Fennoscandian uplift indicate a highly regular dome-shaped uplift pattern with no anomalies at a regional scale. The suggested anomalous Holocene uplift discoveries in the Gulf of Finland and southern Gulf of Bothnia areas are challenged, whereas strong palaeoseismicity resulting from rapid land uplift, immediately following deglaciation of the Scandinavian Ice Sheet, resulted in earthquakes, bedrock dislocations and massive rock falls, e.g. in the northern Lake Onega area and Lapland.