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(a)
(b)
Fig. 16.6 Pockmark structure in the eastern Gulf of Finland. a VSEGEI side-scan sonar image; b
fragment of echo-sounding profile, joint cruise of the Geological Survey of Finland and VSEGEI
on board R/V Aranda
of these structures is similar to pockmarks found in some areas of the Baltic Sea
and the Norwegian fiords (Jensen et al. 2002 , Plassen and Vorren 2003 , Söderberg
and Flodén 1991 ) , but the origin of these structures is debatable and needs addi-
tional detailed investigations. The pockmark distributions and their formations
can be, for example, important for the construction of the Nord Stream pipeline
because an interaction of natural phenomena and technological constructions can
have unknown consequences.
16.5.2 Exogenic Processes
Exogenic processes are more important as potential hazards in the coastal zone of
the eastern Gulf of Finland.
16.5.2.1 Coastal Erosion
The rectified length of the shoreline of the Russian part of the Gulf of Finland (sker-
ries and islands are not counted) is about 520 km. Traditionally, the coastal zone of
the easternmost (Russian) part of the Gulf of Finland was not considered as an area
of active litho- and morphodynamic processes, but recent study has revealed that
this area is under severe erosion. More than 40% of this coast is seasonally eroded,
which causes land loss and destructions of buildings and roads.
Some parts of the coastal zone are rather stable. The northern coast (between
the town of Primorsk and the Russian-Finnish border) does not suffer from wave
impact due to geological structure of granite and glacial till skerries and tectonic
uplift. Inner parts of the large bays (Neva Bay, Luga Bay, and Koporsky Bay) are
more stable due to relatively high sediment flux of the rivers Neva, Luga, and Sista
(e.g., annual suspended material flux - the Neva: 514,100 t; the Luga: 40,800 t; after
Raukas and Huvarinen 1992 ) . In the other parts of the studied coast, erosion rates
reach hazardous level.
 
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