The largest observed ridges were 6-8 m thick (Lepparanta & Hakala 1992), but it is probable that larger ones exist, in the eastern part of the gulf, near the fast ice boundary
at Kotka-Vyborg longitudes (Lepparanta & Wang 2002).
For the period 1930 through 1950, de la Mare finds that the sea ice boundary
remained stable, averaging around 61.
With increasing thickness, longer and longer fetches are needed to break the ice, which results in the shifting of the landfast ice boundary
further offshore during winter (see Fig.