Suur Strait (Moon Sound, Moonzund)

July 9th, 2011

TALLINN, ESTONIA–The Wooster Geology team in Estonia successfully returned to the Estonian capital city of Tallinn today, which means we crossed by ferry the Suur Strait between the western Estonian islands (notably Muhu) and the Estonian mainland. This is an interesting strip of water with a complicated geological and human history.

There is an Estonian dream of building a bridge or digging a tunnel across the Suur Strait to eliminate the need for the ferry line and more efficiently connect Muhu and Saaremaa to the main part of Estonia. It will not be an easy task (and it is probably too expensive to ever be attempted), but it has led to considerable study of the strait and its oceanographic, biologic and geologic characteristics. The currents are complicated as they move between the Gulf of Riga to the south and the Baltic Sea proper in the north, and it freezes solid in the winter (when it is crossed by a 9 km long ice road). The strait hosts one of the most significant bird migration routes in northern Europe, and the marine fauna and flora here is still poorly surveyed.

The floor of the Suur Strait is highly variable from exposed Silurian limestone bedrock to thick mantles of glacial till. As you can deduce from the Google Earth image, some parts of the strait are very shallow, and the deepest regions are no more than 21 meters of water. Because of isostatic rebound, the region gets shallower about 2 mm per year as the land rises.

Suur Strait as viewed from northeastern Muhu (July 2007).

Historically, the Suur Strait has been the “backdoor” to the Gulf of Riga to the south. Any navy that controls the Baltic wants to keep that backdoor open for itself, but close it to enemies. This was especially the case during World War I when the Imperial German Navy sought to trap elements of the Imperial Russian Baltic Fleet in the Gulf on October 17, 1917, during Operation Albion. Most escaped north through the Suur Strait (known then in English as Moon Sound) following carefully dredged channels lined with mines. One Russian battleship, the Slava, was severely damaged and took on too much water to pass back through the shallow strait and was scuttled.

The Suur Strait was crossed by the Germans in 1941 as they invaded the western Estonian islands (Operation Beowulf), and again by the Russians when they re-invaded in 1944 (Moonzund Landing Operation).

We made it across on one of the car ferries which ply the Suur Strait between Kuivastu and Virtsu. Like the Russian warships of old, it also follows a dredged channel through the shallow and storied waters.

View from our ferry west across the Suur Strait towards Kuivastu on Muhu island. Last ferry ride of the trip!

Reference:

Saaremaa Fixed Link – Report of Preliminary Environmental Impact Assessment – Final Draft – 15.07.2005 (Google this and you can get a thorough report as a pdf.)

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