Stormfloden 13.-14. november 1872

The most devastating storm surge recorded in the western Baltic Sea in the period between 1826 and the present occurred on 13 November 1872. In order to better understand such extreme Baltic surge events, spatial and temporal high-resolution grid values of atmospheric pressure and wind vector data for the North and Baltic Seas have been calculated.

Historical records of water level have been approached in an iterative process of modelling water levels based on present-day topography and by adjusting atmospheric pressure. The model system used is the BSH's operational model, which covers not only the Baltic Sea but also the North Sea and the Northeast Atlantic.

Therefore, the reconstructed atmospheric pressure field extending to 66.50° N and 10.00° W was supplemented with the EMULATE data set (Ansell et al. 2006).

The oceanographic part was a computation of boundary conditions for the 1872 tides.

Supported Assumption

Within the framework of the MUSTOK project (Die Küste 75, 2009), sub-project MUSE-Ostsee, the available assemblage of extreme floods in the western Baltic Sea has been enlarged in order to determine probabilities of occurrence for extreme storm surge levels which have not yet occurred in the past.

An analysis of simulated storm surges and of the reconstructed 1872 storm surge supports the assumption that minor changes in the force, direction, spatial extent and temporal evolution of the strong wind field over the Baltic Sea are enough to cause a transition from high to extremely high surge levels in the western Baltic with its small-scale topography.

Rejected Assumptions

A commonly held assumption is that additional mechanisms are involved in turning a high storm surge into an extremely high storm surge, especially in the case of the observed high water levels of November 1872, which were not reached during the MUSTOK project. At least with respect to 1872, we rejected the idea of water piling up in the Baltic prior to the storm and raising the flood level as it flowed back. Firstly, there was no continuous water transport into the Baltic during the entire period preceding the storm. Rather, there were periods of return flow. Secondly, when starting with an artificially filled Baltic Sea, simulated water levels were nearly unchanged.

Even omission of the storm of 12 November did not change the water level that was finally reached on 13 November. At the end of the storm of 7 November 1872, a rapid increase of water level was observed in Kiel. The effect in Kiel was even more pronounced after switching off meteorological forcing over the Northeast Atlantic, North Sea and Baltic Sea at the time of maximum water level in St.Petersburg. However, numerical experiments made by other authors (Jönnson et al. 2008) and for other MUSTOK cases put into doubt their interpretation as basin-wide seiches of the Baltic.

(1) Bundesamt für Seeschifffahrt und Hydrographie, Hamburg, Germany (ingrid.bork@bsh.de)
(2) Deutscher Wetterdienst, Hamburg, Germany (gudrun.rosenhagen@dwd.de)
(3) Bundesamt für Seeschifffahrt und Hydrographie, Hamburg, Germany (sylvin.mueller-navarra@bsh.de)

ABSTRACT
Beach-ridge systems are important geo-archives providing evidence for past wave climate including catastrophic storm flood events. This study investigates the morphological impacts of the 1872 Baltic storm flood on a beach-ridge system (sandy spit) in south-eastern Denmark and evaluates the frequency of extreme storm flood events in the area over a longer time perspective. This paper combines field studies of morphology and sedimentary deposits, studies of historical maps, digital terrain model, ground-penetrating radar profiles, and luminescence dating. Sea water reached 2.8 m above mean sea level (amsl) during peak inundation and, based on studies of the morphological impacts of the 1872 storm flood, the event can be divided into four phases. Phase 1: increasing mean water levels and wave activity at the beach brought sediments from the beach (intertidal bars and normal berm) higher up in the profile and led to the formation of a storm-berm. Phase 2: water levels further increased and sediment in the upper part of the profile continued to build up the storm-berm. Phase 3: water levels now reached the top of the dune ridge and were well above the storm-berm level. Sea water was breaching the dune ridge at several sites and wash-over fans were generated until a level where the mean water level had dropped too much. Phase 4: the non-vegetated wash-over fans functioned as pathways for aeolian sand transport and relatively high dunes were formed in particular along the margins of the fan where aeolian sand was trapped by existing vegetation. The studied beach-ridge system records about 4500 years of accumulation; the storm flood sediments described are unique suggesting that the 1872 Baltic storm flood event was an extreme event. Thus studies of beach-ridge systems form a new source for understanding storm surge risk. Copyright © 2013 John Wiley & Sons, Ltd.

Den ualmindelige Hastighed, hvormed Vandfloden steg, og den Ødelæggelse, som den frembragte overall, gav imidlertid en heldig Anledning til, at en stor Mængde Mennesker paa alle, de hjemsøgte Punkter holdt nøje Udkig med , hvorledes Vandet steg og faldt. Fremdeles gav Vandflodens overordentlig hurtige Stigen, der ikke syntes at staa i Forhold til Stormens Magt, derhos Anledning til forskjellige Forestillinger om den sandsynlige Aarsag til dette skrækkelige Naturphænomen , hvis Lige Ingen havde kjendt; thi vel var Stormen
meget stærk, men den var dog i det Hele ingenlunde haardere eller mere orkanagtig, end man undertiden havde havt den, idet Stormen hverken afrev Tagsteen af Bygninger eller omblæste Træer i nogen betydeligere Grad, end tidligere ofte var skeet, uden at en saadan
Vandflod deraf havde været en Følge. Temmelig almindelig blev det derfor antaget, at Vandfloden til en væsentlig Deel i det Mindste havde sin Grund i en Jordrystelse, som sagdes at være følt paa Bornholm og som formentes at have sat Østersøens Vand i en saa pludselig og stærk Bevægelse, at Stormfloden deraf havde været Folgen.

Colding mener at årsagen til stormfloden var et jordskælv, medens Martin Ekman mener, at jordskælvet var en følge af stormfloden.