Sea-ice already thick enough for cars, at least in theory

Ice on the Gulf of Finland now stretches 50km south from Helsinki towards Tallinn

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By Kari Kiuru
     
      Back in early December, when the golfers were still out playing in Finland, some may have thought it would never happen this year, but the ice off the coast of Helsinki is already strong enough to carry skaters, skiers, ice-fishermen seated around their little holes, and yes, even a car.
      This last notice does not mean that Merentutkimuslaitos (the Finnish Institute of Marine Research) is actively encouraging people to go for a drive on the ice, because anyone who does must also know his or her way around the places with strong currents or where the condensation water from power stations is pumped out. At spots like these the ice under the covering of snow can be treacherously thin.
      Right now the sheet ice on the Gulf is between 15 and 30 cms thick. There is a solid sheet of ice stretching roughly 50 kilometres south from Helsinki towards Tallinn and the Estonian coast. Where shipping lanes cross it, the ice is naturally not for walking.
     
"Out at sea, the ice thicknesses vary considerably. Roughly 30 centimetres of ice will bear a load of 3,600 kilos, but take off ten centimetres and the bearing capacity drops down to 1,600 kg. By and large the ice will carry these loads, but currents can eat away the ice cover from underneath", warns researcher Ari Seinä from the Institute of Marine Research.
      The ice can be expected to thicken up still further for another month or so. By the end of the winter, the average thickness of ice off the coast of Helsinki has been 38cm, but out in the Gulf, half a metre and more is by no means unheard of.
      From mid-March onwards, the ice starts to weaken, and in front of Helsinki the ice surface has usually broken up and disappeared by the middle of April.
     
According to Ari Seinä, the ice conditions this winter are more or less normal. Last winter started in much the same fashion, but a very cold spell in early March brought a sudden thickening of the ice-cover.
      In most years the Gulf of Finland will freeze over completely. In a mild winter the effect may be incomplete, but if we have a year with heavy and sustained frosts the ice-cover can stretch right down to Bornholm and the Danish straits - the Great Belt, Little Belt, and Oresund. In 1987, the ice sheet covered around 405,000 square kilometres, but two years later the figure was just 52,000 sq km, with only the eastern end of the Gulf of Finland and the northern part of the Gulf of Bothnia under ice (see second link, "Ice Winter").
      There is no real way of predicting the extent of the ice at the beginning of the winter. It is only around the end of January that any accuracy can be attached to forecasts.
     
Helsingin Sanomat / First published in print 24.2.2007


Links:
  Finnish Institute of Marine Research
  Ice situation (.pdf file)

KARI KIURU / Helsingin Sanomat
kari.kiuru@sanoma.fi