Hafgerdingar: a mystery from the King's Mirror explained

• Published in: Polar Record
• Main Authors: Lehn, Waldemar H., Schroeder, Irmgard I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2003
• Subjects: Greenland; Mirages; Greenland Sea; Iceland; Polar Record
• Online Access: http://dx.doi.org/10.1017/s0032247403002924; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0032247403002924

The medieval King's Mirror describes Iceland and Greenland with a scientific accuracy that is remarkable. One of the very few exceptions is the hafgerdingar in the Greenland Sea. The term translates as ‘sea hedges,’ within which a mariner may become trapped at great peril. Many have believed that a real event was being described, although none of the proposed explanations has been totally satisfactory. The most common view currently is based on Steenstrup (1871), who explained the phenomenon as a tidal wave following a submarine earthquake. A simpler and more consistent theory is developed here: that the hafgerdingar are an optical phenomenon, specifically, a superior mirage. Such mirages, quite common in the polar regions, can produce an appearance fully consistent with the original description, as illustrated by several photographs and a computer simulation. Even the peril to seafarers has been corroborated, in the sense that such a mirage is frequently followed by a storm.