The next best known of the Icelandic volcanoes is perhaps Kötlugiá, which has erupted no less than fifteen times since the year 900. It now presents nothing but a deep valley filled with snow, cutting into the very heart of Myrdals Jökull; it is one of the largest examples of breached craters in the world. The principal phenomena attending eruptions of this volcano are stupendous floods of heated water and the prodigious quantities of sand ejected. It has, I believe, never been known to produce lava, but upon the base of the mountain I found numerous ancient lava streams, proving that at one time Kötlugiá was no exception to its neighbouring volcanoes. The floods from Kötlugiá during eruptions have often submerged a district of 280 square miles, continuing sometimes for days, in spite of the rapid outflow to the sea. These floods are produced not only by the melting of the snow at the time of eruption, but in all probability by the bursting of large cavities in and beneath the mountain, in which water might have been for years accumulating. This aqueous phenomenon is, however, by no means peculiar to Kötlugiá, although it occurs on the largest scale, for during the 13th and 14th centuries all the volcanoes in the south of Iceland erupted water. The most extensive eruption that ever occurred in Europe during historic times proceeded from the south-west portion of the Vatna, named the Skaptar Jökull. This volcano has only been known to have erupted upon that occasion, viz., A.D. 1783, when it produced two of the most extensive lava streams in Europe. The highest volcano in Iceland is Örœfa Jökull, which reaches the height of 5927 feet.
The volcanoes which erupted so violently in the spring of 1875, and one of which wrought such damage in the north of Iceland, are--the Öskjugjá (or the chasm of the oval casket), situated in the Dyngjufjöll mountains upon the north of the Vatna, and a chasm some twelve miles in length, which opened in the Mývatns Örœfí (or sandy desert of Mývatns), but as these have already been described at some length I need only casually mention them.