202 THORODDSEN 



fjords have been filled up even within historic times, and several 

 large parishes and districts have been destroyed. Oraefajokull has, 

 in the same manner, caused considerable destruction; while the 

 waterfloods of Skei5ararjokull, which were especially frequent during 

 the 19th century, have done less material damage, as only unin- 

 habited sandy wastes were inundated. Minor glacier-bursts are also 

 occasionally due to lakes and rivers, which have been dammed by 

 glaciers, suddenly breaking through their barriers and inundating 

 the district. These glacier-bursts have a great effect upon the plant- 

 life, because no permanent vegetation can exist upon gravelly and 

 sandy flats which are constantly inundated by waterfloods carrying 

 large pieces of ice; therefore very large stretches of lowland in the 

 neighbourhood of such volcanoes and glaciers are destitute of plant- 

 growth, for what little vegetation appears in the period between the 

 glacier-bursts is quickly destroyed. The general physiographical con- 

 ditions pertaining to the glaciers of Iceland may be best seen by 

 a study of the table opposite. 1 



Snow-line. In Iceland it is not easy to determine the snow- 

 line, owing to the great variability of the climatic factors. Because 

 of the great annual and periodical variability of temperature and 

 of the circumstances connected with precipitation, the snow-line also 

 varies. In Iceland three kinds of height-levels connected with the 

 vertical distribution of the snow, and dependent on climatological 

 and orographical conditions, may be supposed to exist. The snow 7 - 

 line proper, which signifies the lowest limit of the permanent, con- 

 tinuous snow-covering of the mountains, is not subject to very great 

 changes from year to year. Below 7 this comes a zone of detached, 



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more or less closely placed, patches of neve and wreaths of snow 7 ; 

 these never melt entirely, but either are added to or else diminish 

 according to the character of the year. Below this zone comes the 

 most variable of the snow-coverings: scattered snow-drifts which 

 to a greater extent than the others are dependent on orographical 

 conditions. These snow-drifts may persist through a series of 

 damp and cold years, but dwindle almost to nothing or disappear 

 entirely in warm and dry years. The snow at Drangajokull upon 

 the north-western peninsula may serve as an example. Here, on 



1 Here it should be noticed that many of the figures for the area of the 

 Jokulls are approximate and given as a rough estimate, because the maps of a 

 great part of Iceland, and especially of the plateau are still very imperfect. 



