Rit (Vísindafélag Íslendinga) - 01.06.1975, Blaðsíða 26

ing reasons. The higher moisture content of the soil, a more solid
ice cover and to some extent the vegetation. 1) It is evident that
mounds generally do not form where conditions are very moist.
Conceivably the most reasonable explanation is that the soil parti-
cles, when partly afloat, cannot be fused together so as to form
chunks or nuclei, which later would mark the beginning of a
mound. In this connection I would like to call attention to the fact
that wherever water is used to irrigate mound pattemed mires
they level out amazingly soon. This was ohvious during the first
years of the Flói Irrigation Project, and as a matter of fact through-
out the country, where irrigation was practised. 2) The flói areas
are normally covered by a thick ice sheet in winter, the snow cover
on the other hand is not much thicker than in normal mires. Fre-
quently the flói tract freezes over, particularly if it is high in mois-
ture content, early in the fall, before the frost penetrates the soil,
and the ice sheet often does not thaw until after the snow has
melted away in spring. If this view is correct (Tanttu et al.) i.e.
that mound formation is primarily caused by different degrees of
expansion in the soil when it freezes, it is understandable that there
is little mound development under the ice roof. The ice alleviates
the chill effect of the climate, but what is probably more impor-
tant is that the ice roof contains the soil and impedes its move-
ment, as if it were in a straitjacked. 3) In the flói area there is less
moss vegetation than in the mýri, and this decreases mound forma-
tion, because the moss always exerts some influence on the mound
formation of the mýri.
Formations
It. has been mentioned previously that the flói areas in Iceland
are originally topogene, in some parts, however, where precipita-
tion is heaviest and the flói tracts most extensive, it is possible that
they are to some degree ombrogene, but their vegetation rarely
resembles the ombrogene mýri. In flói areas there are always ponds
and small lakes, sometimes even fairly large lakes (Mýrar). The
flói tracts have originally developed out of lakes and ponds, which
have been filled up in an infraaquatic fashion whereby mineral
matter and plant rests have been deposited in them either as bottom
sediment or the lakes have been filled up with material from the
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