Rit (Vísindafélag Íslendinga) - 01.06.1975, Blaðsíða 17

driest, the mounds will be largest, and the mound size is determined
by the moisture content. This same phenomenon is mentioned hy
Jóhannesson (l.c., p. 48) who states: “it appears that any given
set of soil and soil moisture conditions will lead to a certain, well
defined frost heaving action and lateral soil movements creating a
fixed mound size for a given vegetative cover.”
2. Ice Cover. Ice formation in mýri in wintertime is in direct pro-
portion to their moisture content. It here becomes evident that
areas suhject to prolonged ice cover are relatively level. This, how-
ever, is not a universal rule, for I know of stretches of pattemed
mýri which are under average conditions in winter covered with ice.
3. Snow Accumulation. There seems to be no doubt that there
!s a relationship between the thickness of the snow cover in winter-
hme and mound formation. It is reasonably safe to conclude that,
rf frost is one of the main factors in the formation of mound pat-
terns, as most authorities admit, then its effect must he negligible
where the ground is covered by a thick cover of snow from early
Jall, before the ground is subjected to any considerable frost, until
late spring. This is obvious in mýri tracts alongside ridges and
hills. During the first snowfall snow drifts form in the concavity
at the bottom of the slope and there the drifts remain until spring.
Where the drifts lie we find a level stretch of mýri, beyond which
point the mounds prevail when the mýri proper is reached. Similar
phenomena occur in snowbound districts. There the mýri tracts
are generally more level than where the snowfall is less, in con-
nection with which attention may drawn to coastal districts on the
promontory between Eyjafjörður and Skagafjörður. I believe that
fhe snow cover is primarily responsible. However, the summer tem-
perature may be of some significance in this respect. As far as I
know highland mýri tracts are less patterned than those on the
lowland, with the exception of tundra moors, which will be dealt
with independently.
d*. The Plants. There is little doubt that some plants cause mound
formation. There are few of these among the phanerogams in mýri
tracts, but moss evidently plays in many areas an important role
111 mound formation. This applies to those locations in which
Spagnum thrives to some extent, where the moss always forms
mmor mounds on a surprisingly level base.
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