Fróðskaparrit - 01.01.1998, Blaðsíða 167

SEINHOLOSENA VEÐURLAGIÐ ELVDI TIL JARÐFORMANDI VIRKSEMI í FØROYUM 173
mussen, 1986). Assuming a postglacial eu-
static sea level rise of about 125-130 m (Pi-
razzoli, 1996), the mean regional maxi-
mum Weichselian ice thickness can not
have exceeded 350-400 m, as there are no
late Weichselian or Holocene-age raised
beaches on the Faroe Islands (Humlum et
al, 1996).
Little is known about the late Weich-
selian deglaciation of the Faroe Islands.
Most investigations note a conspicuous
lack of recessional or readvance moraine
systems; only dead-ice features and ancient
medial moraine accumulations have been
described from certain major valleys on
Streymoy (Sugden and John, 1976); Jør-
gensen and Rasmussen, 1986). However, a
series of rather small, but distinctive,
moraine ridges relating to a final valley and
cirque glaciation was recently described by
Humlum et al. (1996). By comparing with
reconstructed Loch Lomond equilibrium
line altitudes from Scotland, a tentative
Younger Dryas age was suggested for these
moraine systems. Proper dating of the
moraines has not yet been successful, and
when the Faroe Islands became ice-free in
the late Weichselian is therefore still un-
known. The oldest relevant 14C date, ob-
tained from a lake-bottom core near Tórs-
havn, gives an age of 9,660±150 BP (14C-
years; Jóhansen, 1975; 1985). There is no
indication of any Holocene reglaciation in
the Faroe Islands (Humlum et al., 1996),
and probably, the islands have been ex-
posed to cold, non-glacial (periglacial)
conditions for the last 10000-15000 years.
The early Holocene (Preboreal 10000-
9000 14C-yrs BP) climate on the Faroe Is-
lands was arctic-subarctic with the arrival
of plant species such as Betula nana
(Jóhansen, 1985). In Boreal times (9000-
8000 14C-yrs BP) the climate changed to-
wards more oceanic conditions, with disap-
pearance of Betula nana. Plant species such
as Juniperus and Salix expanded, covering
the lowlands, together with tall-herb vege-
tation and grass heaths. The Atlantic period
(8000-5000 14C-yrs BP) was wet, with evi-
dence of strong leaching of soils. Peat be-
gan to accumulate, especially on high
grounds. From the onset of the Subboreal
(5000-2500 14C-yrs BP), climate became
cooler and wetter leading to widespread
peat formation and decreasing frequency of
Juniperus and Salix. Subatlantic time
(2500-0 14C-yrs BP) brought the arrival of
man in possibly two phases, AD 600-700
and AD 800-900, most likely monks from
Ireland and the Vikings, respectively, al-
though researchers do not entirely agree on
this issue (Mortensen, 1994; Haywood,
1995). The Subatlantic period was punctua-
ted by the so-called Little Ice Age (roughly
AD 1300-1900).
With the exception of few, isolated
stands of Betula pubescens (dated to about
4300 BP, Jóhansen, 1989), there have been
no natural forests on the Faroe Islands dur-
ing the Holocene, and the predominant veg-
etation is of the heath type. In particular
grass heaths are widespread (Tuhkanen,
1987), and give the islands their characte-
ristic green summer appearance. The graz-
ing of sheep (about 70000) may have con-
verted areas originally covered by dwarf-
shrub heaths into grass heaths (Giming-
ham, 1964).