Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

Geological Survey of Finland, Special Paper 46
Peter Johansson
The deglaciation phase and the fi nal disappearance
of the Late Weichselian ice sheet were examined
in Finnish Lapland by studying different glacial
processes and their resulting landforms. These are
subglacial meltwater action and glaciofl uvial hydrography,
till stratigraphy and ice fl ow directions,
proglacial, marginal and lateral meltwater action
and the development and types of the ice lakes.
Tanner (1915) was the fi rst to study deglaciation
in northern Finland. The fi rst model of the retreating
glacial margin was created by him and is still valid
in a broad scale. Mikkola (1932), Penttilä (1963),
Kujansuu (1967), Johansson (1995) and many others
have by their research added more details to the
The Younger Dryas ice-marginal landforms in
northern Norway are situated only 20 kilometres
from northern Finnish Lapland (Sollid et al. 1973,
Andersen et al. 1995). The active ice fl ow stage of
Younger Dryas can be detected in Inari, northern
Lapland, which was considerably infl uenced by the
distinct ice lobe during the Younger Dryas (Punkari
1980). The extensive drumlin fi eld is related to this
fl ow stage and it extends as far as the Younger Dryas
ice-marginal landforms in Norway and Pechenga
area, NW Russia (Marthinussen 1962, Yevzerov &
Koshechkin 1980, Yevzerov & Kolka 1993, Yevzerov
et al. 2005, Semenova 2005). During this time
the so called younger till bed or Till Bed II was
deposited and occurs widely through the area. On
top of the Till Bed II there is a quite common even
younger till bed, known as Till Bed I or surfi cial
till (Hirvas 1991, Johansson 1995). Its deposition is
related to the ice fl ow during the deglaciation following
the Younger Dryas. In eastern Lapland the
youngest ice fl ow direction can be used to picture
the retreat of the ice sheet, because the retreat was
usually in the opposite direction to that of the last
ice fl ow. The network of subglacial glaciofl uvial
systems indicates the direction of the retreating ice
sheet even more accurately than the till fabric of the
surfi cial till. This is due to the fact that in subglacial
tunnels the meltwater tends to fl ow disregarding
any terrain obstacles toward the lowest pressure i.e.
the margin of the glacier. The subglacial meltwater
48
INTRODUCTION
YOUNGER DRYAS END MORAINE
picture of the deglaciation. Compared with southern
and central Finland, the advantage of studying deglaciation
in northern Finland lies in the fact that
most of the retreating ice sheet melted in a supraaquatic
environment, resulting in various kinds of
erosional and depositional landforms. Subaquatic
conditions existed only in the southwestern part of
Lapland because that area was covered by the waters
of the Ancylus Lake phase of the Baltic Basin. Some
small subaquatic areas exist in the northern part,
where the Arctic Ocean for a short time penetrated
into the river valleys of Teno and Lutto (Nikonov
1964, Saarnisto 1973) and into the Inari Lake basin
(Tanner 1915, 1936, Kujansuu et al. 1998).
action was mainly erosional at fi rst, forming channels
and gorges along the path of the conduit. Later,
deposition prevailed closer to the ice margin and it
was then that steep-sided and sharp-crested esker
ridges were formed (Fig. 1). The distribution pattern
of the Late Weichselian subglacial meltwater
system is radial (Fig. 2) and suggests that the direction
of the ice retreat was from the Younger Dryas
End Moraines in Norway and Russia towards the
ice divide area in northern central Lapland.
Fig. 1. The Pakajärvi esker is a typical subglacial esker ridge
with a sharp crest and steep sides.