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14
Matti Sauramo, The mode of the land upheaval in Fennoscandia.
By means of varved sediments he has accounted for the recession of
the ice-border and also for the changes of level, when the delta-planes
of the rivers during the regression moved from their highest position
down the valleys. The oldest beach features formed on the coast of
the Bothnian Gulf at the retreating land-ice represent chronologically
and also in their relation to the first Littorina beach that stage, when
the rapid regression after the fourth Yoldia set in from an elevation
of about 270 m. at Linnamon. From this height the sea level has moved
downwards 71 metres, near to the first beach of the Ancylus lake.
This occurred about between the years 950 and 1 500 according to
the Finnish chronology. Thus the mean velocity of the regression is
13 m. per century. This figure exceeds all other values relating to
the land uplift in Fennoscandia and is in the opinion of the author
valid only for Ångerman land at the close of the Ice Age. At the same
time the zone of the hinge-line in Western Finland, lying at a distance
of 400 km. from Ångermanland oscillated up and down within
narrow^ limits, also later on still remaining at the same elevation, as
seen from observations made by Aurola (1938) and the author
(Sauramo 1936, Fig. 7). These facts give a striking conception of the great
and abnormal temporary tilting in question. The eustatic rise of the
sea-level has played no decisive role in this case.
We must, however, remember that the above mentioned figure
relating to the regression in Ångermanland is the mean amount
for 550 years. Actually, the change of level was not continuous, but
intermittent, the formation of distinct beaches corresponding to
pauses in the regression. The sea-level has thus for instance remained at
the first Yoldia beach for about 400 years and at the fourth Yoldia
for about 350 years. The above mentioned 550 years include the
formation of the well marked Rhabdonema beach and also some other
less distinct shore features. For these pauses in all about 400 years
must be calculated. Consequently there remains only about 150
years for the movement itself, assuming that the land rise was not
continuous as in the east of the Bothnian Gulf. Here, at Mount
Lauhavuori, the above mentioned figures are in every case usable,
being only a little smaller than in Ångermanland. This means that
the actual velocity of regression was from 40 to 50 m. per century,
or 0.5 m. in a single year! That is nothing less than earthquakes.
Such a conclusion is not at all surprising, considering that even
now the centre of land-upheaval in Fennoscandia coincides with an
area where the earthquakes are most numerous and strongest
(Sahl-ström 1930). As supposed by Renquist (1930), they may be connected
with the recent uplift of the earth’s crust. At the end of the Ice Ago
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