Jökull - 01.06.2000, Page 8

Eysteinn Tryggvason
Figure 3. Observed ground tilt at two optical levelling tilt stations, Kötlukriki and Jökulkvísl, near the eastern
extremities of the glacier Mýrdalsjökull. Error bars show one standard error of tilt computed for the period from
íirst observation to each succeeding observation. Horizontal scale is time from beginning of the year 1965 to
end of the year 1995. Vertical scale is either east- or north-component of ground tilt in microradians, positive
if uplift is towards east or north. - Mœldar hallabreytingar við austurjaðar Mýrdalsjökuls, í Kötlukrika og við
Jökulkvísl. Fyrsta mœling var gerð árið 1967. Lóðrétti ásinn sýnir hallabreytingu til austurs (efri hlutinn) og
norðurs (neðri hlutinn) á árunum 1967-1995.
field is about 15 cm, and that the thickness of the el-
astic lithosphere is 5 to 10 km.
Suggested tilt up towards west or north-west at the
station Kötlukriki between 1967-1973 and 1986-1995
(Figure 3) is possibly the result of less average glacier
load during the latter period.
CONCLUSIONS
Observations of ground tilt at the edge of the Mýr-
dalsjökull glacier from 1967 to 1995 suggest that
annual variations in the glacier load causes measura-
ble ground tilt. There is no clear evidence that sub-
surface magma movement at Katla has caused any
ground deformation during this period. There is a
vague indication of secular tilt, up towards west or
north-west, at the station Kötluki'iki, and observati-
ons at the station Jökulkvísl do not contradict such
secular tilt. The suggested tilt rate is 0.1 /rrad per
year at Kötlukriki, and less at Jökulkvísl. This tilt
rate is too small to be observed with confidence and
can be caused by less average glacier load during the
observations of 1986-1994 than during the observati-
ons of 1967-1973.
Considering the rate of secular tilt of 0.1 /irad per
year at Kötlukriki to be real, and assuming that this tilt
is caused by increase of pressure in a magma cham-
ber at 5 km depth below Katla, then a ground uplift
of about 0.6 mm per year is suggested. To cause this
much uplift, about one million cubic meters of magma
6 JÖKULL No. 48