Jökull - 01.12.1978, Blaðsíða 111

of ice advance in Melasveit, are thought to
represent the Upper- and Lower Dryas.
ON THE FORMATION OF
“RAUDIMELUR” ON THE REYKJANES
PENINSULA
Freysteinn Sigurdsson, National Energy Aut.hority,
Sigurdur G. Tómasson, National Energy Authority
In the hydrogeological survey for the Sud-
urnes Regional Heating Service (Hitaveita
Suðurnesja) some observations were made at
Raudimelur — an uplifted bar, now situated
10 km inland and surrounded and partly
flooded by recent lavas — because of possible
pollution from gravel mining and other work
in progress there. The bar is approximately
5—20 m thick, rests on striated interglacial
lava and reaches 30 m height above present
sea level. The formation can be divided into
five stratigraphical units numbered upwards:
1. Striated interglacial lava, forming the base.
2. Sand and gravel, often cross bedded, pos-
sibly outwash from the nearby Stapafell, a
subglacial volcano.
3. Tillite and lava, both striated.
4. Gravel of uncertain place of origin.
5. Coarse gravel or boulder bed, possibly
originated in the recent Lágafell shield
volcano.
On the basis of the section and its connec-
tion with volcanic formations on the penin-
sula it is suggested that the age of the Raudi-
melur bar is pleistocene (1—4)/holocene (5).
In addition to the evidence of Raudimelur,
observations were made on littoral deposits on
recent lavas at 8—10 m height above the
present sea level and a model constructed of
the fluctuation of the sea level which indicates
a regional postglacial transgression.
SOME GEODETIC OBSERVATIONS IN
CONNECTION WITH THE KRAFLA
RIFTING EPISODE IN 1975-1977
Oddur Sigurdsson,
National Energy Authority
A 5 km long line within the graben, formed
in Dec. 1975 in the Axarfjördur area 40 km
north of the Krafla caldera, showed signifi-
cant changes from 1962 to 1976. The wes-
ternmost 1 km is inclined 103 uradians to the
east, the next 4 km have a more gentle dip in
various directions. Other parts of the graben
had no remeasurable points or bench marks. A
line of bench marks running obliquely to the
Krafla fissure swarm and touching it at the
coast in Axarfjördur, shows a 60 cm greater
uplift close to the northern end than the
southernmost part. At the southern end of this
line there are several precision levelling profi-
les, that show changes of about 3 uradians to
the SSW between the years 1974 and 1976, the
profiles being practically undistrubed 1971 to
1974. A net of 14 stations, determining the
relation between the level of lake Mývatn and
the bedrock, show more than 30 cm relative
uplift in the easternmost part during 1977,
mainly in two episodes, namely April 27 and
Sept. 8 coinciding with small eruptions and
earthquake swarms.
A NEW TILTMETER
Sigurjón Sindrason and Halldór Ólafsson, Nordic
Volcanological Institute
Tilt variations down to 10-7 rad. can be
detected with a new tiltmeter designed at the
Nordic Volcanological Institute following
suggestions from Ævar Jóhannesson.
The sensors are 4 magnetic field sensitive
resistors. These detect movements of a magnet
suspended in a pendulum 0.5 mm over the
resistors.
The prototype was installed in the Krafla
JÖKULL 28. ÁR 109