Jökull - 01.12.1965, Blaðsíða 8

Fig. 5. Height changes o£ the firn
level along the section Depill-Gríðar-
horn 1960—1966. — Breytingar á yfir-
borði Grímsvatnasléttunnar milli Depils
og Gríðarhorns 1960—1966.
ice was found to be 665 m, but the measure-
ment is classified by Holtzscherer as “peu sur”.
At the westernmost point, situated about 1 km
N of the caldera wall near Svíahnúkur vestri
the thickness was found to be 580 m and the
measurement is classified as “bon” (Holtzscher-
er, op. cit., pp. 21 and 22—24). No water was
detected beneath the ice. About 6 km SE of
Svíahnúkur eystri the ice thickness was found to
be 1060 m, the greatest thickness measured on
Vatnajökull.
A new effort to measure the thickness of the
ice in the Grímsvötn area was made by a Grims-
vötn expedition in June 1955. The seismic
soundings were also this time carried out by
a French geophysicist, fean Martin, like Joset
a member of P. E. Victors Expeditions Polaires
Fran^aises. Martin was assisted by the Icelandic
physicist Ari Brynjólfsson and the present
writer and driver of the wiesel used was Olafur
Nielsen. (Thorarinsson 1955). The points where
thickness was measured are numbered with
Roman figures on the map Fig. 7 and the re-
sults are listed in Table II.
Like Joset, Martin failed in obtaining reli-
able reflections in the area NE of Svíahnúkur
eystri. But the results of most of the soundings
within the caldera are characterized by Holtz-
scherer as “good” or Sfair” ancl they are in
good agreement with Joset’s—Holtzscherer’s
Fig. 6. Even short after
a jökulhlaup the central
area of Grímsvötn caldera
is practically flat. — Jafn-
vel rélt eftir jökulhlaup
er yfirborð miðsvœðis
Grímsvatnsléttunnar nœr
marflatt.
Photo S. Thorarinsson.
June 1955.
114 JÖKULL