Rit (Vísindafélag Íslendinga) - 01.06.1984, Side 344

VÍSINDAFÉLAG ÍSLENDINGA
(SOCIETAS SCIENTIARUM ISLANDICA)
THE ERUPTION OF
HEKLA 1947-1948
I. S. Thorarinsson: The Eruption of Hekla in
Historical Times. A Tephrochronological
Study. Appendix by J. Tómasson: Minera-
logical and Petrographical Characteristics of
Icelandic Tephra. Rvk. 1967.
II. 1. S. Thorarinsson: The Approach and Beginn-
ing of the Hekla Eruption. Eyewitness Ac-
counts. Rvk. 1950.
II.2. Tr. Einarsson: A Study of the Earliest Photo-
graphs of the Eruption. Rvk. 1950.
II. 3 S. Thorarinsson: The Tephra-fall from Hekla
on March 19th 1947. Rvk. 1954.
II.4. G. Kjartansson: Water Flood and Mud
Flows. Rvk. 1951.
III. 1. G. Kjartansson: Some Secondary Eífects of
the Hekla Eruption. Appendix by G. Thor-
kelsson: Chemical Analyses. Rvk. 1957.
111.2. K. Stefánsson & J. Sigurjónsson: Tempor-
ary Increase in Fluorine Content of Water
following the Eruption. Appendix by G.
Thorkelsson: Some Reflections on Fluorides
of the Ash and Water during the Eruption.
Rvk. 1957.
111.3. B. Sigurdsson & P. A. Pálsson: Fluorosis of
Farm Animals during the Hekla Eruption of
1947-1948. Rvk. 1957.
IV. 1. S. Thorarinsson: Course of Events. Appendix
I by E. Tryggvason: Earthquakes during the
1947—48 Hekla Eruption. Appendix II by B.
Líndal & Th. Sigurgeirsson: Temperature
and Chemical Composition of Emanations
from the Hekla Volcano after the 1947—1948
Eruption. Rvk. 1976.
IV.2. Tr. Einarsson rate of Production of Material
during the Eruption. Rvk. 1949.
IV.3. Tr. Einarsson: The Flowing Lava. Studies of
its Main Physical and Chemical Properties.
Rvk. 1949.
IV.4. Tr. Einarsson: Chemical Analyses and Differ-
entiation of Hekla’s Magma. Rvk. 1950.
IV.5. Tr. Einarsson: The Basic Mechanism of
Volcanic Eruption and the Ultimate Causes of
Volcanism. Rvk. 1950.
IV.6. T. Tryggvason: Petrographic Studies on the
Eruption Products of Hekla 1947—1948. Rvk.
1965.
V.l. G. E. Sigvaldason: The Petrology of Hekla
and Origin of Silicic Rocks in Iceland. Rvk.
1974.
V.2. Tr. Einarsson: Studies of the Mechanism of
Explosive Activity in the Hekla Eruption.
Rvk. 1951.
PÁLLIMSLAND
Nordic Volcanological Institute,
University of Iceland

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The magma system of Jan Mayen produces an alka-
line rock suite, ranging in composition from ankaramites
to trachytes and containing coarse-grained xenoliths ran-
ging from wehrlite to syenite. The mineralogy of the
xenoliths is reflected in the phenocryst phases of the
lavas. A pattern is present in the distribution of the rock
types on the island.
The volcanism on Jan Mayen is the result of the
drifting of a crustal segment of relatively evolved com-
position and low melting point into a higt geothermal
gradient which extends from the Mohns Ridge across the
Jan Mayen Fracture Zone and into the Jan Mayen
Ridge-Iceland Plateau block of the Eurasian Plate. This
crustal segment gained a highly evolved composition
during the Greenland-Norway continental break-up and
later the Kolbeinsey Ridge Rift Zone formation in the
same region, —60 and 30 million years ago respectively.
The compositional spectrum of the rock suite is the
result of the production of three different primary mag-
mas in the magma system. These evolve to a different
degree through crystal fractionation and the products
mix in varying proportions to produce the different rock
types and their distribution pattern.
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