Jökull - 01.12.1983, Síða 110

maximum extent of glaciation in North-West Ice-
land. It is not unlikely that the Skagi lake was
formed at the ice-lake stage in F njóskadalur and it is
tentatively suggested, that the age of the Skagafjall
deposits is 17,000-20,000 B.P.
The provenance of the tephra is from one of the
volcanic systems which are still active or dormant in
Iceland. In postglacial time four volcanoes, Hekla,
Askja, Oræfajökull and Snæfellsjökull are responsi-
ble for most of the acid explosive eruptions (Thorar-
insson 1958). Askja belongs to the tholeiitic series,
Hekla and Oræfajökull to the transitional alkalic
series and Snæfellsjökull to the alkalic seríes(Jakobs-
son 1979). The Skagafjall tephra is tholeiitic in com-
position and most likely originated from Askja or
the Dyngjufjöll area.
Hammer (1980) has shown that most, if not all
violent eruptions that have occurred in the North-
ern Hemisphere in the last 10,000 years can be
detected in cores from the Greenland ice. It is then
possible that aerosols from the eruption, which
produced the Skagafjall tephra, can be detected in
the Greenland ice and then dated exactly.
ACKNOWLEDGEMENTS
The Jield work was mostly carried out in August 1979
and June 1980, and was financed by the author. The field-
work was used as a basis for a 4th year’s thesis at the
University of Iceland (Sigurvinsson 1982). Supervisor dur-
ing fieldwork and preparation of the thesis was Dr. Jón
Eiríksson and I am grateful lo himfor valuable discussions,
assistance and also for reading the manuscript and improv-
ing the English text. Thanks are also due to Professor
Thorleifur Einarsson for his advice and commenls. My
thanks are also due to Dr. Sigurður Steinthorsson for the
chemical analysis. I am also grateful to all others who have
contributed to the work by inspiring discussion.
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108 JÖKULL 33. ÁR