Náttúrufræðingurinn - 1990, Síða 50

SUMMARY
Postglacial lavas
on Hagafell,
Central Iceland.
by
Jón Viðar Sigurðsson
Science lnstitute
University of Iceland
Dunhaga 3
1S-107, REYKJAVÍK
Iceland
The tablemountain Hagafell is located
in the southern part of Langjökull glacier
in central Iceland. Postglacial lavas have
been found in the northern part of this
flat-topped mountain at a height of 900 m
a.s.l. The youngest lava flow has been
named Svartahraun as it is characterized
by a dark appearance. The flow was very
small, 2.4 km2 and 7,400,000 m3. The cra-
ters lie in a row in the northernmost part
of Hagafell. Other older postglacial lavas
lie under and around Svartahraun and are
different in that they look fresher as
Svartahraun has suffered from severe frost
weathering. All the lava flows are com-
posed of olivine tholeiites, which is the
dominant rock type of the Langjökull ar-
ea. In one place xenoliths were spotted
that have a rim of plagioclase and olivine
crystals and glass cores with the same
chemical composition as the lavas. The
xenoliths may have been formed when py-
roclastic fragments from the craters fell on
and penetrated the flowing lava.
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