Náttúrufræðingurinn - 1973, Blaðsíða 43

NÁTTÚRUFRÆÐINGURINN
183
HEIMILD ARIT
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SUMMARY
The Búrfellshraun lava flow and its agc
by Guðmundur Kjartansson
The volcano Búrfell is situated 7,5 km ESE of tlie town Hafnarfjörður, SW-
Iceland. The volcano is a cinder cone rising 179 m above sea level and 80 m
above its surroundings. The crater is 140 m wide and 58 m deep. The lava
flowed mainly in the 3.5 km long lava channel, Búrfellsgjá, to the West into
the bays Hafnarfjörður and Skerjafjörður (Arnarnesvogur). The length of the
lava flow is 12 km and it covers about 18 km~, its volume being 0.3 km3.
The age of the lava has recently been determined by C14-method on a sample
lrom submarine peat underlying the lava at Balaklettur on the north shore of
Hafnaríjörður. The age is 7240 ± 130 (K—1756).
The Búrfell volcano is dissected by a minor normal fault running NE—SW.
One and a half kilometers to the west is another normal fault, Hjallar, which
runs parallel to the former one and throws the bedrock 80 m down on the
east side. This fault dissects the Búrfellshraun lava in several step-faults and
the total displacement amounts to 20 m, i. e. a movement of 2.8 mm/year.