Náttúrufræðingurinn - 1989, Blaðsíða 48

SUMMARY
Pit craters in Iceland
by
Kristján Geirsson
Department of Geology
University of Iceland
IS-101 REYKJA VÍK
lceland
Pit craters form in some shield volca-
noes when subcircular blocks of lava fall
into channels where magma has been
drained away. They are numerous on the
island of Hawaii where they have been
most studied. The greatest number are
found in the gigantic shield volcano Ki-
lauea, including the largest pit crater Ma-
kaopuhi (Fig. 3).
Pit craters have received no attention in
geological studies in Iceland. They are
found in shield volcanoes in the active vol-
canic zone in North Iceland, from the
Kverkfjöll area to Öxarfjörður. In this ar-
ticle some pit craters are discussed and the
formation of one within the top crater of
Kollóttadyngja shield volcano (Fig. 5) is
described. It is hypothesized that at the
time when the lava lake in the top crater
was partly solidified, a swarm of wide fis-
sures on the slopes of the lava shield was
formed in a local tectonic event, draining
the top crater (Fig. 6).
On the top of an interglacial shield vol-
cano, Urðarháls, there is a 180 m deep
and 1100 m wide crater. Its form is very
similar to the pit craters of Hawaii and
Iceland, and on these grounds it is thought
to be the largest and oldest pit crater pres-
ently to be found in Iceland.
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