Náttúrufræðingurinn - 1977, Blaðsíða 24

S U M M A R Y
Rifting and volcanism in the Kralla area 1975—1977
by Dr. Axel Björnsson,
National Energy Authority, Dept. of Natural Heat,
Laugavegur 116, Reykjavili, Iceland
Tlie Mid-Atlantic Ridge is the plate
boundary between the American and
European plates. Its manifestation in Ice-
land is the Neovolcanic zone. In north
Iceland the activity of tliis zone of spread-
ing and active volcanism is confined to
several fissure and fault swarms (Fig. 1).
In one of these fissure swarms, the Krafla-
swarm, a rifting episode started on 20th
December 1975 with a basaltic eruption
and an exceptionally intense earthquake
swarm. The center of this swarm runs
through the central volcano Krafla north-
east of the lake Mývatn (Fig. 2).
The seismic activity culminated in
January 1976 but gradually decreased un-
til March. Since then there has been a
significant interplay between land eleva-
tion changes, fault movements and earth-
quake activity within the Krafla caldera
and the associated fault swarm (Fig. 6).
The inflation is interpreted as caused by
f low of magma lrom below into a magma
chamber in the Krafla caldera. The de-
ílation events are caused by release of
pressure in tlie magma chamber by wid-
ening of the rifts north and south of the
caldera and flow of magma into the fis-
sures of the fault swarm (Fig. 7). Associ-
ated with the flow of magma into the
fault swarm new fumaroles liave been ob-
servecl to the north and south of the
caldera. Relative drift of the two plates
has been found, by direct measurements,
to be more than 2 metres.
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