measurements have been carried out on a regular basis in Surtsey in
order to observe the effects that heat has on the consolidation of tephra
and to determine at what temperatures the various secondary minerals
form, both in tephra and in lava. The lava has partly conserved its
heat, especially at the western crater. In the summer of 1986 the gas
temperature was still around 300°C at the western crater, but it
has cooled rapidly since then.
In April 1968, anomalous temperatures
were observed in the tephra, and the measurements from November 1969
indicated that a mild hydrothermal area had formed at the center of
the island. The temperature above sea level has risen to a maximum of
100°C (steam temperature) in the tephra layers. Since 1972 the temperature
has been slowly dropping. In 1979 an experimental hole was drilled to
a depth of 180 m on the eastern part of the island. Since 1980, the
mean temperature decrease in the drillhole has been about 1°C annually.
The measurements from 1980 and 2002 are shown on this
graph for comparison. In the summer of 2002 a small pool with 78°C
water was discovered at sea level just beneath the westernmost cliffs.
hydrothermal area in Surtsey is obviously connected to the lava crater
and its feeder dikes. It is most likely that intrusions formed in the
period from December 1966 to January 1967 are the cause of the hydrothermal
activity. The sea water seems to have an open pathway through course
strata of rocks at the base of the island. When the ocean makes contact
with the hot core, it warms up and the hot water evaporates. The ocean
seems to be boiling in some places at sea level, and the steam travels
easily through the tephra and lava.
P. Jakobsson – email@example.com)