Náttúrufræðingurinn - 1990, Side 19

3. mynd. Lausagrjót innlind-
að í hraunstorku. Loose gra-
vel included in lava. Ljósm.
photo Jón Jónsson.
Jón Jónsson 1987. Eldgjárgos og Land-
brotshraun. Náttúrufrœðingurinn 57. 1-
20.
SUMMARY
An unusual occurrence in
a pseudocrater
by
Jón Jónsson
Smáraflöt 42
IS-210 GARÐABÆR
Iceland
Amog the numerous pseudocraters in
the Landbrot district South Iceland there
is one named Söðulhóll, which has now
been excavated for construction material.
The excavation has exposed a section with
two horizons of sandy soil which evidently
originated underneath the lava flow. The
lava came from an eruption that occurred
ca. 7000 years ago. These pseudocraters
were formed when hot lava (ca. 1000°C.)
flowed over a waterlogged area that was
at least partly covered by vegetation.
The wet soil, together with the volcanic
material, was carried to the surface in
the explosion and precipitated with it. The
resulting layers contain remains of vegeta-
tion and a large number of fresh water
diatoms.
73