Rhomb porphyry lavas
The lava production was high when the rhomb porphyry lavas were deposited. The lavas reflect a period of abundant earthquake-related movements, when strong forces tore the crust apart.
In the Vestfold
district, one lava flow was deposited on average, every 250 000 years. Here
occurs a 3000 metre thick sequence of mainly volcanic material. In the Oslo
area, lavas were deposited on average every 800 000 years. Only a few plant
remains have been found between these lavas.
14 rombe porphyries from separat lava flows at Krokskogen west of Oslo. The flow on top left and bottom right is the oldest and youngest, respectively.
porphyry lavas are only known only from three rift areas: the East African rift
(including Mount Kilimanjaro), Mont Erebus near the Ross Sea in Antarctica and
the Oslo rift.
Geological museum, University of Oslo, Norway. Last updated 05.15.03. Trine-Lise Knudsen