Náttúrufræðingurinn - 1968, Síða 110

218
NÁTTÚRUFRÆÐINGURINN
mantle of tuff. These necks lie on a 600 m long N-S- striking line in the
eastern part of Dyrhólaey. After a period of quiescence a renewed submarine
volcanic activity started on a 1500 m long N-S- striking fissure in the western
Dyrhólaey approximately 1600 in to the west of the earlier one. The first
phase of this eruption was an outpouring of pillow lava, wliich now is confined
to the lowermost part of the southwest cliffs of the headland. Then a change
in the mechanism of eruption took place and explosive activity set in. At the
same time the activity was confined on 3 or 4 vents on the fissure. During this
phase the eruption produced mainly tuff and breccias, which were piled up to
an altitude of approximately 150 m. When the volcano had reached this height
again a change occured in tlie type of eruption, and the northernmost vent
began to produce lava, which covered the east flank of the volcano. Below
the east flank of the volcano the lava covered beach deposits, derived from
the tuff rims, and flowed then into the sea where it first formed a foreset beclded
pillow breccia, which is now exposed under the lava flows.
The geological structure of Dyrhólaey is in many respects similar to that of
Surtsey, the only difference is that in the former the socle is better exposed.
The Dyrhólaey eruptions seem to liave occurred during an interglacial,
probably the last or second last, when the sea level at the time of the eruption
was sliglitly higher than the present sea level. Its interglacial age is also ve-
rified by intensive glacial erosion.
LEIÐRÉTTING
í grein um ritstjóraskipti í síðasta hefti Náttúrufræðingsins var
m. a. rætt um gjöf Eyþórs Erlendssonar á litmyndum í tímaritið.
Af orðalagi greinarinnar mátti skilja, að hér væri aðeins um eina
mynd að ræða. Svo er þó ekki. Eyþór hefur gelið 3 litmyndir og
skal ein birtast í hverjum árgangi 1967—69, en verðtnæti myndanna
allra skiptir tugum þúsunda króna.
Lesendur og gefandi eru beðnir velvirðingar á þessum leiðu
mistökum. Ritstj.