Náttúrufræðingurinn - 1975, Blaðsíða 67

N ÁTTÚ RU FRÆÐINGURINN
57
HEIMILDARIT
Askelsson, Jóhannes, 1960: Fossiliferous Xenoliths in the Móberg Formation
o£ Soutli Ieeland. Acta Nat. Isl. II, 3.
Einarsson, E.H. 1962: Fornskeljar í móbergi í Höfðabrekkuheiði. Náttúrufr.
32:35-45.
— 1967: Steingervingar í Skammadalskömbum. Náttúrufr. 37: 93—104.
S U M M A R Y
NaCI — scaling and the origin of palagonite in Mýrdalur
by
Einar H. Einarsson, Skammadalshóll, Mýrdalur
In dry and hot weather a gray and sometimes nearly white scaling forms on
many palagonite cliffs in Mýrdalur. This scaling is composed of small grains
o£ salt, mostly NaCl. Although the scaling does follow certain horizons in the
palagonite, these dilfer from place to place. It is never found evenly distributed
over large areas, but rather occurs in small patches here and there. The scaling
is sometimes found near and within crewasses in the formation but this is
rather rare. The most common occurrence is in solid thick formations, where
the rock is not fractured and forms steep cliffs.
The author has oljserved such scaling at Hjörleifshöfdi, Háfell, Höfda-
brekkuhamrar, Fagradalshamrar, Víkurhamrar, in Hnjúkur (western half of
Reynisfjall), Dyrliólaey, Pétursey and Klifandagil in Mýrdalur and in eastern
Drangshlídarfjall and Hrútafell in the Eyjafjöll district.
The salt appears to be dissolved from the palagonite formation and not due
to salt spray froni ocean surf as one might at first suggest. The scaling is thus
interpreted as an indicator of submarine origin of the palagonite formations,
the salt being mixed with the tephra when sea water flowed into the crater
between phreatic explosions. The salty mixture is then thrown out of the
crater and distributed over the hyaloclastites as far as the explosions can
reach.
This conclusion is supported by the evidence of xenoliths of marine sedi-
ments thrown up in eruptions of Pétursey, Heidarbrún south of Skammdals-
heidi and Núpar in Höfdabrekkuheidi.