Rit (Vísindafélag Íslendinga) - 01.06.1967, Qupperneq 192

188
— 1967: The eruptions of Hekla in historical times. The Eruption of
Hekla 1947-1948, I: 1-170.
Tryggvason, T. 1965: Petrographic studies on the eruption product of
Hekla 1947-1948. The Eruption of Hekla 1947-1948 IV. 6, 13 pp.
Macdonald and Katsura 1964: Chemical composition of Hawaiian lavas.
Joumal of Petrology 5, 82—133.
DISCUSSION
H. Sigurdsson: The composition gap of Hekla’s lavas is ex-
tremely interesting. Is it certain that the lavas with 45—46%
Si02 are from Hekla itself hut not from fissures in the neigh-
bourhood? Also, do you expect that the compositional gap
will be filled by further work?
/. Tómasson: The composition gap might be narrowed
through further investigation but my petrographical research
points to the fact that it is a real gap. Doubtless some of the
lavas with silica content 45—46% are from the Hekla pro-
per but the same type is also erupted from the fissures pa-
rallel to Hekla.
G. Pálmason: Would you venture a guess as to the pro-
bability of a sialic layer under Hekla?
/. Tómasson: Yes, this is the easiest way of explaining the
chemical composition of Hekla’s volcanic products, although
the chemical composition of this sial is a little obscure.
Trausti Einarsson: Between eruptions, in less than 100
years, the top of the “dormant” magma mass changes. This
suggests gravitative differentiation but does it fit well with
assimilation?
/. Tómasson: The typical Hekla magma appears to be
created by assimilation, but I agree that during the dormant
periods gravitative differentiation takes place.
Trausti Einarsson: Remelting of acid rocks?
/. Tómasson: Yes.
Trausti Einarsson: I wonder what is the ratio between the
total of produced magma and the volume of the reservoir,