Jökull - 01.12.1974, Page 56

* Stratigraphic position
of dated sample
• Conglomerote horizon
— Tillite horizon
+ +• Tillite horizon associated
with hyaloclastiles.
Extensive hyaloclastites are
indicated by double crosses
I Acid volcanism
Fig. 8. The Húsafell sec-
tion fitted to the geo-
polarity time scale on the
basis of K/Ar datings
and paleomagnetic strati-
graphy. The geopolarity
time scale is after Cox
(1969) and McDougall
and Aziz-Ur-Rahman
(1972). The stratigraphic
position of glacial hori-
zons is indicated by bars.
Crossed bars indicate that
hyaloclastites are associat-
ed with the tillites. Con-
glomerate horizons below
the Mammoth event are
indicated by dots.
Mynd 8. Jarðlagasnið af
Húsafellssvœðina (vinstri
hlið) fellt að segultima-
talinu (hcegri hlið) á
grundvelli K/Ar aldurs-
greininga og segulmcel-
inga. Af samanburðinum
má sjá tímasetningu
hinna þriggja líparítgos-
hrina og dreifingu jökul-
skeiðanna í tíma. A jarð-
lagasniðinu samsvara 3,5
mm 100 m þykkum jarð-
lagabunka.
4. DEVELOPMENT OF THE LAVA PILE
IN THE LIGHT OF THE FIXED AGES
The fixed age of the sequence allows a
number of conclusions to be made regarding
the development of the lava pile. The most
important of these concern (1) the rate of
growth of the lava pile (2) the life span of the
central volcano (3) the onset, frequency and
duration of glaciations and (4) the significance
of the unconformities in tlre upper part of tlie
section.
4.1 RATE OF LAVA PRODUCTION
The rate of lava production can be estimated
with some confidence for several successive time
intervals as is summarized in Table 2.
Values for the thickness and number of flows
are derived from the area on the soutlrwestern
outskirts of the central volcano and just to the
west of it. Tlie average rate of growth of the
lava pile is very near to 110 m per 100,000
years. The number of flows within a group
shows less obvious relationships to the time in-
54 JÖKULL 24. ÁR