Jökull - 01.12.1977, Blaðsíða 43

Fig. 21. The Selsund
Pumice in the bed of a
former lake SW of the
Selsund farm (cf. Fig. 20).
Mynd 21. Selsundsvikur-
inn í fornu vatnsstœði
SA af Selsundi.
Photo S. Thorarinsson.
gtained and thin, yet showing the distinct
colour changes characteristic of H4 and H:l. The
volume is not known, but it is certainly much
less than the volume of the other four acid
Hekla layers.
is poorly stratified and coarse-grained.
1 he distinct colour changes and abundant
Hthics are the most promincnt features. Maxi-
mum thickness in the Hekla area is more than
3 m.
H5 is well stratified with alternating layers
of extremely fine-grained ash and coarse pumice.
The fine-grained layers resemble sub-unit (a) in
H4. The fine-grained ash spreads easily and
tliis may explain why H5, in spite of its smaller
volume, covers about the same area as H4 and
TABLE II
Age, area, volume and SiOo content of Hekla’s acid tephra layers
QJ PQ <D bD 03 ð Probable corrected age B.P. (1950) Area on land within 0.1 cnt isopach, km2 Calculated volurne as freshly fallen on land, km3 Estimated volume as freshly fallen on land and sea, km3 Ibid. calculated as dense rock km3 % SiOo of initial tephra
Hi 846 55.000 1.4 2.0 0.5 70
h3 ~ 2.800 ~ 2.900 80.000 8.0 12.0 2.2 73
Sp*) ~ 3.500 > 10.000 0.2 <0.5 <0.1 ~ 70
h4 ~ 4.000 ~ 4.500 78.000 6.7 9.0 1.8 74
h5 ~ 6.200 ~ 7.000 62.000 2.5 ~ 3.0 0.7 74
) Sp = Selsund pumice.
JÖKULL 27. ÁR 41