Jökull - 01.12.1952, Page 17

layers were separated from the first ash by clay
bands.
Identification of the volcanic ashes was made
by determination of colour, refractive index (in
sodium light), and by measurement of grain
size. Thorarinsson also used silica content as
a feature in identification, but this was not
possible here, owing to the prohibitive cost of
analysis. However, Thorarinsson stated that
identification was usually possible without the
use of silica content.
The results obtained were sufficient to iden-
tify the three ashes with three of the Hagavatn
soil profile. (The data obtained concerning the
various ash analyses are present in detail in
Thorarinsson’s „Tefrokronologiska studier pá
Island”, 1944).
The data obtained were as follows: —
Ash
No. Particle diameter.
T >2.0 mm.
2 Very fine. < 0.2 mm.
3 > 2.0 mm.
Refractive
Index.
1.606
1.608
1.618
1.619
1.555
1.557
Colour.
Black
Black
Black
The ashes 1, 2 and 3, are identified with
ashes Nos. III, IV and V of the soil profile
measured by Thorarinsson below Leynifoss
(cf. Fig. 1). These ashes were from the erupt-
ions of Hekla 1693, Katla 1721, and Hekla 1766,
respectively.
An examination of the glacial materials along
tlie moraines forming the southern shore of the
present lake, showed that there was much var-
ved sediment present. This had been thrust up
from the bed of the lake during an advance of
the ice. Among these disturbed sediments was a
section which contained a rhyolitic and a basic
ash, both within the thickness of a single varve.
The sediments in which this ash was found
approached closer to the true varve, and showed
a gradation between winter and summer clays,
with no minor laminations as were found in the
clays of the western basin.
The complete section containing these ashes
was as follow:
Fig.5. Part of the gully section near the southern
margin of the lake bed. Note thicker sand
intercalating between winter layers, showing
slumped bedding effects.
Hvörf í botnseti nœrri suðurströnd Hagavatns
(þeim hluta, sem nú er þurr.)
One varve
2i/2"
(6.2 crn)
Grey (laminated) clays.
' Yellow-fawn clay.
Dark grey ash, slightly
decomposed. c.
Grey clay. Dark brown ash b.
Grey clay. Grey laminated clay. White volcanic ash. a.
Fawn clay.
No. Particle Refractive
Ash diameter Index. Colour.
c. 0.2 mm. diameter 1.598 Dark grey (originally
b. 0.2 mm. diameter f 1.589 black). Dark
J 1.499 brown.
a. 0.2—2.0 mm. diam. 1.498 White.
The layer „c“ can be identified with layer
Vlla, and the layer „a“ with Vllb. These are
two ashes of a profile characteristic over much
of South Iceland, which was pre-colonization in
age. It can also be noted that both eruptions
occurred in the same year, the basic layer being