Jökull - 01.01.2015, Page 40

Þorsteinsdóttir et al.
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5-4
-3,5
-3
-2,5
-2
-1,5
-1
-0,5
0
0,5
1
1,5
2
2,5
3
3,5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
M
ea
n
g
ra
in
s
iz
e
(m
m
)
M
ea
n
g
ra
in
s
iz
e
(Ф
)
Dis tanc e from s ourc e (km)
Mean grain s ize of Hekla-1947
plotted agains t dis tanc e from s ourc e
Fljótsdalsheiði
bulk
Hamragarðaheiði
bulk
Vestan Hafrafells
bulk
Bulk 3,5 km
Bulk 14 km
Bulk 32 km
Black 32 km
Brown 32 km
Bulk 48 km
Bulk 49 km
Black 49 km
Brown 49 km
Bulk 68 km
Black 68 km
Brown 68 km
Brown 74 km
Hekla-1947
16
8
4
2
1
0.5
0.25
0.125
Figure 11. Mean grain size of Hekla-1947 tephra near axis of maximum thickness plotted against distance from
source (set at Hekla top crater). Colours denote samples from locations listed to the right. – Meðalkorna-
stærð nálægt þykktarás Heklu-1947 gjósku á móti fjarlægð frá upptökum. Litaðir hringir tákna einingar og
heildarsýni Heklu-1947 gjóskulagsins á mismunandi stöðum.
0
10
20
30
40
50
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
W
ei
g
h
t
%
Dis tanc e from s ourc e (km)
F ine proportions ≤4 Φ (≤0.063 mm)
of Hekla-1947 plotted agains t dis tance from s ource
Hekla-1947 (2013)
Hekla-1947 (S Þ )
Figure 12. Weight % of fine particles in the Hekla 1947 tephra. Particles ≤4Φ (≤0.063 mm). – Þyngdarprósenta
fínefnis í Heklu-1947 gjósku. Korn ≤4 Φ (≤0.063 mm).
to source are slightly more rugged than further away
from source (Table 2). Circularity values increase
slightly with distance, the grains get more circular in
shape farther from source.
SEM-images of the Hekla-1947 tephra grains
were obtained from samples W of Hafrafell, Fljóts-
dalsheiði and Hamragarðaheiði. Four different types
of grains along with few sub-categories were noticed
40 JÖKULL No. 65, 2015