Jökull - 01.01.2021, Page 16

Larsen et al.
Figure 10. a) Jökulhlaup deposits on the upper part of Mýrdalssandur, north of Selfjall and Léreftshöfuð. Photo
taken sometime between October 16 and 19, 1918. Vatnsrásarhöfuð hill at upper left, Kötlujökull black with
ash upper middle, Kurl (cone shaped hill) and Hafursey at upper right. The photo was taken from Léreftshö-
fuð looking NNE. Huge icebergs and thick sediments have piled up in front of Léreftshöfuð and Selfjall, now
breached by the Múlakvísl river that flows towards the viewer. Much more water follows the main flood route
closer to Hafursey. Photo Þorlákur Sverrisson. – Jakahrannir og setbunkar á efri hluta Mýrdalssands, norðan
Selfjalls og Léreftshöfuðs. a) Ljósmynd Þorláks Sverrissonar, ódagsett en vafalítið tekin milli 16. og 19. október
1918. Vatnsrásarhöfuð er ofarlega til vinstri, Kötlujökull svartur af ösku fyrir miðju, Kurl (topplaga hæð) og
Hafursey til hægri. Allmikið vatn er enn á sandinum, mest í farvegi meginhlaupsins næst Hafursey en Múlakvísl
hefur grafið sér leið gegn um hrönnina og rennur í átt til ljósmyndara.
tial flood removed some of the new guide posts along
the path that had been marked across Mýrdalssandur
after the eruption (Sveinsson 1919).
Enormous heaps of ice and sediments had been
left on the Mýrdalssandur plain, in particular on its
upper part (Figure 10a and b) and remained there for
months. On the lower part of the sandur the flood had
cleaned the ice from the channels, leaving bars stud-
ded with ice in between. These bars, with pockets left
by melted ice blocks (Figure 11), were visible until
the sandur was revegetated.
The 1918 jökulhlaup extended the shoreline tem-
porally up to 4 km beyond the 1904 shoreline
(Jóhannsson 1919) and raised the surface of the san-
dur deposit by 5–10 m locally (Gudmundsson et al.,
2018).
SOME REFLECTIONS ON THE 1918
KATLA ERUPTION AND THE
JÖKULHLAUP
The contemporary descriptions of the 1918 Katla
eruption contain much greater detail than could be in-
cluded in this paper. Frequent changes in direction
and strength of the wind resulted in rather compli-
cated tephra dispersal, as evidenced by the isopach
map. Photographs taken during the eruption allow es-
timates of the plume height at the time of photography
and a better location of the source vents (Larsen and
Högnadóttir, this issue). Measurements of the tephra
layer within the Mýrdalsjökull ice cap provide a new,
previously unused data set (Gudmundsson et al., this
issue). These papers should be regarded as steps in
deciphering the details of the 1918 Katla eruption.
14 JÖKULL No. 71, 2021