Jökull

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Jökull - 01.01.2021, Qupperneq 10

Jökull - 01.01.2021, Qupperneq 10
Larsen et al. eruption. The wind was blowing from the northwest resulting in some tephra fall in Álftaver (Jóhannsson, 1919) and about 1/2 inch (1.3 cm) in eastern Mýr- dalur (Sveinsson, 1919). In Álftaver, tephra fall re- sumed around midnight and lasted with a short pause until noon on October 23 when the total tephra fall amounted to 5 cm (Jóhannsson, 1919). The wind then shifted and carried the plume across Skaftártunga and Síða. During 5 hours of tephra fall about an inch (2.6 cm) of pumiceous ash was deposited in Skaftár- tunga (25–35 km from source). Later in the evening and the following night another inch of ash fell on Skaftártunga, bringing the total, from the beginning of the eruption, to 2.5 inches (6.5 cm). The Síða dis- trict (40–60 km from source) received less tephra fall, but the ground was covered by ash to such an extent that it prohibited grazing (Sveinsson, 1919; Jóhanns- son, 1919). In the early hours on October 24, the wind was from the northwest and tephra was carried across Álftaver and Meðalland between 4 and 6 AM. In Álftaver the accumulated tephra thickness was now 6–8 cm (Jóhannsson, 1919). This was the last sig- nificant tephra fall in these districts. From Vík vil- lage the eruption column looked as black as ever and was apparently ascending from two separated “vents”. Around 1 PM the wind had become more northerly and carried ash and pumice over Mýrdalur and Vík village (Figure 6a), causing total darkness around 2 PM. Electricity had to be turned off in the village and use of telephones was forbidden due to the threat of lightning (Sveinsson, 1919). Intense tephra fall lasted until 5 PM, when there was a short break. Less in- tense tephra fall continued until 2 AM on October 25, and had by then lasted for 13 hours (including a one hour break). After three hours of intense tephra fall the tephra thickness was 1–2 cm on level ground and after 13 hours 2–4 cm. Most of this time the darkness in Vík was so complete that windows could not be discerned from solid walls (Jóhannsson, 1919). On October 25 the wind was southerly. Minor tephra fall was reported in Skaftártunga and Síða in the morning and later that day tephra fell in Reykjavík (Figure 5) for the third time (Morgunblaðið, 26 Oct.). The next day the eruption column was described as mostly composed of steam. During the following 7 days the wind was southerly and the tephra was car- ried towards the north (Sveinsson, 1919). Tephra fall in the early hours and morning of October 26 was re- ported from Akureyri and Húsavík in North Iceland (Figure 5), in both areas footprints were traceable on the ground (Morgunblaðið, 27 and 28 Oct.; Dagur, 5 Nov.), which indicates deposition of the order of 300 g/m2 (∼0.3 mm) of tephra (Thorarinsson, 1955). Tephra fall was reported from the Skagafjörður dis- trict on October 28, (Tíminn, 14 Dec.). On October 30, with the wind blowing from the southeast, tephra fall was reported in areas to the west, in Rangárvallasýsla and Reykjavík (Morgun- blaðið, 31 Oct.; Lögrjetta 27 Nov.). During the next two days fallout was reported in northern Iceland; in Skagafjörður and Siglufjörður “the greatest” tephra fall occurred on October 31 and November 1, respec- tively (Fram, 2 Nov.; Tíminn, 14 Dec.). This was the last verified tephra fall from the Katla 1918 erup- tion (Figure 5). Re-deposition of wind-blown ash was, however, reported on several occasions during and af- ter the eruption (e.g. Sveinsson, 1919; Jóhannsson, 1919; Lögrjetta 27 Nov.). The 1918 tephra layer, preservation The 1918 Katla eruption occurred in late autumn. The tephra fall areas were grasslands and sandur plains in the lowland areas, unvegetated highland areas and ice caps. The preservation potential in the 1918 tephra fall area is therefore generally low. The Katla 1918 tephra is relatively fine grained and was mostly in the ash size range (<2 mm) out- side of the Mýrdalsjökull ice cap (Jónsdóttir, 2015). The contemporary records mention that the tephra de- posited during the first days was much finer than the tephra deposited later in the eruption. The records describe syn-and post-depositional erosion after each tephra fall event. They also describe how the tephra was eroded and redeposited by wind and water dur- ing the following winter, in some places almost com- pletely obliterated, and later on in springtime, when the ground had become snow-free, how the dry tephra was blown about “On a windy day an ash-storm blew all over the neighbourhood” (Sveinsson, 1919, 38). 8 JÖKULL No. 71, 2021
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