Jökull


Jökull - 01.12.1977, Síða 12

Jökull - 01.12.1977, Síða 12
too, that basaltic activity was directly associated with tlie eruption (Sparlts et al. 1977), as borne out by a basaltic tephra layer in the Bárdar- bunga core. The íollowing quotation is from Thorarins- son’s (1963) book on Askja “On Jan. 3 1875 a fiery column rising in the south was seen from the Mývatn region; clouds of srnoke had been observed earlier. About the middle of February an expedition of farmers from around Lake Mývatn set out for Dyngju- fjöll. When it reached Askja on February 16, huge solfataras were active in the south-east corner of the depression, “flinging rocks and mud several hundred feet into the air”. The report of the expedition does not indicate tliat any volcanic eruption occurred during their stay in Askja, nor does it appear to warrant the conclusion (which some have, nevertheless, drawn from it) that there was freshly poured- out lava anywhere around. Water was flowing from the solfataras, and what seems to be generally indicated is an overture to an erup- tion very similar to that which preceded the eruption of 1961, except that the activity ap- pears to liave been rather more violent; very likely some sort of explosive eruption had taken place.” Thorarinsson (op. prox. cit.) states further that apparently several centuries preceding the 1875 eruption “constituted an intermission in Askja’s activity. But then Dyngjufjöll were an unexplored region practically up to the year 1874. The smoke that was sometimes seen rising above Dyngjufjöll strengthened the popular be- lief in the existence of outlaws in the highlands. .... Tlie first person known to have visited Askja was the surveyor Björn Gunnlaugsson, who came there in 1838, but could see only little because of fog”. Another inaccessable and little-explored vol- canic area is tlie DYNGJUHÁLS region, 30 to 40 km north of thc Bárdarbunga site. According to Jónsson (1945) several fresh-looking lava flows in this region attest to vigorous activity in recent centuries. However, the only eruption that Jónsson (1945) attributes with certainty to this region, that of 1862—64, has now been shown to have taken place in Tröllahraun, west of Vatnajökull (Thorarinsson & Sigvaldason 1 0 JÖKULL 27. ÁR 1972). Another type of possible indicators of eruptions on Dyngjuháls, where 7 crater rows extend beneath the glacier Dyngjujökull, could be the floods in Jökulsá between 1655 and 1729. But, as already indicated, it seems most reason- able to attribute them to volcanic activity in Kverkfjöll. Tlierefore, as matters now stand, it appears that the activity in Dyngjuháls may be considerably older than hitherto supposed. ÞÓRDARHYRNA, within the Vatnajökull ice cap some 40 km SW of Grímsvötn, erupted in 1903, and probably in 1823 (Thorarinsson 1974) . Tephra from the 1903 eruption was col- lected aboard a ship off Langanes (NE Iceland) and analyzed by Alouritzen and Noe-Nygaard (1950. Table II, nr. 6). Other active volcanoes may exist beneath tlie Vatnajökull ice sheet, as indicated by hydro- thermal activity and periodic jökulhlaups issu- ing from underneath the ice sheet. Two such places have especially been suggested as vol- canoes, “Sigin” (the cauldrons) NW of Gríms- vötn, from which issue floods in Skaftá, charged witli hydrogen sulphide and other fumes, and another location NE of Pálsfjall, where depres- sions in the glacier attest to thermal activity underneath. The latter place may have been the site of an eruption in 1753 (Thorarinsson 1974, pp. 57—58). However, next to nothing is so far known of tlieir volcanic liistories. ÖRÆFAJÖKULL, 25 km SE of Bárdarbunga, erupted in 1727 and 1362 (Thorarinsson 1958). Öræfajökull is a typical central volcano, with a caldera at the summit. Its products in these two eruptions have been silicic to intermediate in composition (Table II, no. 11). Finally, HEKLA and KATLA, both some 130 km to the south-west of Bárdarbunga, have erupted many times during the last centuries. The volcanic history of Hekla in particular is well known due to the researches of Thorarins- son (1967), and recent studies have cast much light on that of Ivatla as well (Thorarinsson 1975) . As seen from this list, only a fraction of the tephras in the Bárdarbunga core could be ex- pected to be from known eruptions, having a
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