Jökull


Jökull - 01.12.1956, Page 6

Jökull - 01.12.1956, Page 6
on the whole been receding since ab. 1870, although the recession has now and then been interrupted by stagnation and minor advances. According to Eythórsson (1949, p. 251), the front of Svínafellsjökull was as a whole very near the same in 1932 as in 1904. The variations of the glaciers until 1932 may by summed up as follows: Beginning of 18th century: Glaciers consider- ably larger than in 1935. 1740’s: Glaciers larger than in 1935. Years or decades immediately preceding 1794: Advance. 1794: Glaciers larger than in 1935. 1830’s: Probably advance. 1865: Svínafellsjökull probably as large as in 1904. 1932: Svínafellsjökull about the same as in 1904. The variations since 1932 are, according to Eythórsson measurements (1949, p. 251, 1951, p. 16, 1952, p. 31, 1953, p. 49, 1954, p. 46, 1955, p. 40; Mercanton 1952, p. 117) as follows: Skaftaf.jök. Svinaf.jök. Svínaf.jök. ■ (N) (S) 1932-34 + 60 — 65 — 33 1934-35 - 45 — 15 — 20 1935-36 -155 0 — 10 1936-37 - 71 + 3 + 7 1937-38 - 21 — 15 — 10 1938-39 - 5 — 10 — 13 1938-40 - 65 — 20.5 — 7 1940-41 - 80 — 33 — 16 1941-42 -133 — 27 — 26 1942-43 - 17 — 2 — 2 1943-44 - 49 — 43 — 3 1944-45 - 65 — 50 + 3 1945-46 - 22 — 4 — 3 1946-47 - 63 — 58 — 3 1947-48 - 29 — 5 0 1948-49 - 20 — 3 — 1 1949-50 - 50 — 2 — 6 1950-51 + 28 — 18 — 13 1951-52 + 4 + 5.5 1952-53 + 20 (N) - 12 (S) + 9 + 8 1953-54 - 49 + 3 + 7 1954-55 - 31 — 15 + 3 1955-56 - 47 — 1 + 4 Probably it would be possible to correlate stagnations and advances of Svínafellsjökull with terminal moraine ridges found within the 1904 limit of the glacier front but no attempt has hitherto been made at such a correlation. THE AGE OF STÓRALDA. Fig 3 shows soil profiles dug ancl measured in Öræfi in September 1955. Profile De 18a was measured on the crest of Stóralda proper near its highest point. Three tephra (= volcanic ash) layers could be identified in this profile. The thickest layer is without doubt the tephra from the eruption of Öræfajökull 1727 A.D. This layer is black, bastaltic and — due to the vic- inity of the volcano — more coarse grained than other recent tephra layers in the Öræfi profiles (particle diam. 5= 1 cm). During this erup- tion the main tephra fall was carried WNW- wards and the layer increases in thickness and coarseness towards N in the western part of Öræfi. The two black medium-coarse sandy layers immediately above the 1727 layer in this profile can hardly be other than the layers for- med by the eruption of Katla 1755 and the Laki eruption 1783. During the eruption of Katla in October 1755, one of the biggest from that volcano in historical time, the tephra was mainly carried eastwards. The tephra fall had a devastating effect in most of the inhabited area between Katla and Skeidarársandur and the tephra fall was also heavy in entire Austur- Skaftafellssýsla. (Safn t. s. fsl. IV, p. 243). The tephra layer from the Laki eruption 1783 is in Öræfi more finegrained than the 1755 tephra and the layer is thinner than one would expect from descriptions of this eruption. Upon the whole, the tephra production of the Laki fissure seems to have been much less than assumed by Thoroddsen. The devastating effect this erup- tion had on the vegetation nearly all over the country has partly been caused by poisonous gases such as affected the vegetation in the vici- nity of the jökulhlaup (glacier burst) in Skeid- ará 1954 (Thorarinsson 1954) ancl from which originated the bluish mist after which the 1783 disaster was called Móðuharðindi (The Mist Disaster). The black tephra layer found beneath the 1727-layer in profile De 18a has not yet been identified but it is likely to be from the erup- tion of Katla in 1625. 4

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Jökull

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