Náttúrufræðingurinn - 1953, Blaðsíða 27

MYNDIR ÚR JARÐFRÆÐI ISLANDS I
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fied and so it continued until the 3rd of May. During this period it mainly pro-
duced bombs and scoria but the production of fine-grained tephra (ash) was in-
significant although the crater might now and then emit black ashcharged cauli-
flower columns such as shown on Fig. 1. At the end of April it had already built
up a small but regular cone of scoria and bombs.
On May 3rd the activity of the crater changed character. The whirling up of
great lava pieces nearly ceased but instead it began puffing out almost continuous-
ly black fine-grained tephra and so it kept on until about the 20th of June. Its cone
was mainly built up during this period. After the 20th of June there were explo-
sions in the crater at increasing intervals until the middle of September.
On July 22nd 1947 Steinthór Sigurdsson determined trigonometrically the height
of the Summit Crater. It was then 1503 m and has not changed much since then.
According to measurements by S. Thorarinsson, carried out on Sept. 2nd 1947 the
max. relative height of the crater is ab. 90 m, max. depth 78 m, max. diam. (NE—
SW) 215 m, minim. diam. (NW—SE) 170 m, the volume of the tephra building up
the crater is ab. 5 mill. m3. The angle of outer slopes 30°—32°, of inner slopes
somewhat more, and the NW inner wall is partly precipituous (cf. the section,
p. 85).
The changes in the crater since the autumn of 1947 have been insignificant.
The crater rims still emit some vapour and the heat keeps the slopes mostly free
of snow. In June 1948 there was a considerable layer of snow in the bottom of the
crater but in Sept. 1952 it was quite snowfree.
Þess skal með þakklæti getið, að prentsmiðjan Hólar gaf Náttúrufræðingnum
prentunina á litmynd þeirri, er fylgir ofanritaðri grein, en prentmyndastofan Lit-
róf lét tímaritið fá myndarmótið það langt undir kostnaðarverði, að myndaserían
yrði tímaritinu ekki dýrari, en þótt myndirnar hefði allar verið svart-hvítar. Þess
má ennfremur geta, að litmyndin er gerð beint eftir litilli skuggamynd (25 X 36
mm), og hefur það ekki verið gert áður hérlendis, en mikið er tekið hér af slikum
myndum, og væri því mikils um vert, ef hægt yrði að litprenta sæmilega slíkar
myndir í íslenzk blöð og tímarit.