June 7, 1877] 



NATURE 



10: 



THE VOLCANOES OF ICELAND 



TOURING the past year the Danish Government de- 

 '—^ spatched the well-known geologist, Prof. Johnstrup, 

 to Iceland, for the purpose of making a thorough scien- 

 tific investigation of the scene of the recent volcanic dis- 

 turbances. A short time since he laid before the Danish 

 Parliament a report of his journey, with a brief account 

 of the results so far obtained. The first part of the ex- 

 jiedition was devoted to the volcanoes in the Dyngju 

 Mountains, encircling the valley of Askja, and was 

 accompanied with many difficulties resulting from the 

 conformation of the region and the prevalence of violent 

 snow-storms. The mountains themselves are not of 

 volcanic origin, but consist of basalt and palagonite- 

 breccia. In former times the Askja Valley was evidently 

 much deeper than at present. Repeated flows of lava 

 have gradually filled it up, and these Prof. Johnstrup be- 



lieves to have occurred within the historic period, although 

 no mention of volcanic disturbances in this district is to 

 be found in the annaU of ihe island. Along the outei 

 edge of the Dyngju Mountains are numerous craters, 

 some of considerable size, which have contributed most 

 of the lava covering the plain of Odadahrann to the ex- 

 tent of sixty square geographical miles. Part of this 

 enormous cjuantity of lava had its origin in the neigh- 

 bouring volcano of Trdlladyngja. It is, however, sharply 

 distinguished from the twisted, contorted, masses of the 

 former, by its more regular character and smooth cruets. 

 In the neighbourhood of the newly-formed craters the 

 earth is covered to the distance of over a mi e with the 

 bright yellow pumice-stone ejected during the eruption of 

 March 29, 1S75. Most of the pieces are seven to eight 

 inches in diameter ; many contained two to three cubic 

 feet. In places where the pumice-stone is several 

 feet in depth, it covers a layer of snow twenty-five 



feet deep, which fell in the wmter of 1874-1875, and 

 has been protected from the effects of solar warmth by 

 the feeble conductive power of the pumice-s^one. It is 

 fortunate for the land that the outbreak was of this nature, 

 for from its lightness the pumice-stone can be easily 

 removed from the surface of the country. The party 

 examined the most northerly of the craters, which was 

 300 feet wide and 150 feet deep. It was filled with steam, 

 which was driven out with such force as to give rise to a 

 most deafening roar. No solid matter, however, was 

 borne along with the vapour. Not far from the crater an 

 extensive depression in the valley of Askja has taken 

 place, and the fresh surfaces of rock exposed thereby give 

 a clear picture of the peculiar formation of the valley by 

 successive deposits. It presents a remarkable similarity 

 to the basalt and dolerite formations so prevalent in the 

 mountain ranges of Iceland. 



The most surprising feature of these late eruptions was 

 the ejection of such enormous masses of pumice-stone, 

 while not a trace of a lava stream is to be found. A similar 



outbreak is not mentioned in the records of the island. 

 On account also of the vast development of steam, which 

 gave rise to the pumice-stone formation, they are without 

 a parallel amongst volcanic phenomena. At present the 

 craters are to be regarded as gigantic steam escape tubes, 

 the activity of which will continue for an uncertain period, 

 but with gradually decreasing intensity. As long as these 

 safety valves remain open it is not probable that a repe- 

 tition of the eruptions will occur in the immediate future. 



The volcanoes in Myvatns Orai-fi were found to pre- 

 sent entirely different characteristics. This barren plain 

 is about tliitty-five miles long and thirteen miles wide. 

 Suddenly, on February 18, 1875,3 volcano appeared in 

 the centre. Four others appeared at subsequent dates, 

 all of the craters falling into a straight line north and 

 south. No eruptions have occurred here within historic 

 times. The mass of lava which issued from these various 

 craters is estimated at 10,000,000000 cubic feet, eighteen 

 times the amount supposed to have been emiited by 

 Vesuvius in 1794 and 1855. The lava was basaltic and 



