476 PROF. G. DE LORENZO ON THE [Aug. 1906, 



20. The Eruption of Vesuvius in April 1906. By Prof. Giuseppe 

 de LoRENzo.'For.Corr.G.S. 1 (Eead May 9th, 1906.) 



After the great eruption of April 26th, 1872, the exhausted volcano 

 lapsed into comparative repose for three years, a repose marked by 

 merely solfataric phenomena, to awaken again in 1875, however, to 

 a state of strombolian activity, which continued until the beginning 

 of this present month of April, punctuated now and then by phases 

 of lateral outpourings of lava, such as those of the years 1885, 1889, 

 1891, 1895, etc. In the course of these the great cone was fissured, 

 and there flowed from the fissures month after month and year after 

 year, piling up on itself, a lava mostly of the Pahoehoe type, dense 

 and pasty, that is, insufficiently saturated with steam and superheated 

 water. 



Meanwhile, however, the quantity • of this water was slowly 

 increasing within the subterranean furnace, as was proved by the 

 great outbursts from the principal crater, which took place in May 

 1900 and September 1904. As the amount of this steam and the 

 degree of its tension continued to increase, on May 27th, 1905, 

 fissures were rent in the north-north-western wall of the cone, 

 whence rivulets of lava began to pour forth, from an altitude of 

 about 3600 feet. This went on until the beginning of the present 

 month of April, the new lava finding its way down the little valley 

 which runs between the two hills of lava heaped up by the 

 eruptions of 1891 and 1895, and flowing also westward in such wise 

 as to cut the electric railway along that portion of the track which 

 lies between the Observatory and the cable-railway. 



And now, on the morning of April 4th, the great cone, probably 

 unable to withstand any longer the increased tension of a magma 

 already saturated with steam, was cleft on its south-south-eastern 

 flank by long fissures, corresponding as to their axial planes with the 

 fissures torn in previous years in the opposite flank. On the 5th, 

 from the base of one of these freshly- opened fissures, near the Casa 

 Piorenza, at an altitude of some 2460 feet above sea-level, a small 

 stream of lava poured forth, while from the principal crater a great 

 jet of steam burst with explosive force, laden with scoriae and lapilli 

 caught up from the new cone. Then ensued a pause in the flow of 

 lava, during which interval the steam, now freed from an excess of 

 pressure, made ready for a fresh effort. 



And so, between the 6th and 7th of April, while the great 

 threatening pillar of black and brown lapilli was looming ever more 

 colossal towards the heavens, occupying well nigh one half of the 

 northern horizon, deeper and longer fissures than before yawned in 

 the south-eastern wall of the cone. Prom the orifice previously 

 mentioned, from another which opened up below the Valle delP 

 Inferno, and more particularly from a third, near the so-called 



1 Translated from the Italian by the Assistant-Secretary. 



