654 WILLIAM HERBERT HOBBS 



destruction of the crater and great reduction in its height. The 

 exposure within the fractured crater of larger surfaces of the hitherto 

 imprisoned lava allowed of the more rapid escape of steam, which 

 produced much more violent explosions. The fragments and 

 lapilli, lifted by the uprushes of steam, were distributed by a south- 

 westerly wind over the cities at the northeastern base of the mountain 

 and beyond. The clefts opened being on the south side of the cone, 

 hocche were there formed and the lava streams following the slopes 

 descended respectively toward Trecase, Boscotrecase, and Ter- 

 zigno. The rapid descent of these great lava bodies is explained 

 both by the steep slopes and by the head under which they flowed — 

 the difference in elevation of the new hocche (near the piano) and 

 the old one high up upon the central cone. The pressures now 

 relieved, the closing phases of the eruption followed in the slow 

 escape of the remaining steam within the lava of the crater, now 

 doubtless covered with ash shaken down from the walls. Much 

 of this ash was probably again and again sent up to fall in considerable 

 part within and about the crater, the finer portions only making 

 contribution to the comminuted material derived from the rapid 

 expansion of the steam within the lava itself. 



Mutual relationships of tectonic movements and volcanic erup- 

 tions. — Few. facts have been more securely established by experience 

 than the lack of correspondence in time of great earthquakes and 

 volcanic eruptions, in those regions where both are common. It 

 has even been shown by Milne that central Japan, where there are 

 many active volcanoes, is singularly free from earthquakes. Yet, 

 while there is apparent lack of quick sympathetic response of the one 

 phenomenon to the other, evidence is not wanting that the influence 

 of the one slowly makes itself felt upon the other. Milne has shown 

 that the West Indian earthquakes have been broadly related in 

 time to the greater outbursts of its volcanoes.^ Suess'' long ago 



two in the early morning of the 8th. It may be significant that there were three main 

 lava streams, all of which appear to have started at about this time and apparently 

 from separate, though near-lying, hocche. 



1 John Milne, " Seismological Observations and Earth Physics," Geographical 

 Journal, London, Vol. XXI (1903), pp. 15 £f. 



2 Ed. Suess, "Die Erbeben des siidlichen Italien, " Denkschriften der Wiener 

 Akademie, Mathematisch-Naturwissenschaftliche Klasse, Vol. XXXIV (1872), pp. 1-32. 



