240 HOVEY— EARTHQUAKES : [April 24. 



some observers, indeed, had noted an increase of seismic shocks for 

 a year or more before the volcano burst into violent eruption in 

 May, 1902. The eruption itself, however, was free from earth- 

 quakes, except apparently for the quivering of the mountain due to 

 the uprush of steam and ejecta through the conduit, just as hap- 

 pens in the chimney of a fire engine under full blast. The chattering 

 vibrations thus set up in the volcano shook a narrow strip of recent 

 beach formation from the west base of the mountain, where the 

 declivity of the shore is considerable. 



Vesuvius being the volcano that has been most continually and 

 thoroughly under observation throughout its known history, we 

 naturally look to its records for light upon the relation between 

 volcanic eruptions and earthquakes. When this old center, which 

 was not known to the ancients as a volcano, renewed its activity in 

 the year 79, the first phase was a series of earth shocks which in- 

 creased in frequency and severity until the afternoon of August 24, 

 when the eruption actually began. The ground is said to have 

 rocked to and fro like the sea, but we read of no great damage as 

 resulting therefrom even in Pompeii and Herculaneum at the very 

 base of the mountain. The outbreak of 163 1 occurred after centuries 

 of repose and was heralded by a half year of earthquakes and terrific 

 noises in the interior of the mountain. This history has been re- 

 peated again and again in greater or less degree, particularly when 

 the eruptions have been of the explosive kind. According to the 

 report of A. Lacroix, violent earth movements shook the cone of 

 Vesuvius during the great eruption of April, 1906, and were felt 

 throughout much of the surrounding region. Whatever effects have 

 been produced have been local in extent and comparatively light 

 in degree. 



The eruptions of Etna usually have been accompanied by the 

 formation of great fissures in the upper part of the cone, and the 

 opening of these fissures has been accompanied by severe vibra- 

 tions of the surface of the mountain, as has been vividly portrayed 

 by Silvestri in his account of the eruption of 1879, but the shocks 

 seldom affect the mainland of Calabria across the narrow Strait 

 •of Messina. Stromboli, the " Lighthouse of the Mediterranean," 



