VESUVIUS 377 



Since 1906 the volcano has been in a solfataric state, no outflows of 

 lava or definite explosions having taken place. With the exception of 

 certain portions of the crater floor, to be mentioned later, the changes 

 have been largely those due to non-volcanic agencies. 



Fumarolic activity began shortly after the cessation of the eruption ; 

 that is, as soon as the vapors could open a way through the superincum- 

 bent ash. The chemical effects of these hot, very acid gases have, of 

 course, considerably disintegrated the rocks and have contributed ma- 

 terially to the progressive demolition of the cone. 



In the Atrio del Cavallo, close to the face of Monte Somma, is a group 

 of about 30 fumaroles, some of which are shown in plate IG, whicli re- 

 semble the so-called hornitos of Jorullo. These have been described 

 especially by Malladra^ and Bernardini.^ They have formed relatively 

 low, domal elevations, from one to eight meters high, with circular or 

 elliptical outlines, elongated parallel to the Somma scarp. These accu- 

 mulations are composed of ashes and claylike decomposition products, 

 cemented by sulphur and various salts, chiefly sulphates. Those which 

 form a row nearest the central cone have a constant temperature of about 

 97° C, and the analyses of the gases by Bernardini show a decided per- 

 centage (7-11) of HoS. Those in the next row show about the same 

 temperature, tliough somewhat variable and with only traces of HoS, 

 while those nearest the Somma scarp are still more variable in tempera- 

 ture' and willi IK) IToS. At tlie time of our visit the activity of all these 

 fumaroles appeai'cd to b;i\c diminished nearly to the point of extinction. 



The fiiniaroles inside the crater are of special interest and were in a 

 state of considerable activity, the humidity which prevailed during our 

 stay rendering them more prominent than would have been the case in 

 dry weather. Some were also in action on the upper part of the outer 

 slope, these being confined to the north and northeast sections. The tem- 

 peratures of these have been measured by Perret,. Mercalli, Malladra, and 

 Friedlander and are somewhat variable. Their temperatures and activity 

 seem to be decreasing. 



Inside the cone fumaroles were in activity in all parts of the walls. Of 

 these, those on the north and northeast form a prominent group, or 

 "battery," as such a line of fumaroles has been named by Mercalli. The 

 temperatures of tUesL' have not been measured, as they are inaccessible. 



The largest, most prominent, and most active battery is on the south- 

 west and west inner scarp. These begin in the southwest, below the point 

 to which tourists are taken by the guides, about 20 meters al)<)ve the 

 bottom of the crater, and extend obliquely upward to a ]Miirit l)elow the 



« A. MiilliHlrii : Ucml. Ac. Scl. Nap., vol. xlx, 1S)13, p. ir.:j. 

 T I.. HiMiiuidiiii : Ki'ud. Soc. CLlui. Itul. Niip.. 1913. 



