ETNA 381 



tiowed almost due south for a distance of about 10 km., nearly reaching 

 the Monti Rossi, near Nicolosi.^ 



It was succeeded by a period of strombolian activity in the central 

 crater, and at tlie end of May, 1911. a lai'.ue bocca opened on the main 

 platt'oi'm, northeast of and close to the summit cone.^ This was followed 

 by a short but \ iolent eruption in September, 11)11, on tbe northeast 

 tlank, but far down the mountain, some 6 km. from the summit.'" Since 

 then the volcano has been quiescent and fj-enerally in a solfataric condi- 

 tion, with only occasioiial strcmibolian activity. 



Tlie summit crater of Etna is situated approxiniatel\' in the center of 

 an ash cone 1,()()0 feet hioh rising from the Piano del Lago (cf. ])late IT). 

 It is nearly circulai' in form, about 500 meters in diameter, and receives 

 its color for the most part from fresh, light gray asii which, dni'ing tlie 

 period of tnir visit, was thrown out almost daily. The crater rim, except 

 for a small section just above the observatory, is a sharp edge formed by 

 the steep outer slope of the cone and tlie precipitous wall within, due to 

 slips which the extensive concentric cracks show^ to be the present process 

 of enlargement of the crater. The inner walls, with the exception noted, 

 are nearly vertical near the top, and will average 90 per cent in pitch 

 froiii to]) to bottom Oil the northeast, north, west, and southwest walls. 

 The southeast wall appears to have sagged rather than broken ahrui)tly, 

 and presents a somewhat rounded contour both outward and inwai'd for 

 a i'i'W meters, beyond which it breaks abruptly over a talus pile on the 

 bottom of the crater below. The depression caused by this sagging is no 

 iiKtre than \~y or 20 meters. It affords a platform from which a beautiful 

 \ icu of the intefioi' of the crater can be obtained in those i-ure intervals 

 when the (;rater is free of smoke. It is, nevertheless, a most treacher- 

 ous point because of the concentric cracks which cross it and which have 

 hfcn bi-idged over by recent ash so as to be entirely invisible. The view 

 of the crater shown in plate 18 was taken from this point. 



At the time of our visit in June and July the central cone and the 

 suri'oiiiiding plateau wei'e covci'ed with a layer of line, ilark gray ash, 

 iVoin I.') to ."ill i-ni. thick, with many small stones (10 to ."lO em. diameter) 

 iiiilieddcd III the ash. The greater part of this had fallen about two 

 months p!'e\ ioiisl v. according to Allio liai'hagallo. the custodian id the 

 ob.servatoi'v. It is ipiitc practicable to walk entirely aroun<l the rim of 

 the crater, though the fo<iting is e\er\ where slini\ and the ga>e> to lee- 



" The best descrii>lii>iis of lliis cnijiiioii aii' ii> I"- limnd in impers \<y S. .VrcirtlaooiKi. 

 A. Ulcco, O. de Fioif. I". N'iiiassa de Ki-Kiiy. 1'. Sit ila Starrublm. and I., rafrara in .\ttl. 

 Aw. (iloen. (5). vol. iv, lull, and in a papt'i- liy <!. 1'onte in .\ttl. .\i'<-. Line. iri). vol. 

 vlll, li»ll, p. iW.'.. 



" ( 'f. .\. Kicco: .\lli. .\i-c. (Uwn. i ". I , vol. iv, llMl, nicni. xi. 



••Gaetano IMalanla ; Hlv. tleog, Ital., vol. xlx. 1!»1L*. 

 G. Ponte: Boll. Ciiil) Aip. Ital.. vol. xll. 10i:i. No. 74. 



