>-^" r\ O TiT-Tr* *^O 



VOLCANIC FISSURES. 



may remark that in 1536 a fissure of this kind was _ 



which 12 cones were erupted one below another. In 1669 tne moun- 

 tain was split from the summit down two-thirds of its extent, and 

 from this fissure flowed the lava stream which destroyed Catania, 

 while upon it was built up the great double cone known as Monte 

 Rossi. On other occasions the lava has boiled out from fissures and 

 formed streams, all in the same line, at a number of points succes- 

 sively below each other. Some of these fissures have been traced, and 

 seen to be filled to a certain height with incandescent lava. One of 

 the latest examples was formed in 1874, and described by Professor 

 Orazio Silvestri, 1 who states that after the central crater had poured 

 out formidable columns of black smoke, sand, and scoriaa, a fissure 

 appeared on the north side of the central crater, which extended for 

 five kilometres, running east by north, and at a height of 2450 metres 

 was 50 to 60 metres wide where widest. Here a new elliptical crater 

 formed, and at its base ten small eruptive throats succeed each other 

 in a distance of 50 to 60 metres ; then others follow, so that there 

 are 22 minor cones in linear extension in a distance of half a kilo- 

 metre, and lower down there are 13 more cones, many of them only 

 a few yards in diameter. The superficial temperature of the lava 

 streams erupted was 70 cent. ; at a depth of half a metre it was 90 

 cent. This new mountain and its system of 35 subordinate cones and 

 lava streams, were all thrown up in a few hours. 



Fissure Eruptions. These fissure eruptions vary greatly in import- 

 ance. We have already seen that fissures on Etna may pour out 

 lavas without passing them through a volcanic cone, but it may be 

 useful to remember that this is the usual condition in Hawaii, and 

 that the eruption is then on a grander scale. A stream issuing from 

 a fissure in 1839, at a height of 1244 feet, flowed for twelve miles and 

 ran down to the sea. For three weeks this fiery river continued to 

 pour on, converting night into day. The reflected glare of the lava 

 was visible 100 miles at sea, and fine print could be read at midnight 

 at a distance of forty miles. When this lava entered the ocean, it 

 was shivered into millions of particles, which were thrown up in 

 clouds that darkened the sky, and fell like a storm of hail on the 

 surrounding country. With such materials, it will be readily under- 

 stood that lava-flows occur which are independent of ordinary volcanic 

 activity. Indeed, Yon Eichthofen regards massive fissure eruptions as 

 the more important and fundamental phenomena, conceiving that just 

 as a minor cone may be parasitic upon a main cone, so the ordinary 

 volcano is parasitic upon the subterranean part of a massive eruption. 2 

 But as a rule the massive eruptions form mountain-ranges and show 

 no signs of craters, though volcanoes occur on their lower slopes, or 

 form a parallel series of outbursts after the rock in the main fissure 

 has solidified. In such cases the rock-material is the same in the 

 massive outburst and in the volcano. 



1 "Notizie sulla eruzione dell' Etna, del 29 Agosto, 1874. Catania, 1874." 



2 "Natural System of Volcanic Kocks," Mem. California Academy of Sciences, 

 vol. i. part 2, p. 66. 



