342 VOLCAlNriC eruptions on MARTINIQUE AND ST. VINCENT. 



explosions and the degree to which the ascending steam is debris- 

 charged. If the energ}" is great and the upward propelling force 

 essentially constant, it may well be inferred that the column, as 

 explained bj' Jaggar, will attain a great height before the resistance it 

 offers to the ascent of fresh material causes an expan>?ion at the base. 

 If, howe^'er, the steam driven out at any stage in an eruption is exces- 

 sively loaded with debris, an expansion and overflow at the rim of a 

 crater might occur, no matter whether the fall of previously discharged 

 material from aloft had begun or not. The essential feature in a down 

 blast from a crater seems to be that heavily debris-charged steam 

 behaves in many ways like a fluid and will flow down steep gradients 

 and acquire great velocity when the slope and other features of the 

 surface over which it progresses are favora])le. The gradients on 

 the slopes of Mont Pelee and La Souf riere, within the zone of destruc- 

 tion in each case, are about l.OOO feet to a mile. and. as seems evident, 

 the Anally accepted explanation as to the contrt)lling condition which 

 gave direction to the blasts which swept them will include the prin- 

 ciple just stated. In this connection it is instructive to note certain 

 observations made by Messrs. Andei'son and Flett, conmiissioners sent 

 l\y the Iloyal Society of London to study the recent eruptions. On 

 the evening of rTidy i) these genthMueii were on a vessel near C4irl)et 

 and witnessed an eruption of Mont I^elee. 



''As the darkness deepened, a dull red reflection was seen in the 

 trade-wind cloud which covered the mountain summit. This became 

 brightcM' and brighter and soon we saw red-liot stones i)rojected from 

 the crater, l)owling down the mountain slopes and giving oft" glowing- 

 sparks. Suddenly the cloud was brightly illuminated, and the sailors 

 cried, 'The mountain bursts!' In an incredif)ly short space of time a 

 red-hot avalanche swept down to the sea. We could not see the 

 sunnnit owing to the intm'vening veil of cloud; l)ut the Assure and 

 the k)wer parts of the mountain were clear, and the glowing cataract 

 poured over them right down to the shore of the l)ay. It was dull 

 red, with a billowy surface, reminding one of a snow avalancii(\ In 

 it there were large stones, which stood out as streaks of bright red, 

 tuml)ling down and emitting showers of sparks. In a few miiuites it 

 was over. A low, angry growl had burst from the mountain when 

 this avalanche was launched from the crater.'' 



The time occupied by the avalanche^ to reach the sea was "possibl}^ 

 a couple of minutes. It could not have been much more." * * "' 



"There is no doubt that the eruption we witnessed was a counter- 

 part of that which destroyed St. Pierre. * * * The most peculiar 

 feature of these eruptions is the avalanche of incandescent sand and 

 the great black cloud which accompanies it. The preliminary stages 

 of the erui)tion, which may occu])v a few days or oidy a few hours, 

 consist of outbursts of steam, ftne dust and stones, and the discharge of 

 the crater lakes or torrents of water or nuid. In them there is noth- 

 ing unusual, but as soon as the throat of the crater is reached, a mass 

 of incandescent lava rises and rolls o\'er the lip of the c-i'ater in the 



