126 
VOLCANIC CRATERS AND EXPLOSIONS. 
of the still liquid, or, at any rate, pasty lava underneath, and rolls 
down the ends or sides of the stream with a very characteristic noise. 
Large fields of lava are thus commonly formed, covered with great 
rough, sharp-edged blocks, and they present an almost impassable 
barrier to locomotion. If the lava underneath the layer of scoriae retains 
sufficient heat to remain liquid long enough it parts with most of its 
imprisoned vapour, and may eventually emerge from under the covering 
and begin to assume the form to be next mentioned. Quite often, however, 
it originally contained little vapour, or has already lost the greater part 
when it comes out, and in this case it flows at once with a smooth surface. 
In either case this molten surface rapidly loses heat, and becomes treacly 
and viscid. The flow still continuing, this viscid layer is carried forwards 
and pushed up into a ridge like a cord, and solidifies in that form ; while 
the same happens to the surface of the portion which follows, so that another 
cord is formed behind the first, and the process is repeated till the stream 
or sheet of lava is entirely covered with corded structure. I watched this 
process on the Colle Umberto primo, the new hillock that formed on 
Vesuvius near the observatory in 1898 . The lava streams which were 
often numerous, were constantly cooling and giving place to new ones. 
They were not conspicuous by daylight, though they could be readily traced 
by the pale blueish vapour which they gave off.I At night, however, the 
red-hot lava became conspicuous in the darkness. A party of us watched 
the wonderful phenomena on every evening from the top of the observatory, 
and I was even able to secure photographs f of the streams by the light they 
themselves furnished. These lava structures must be contrasted with 
the products of explosive eruptions, such as ashes, scoriae and pumice. 
The great eruption of the Soufriere in St. Vincent was entirely 
explosive, and the ejecta were in places 200 feet thick. They consisted 
chiefly of ashes with a certain number of ejected blocks, and the secondary 
phenomena produced by the contact of rain water with the hot ash were 
very remarkable.* 
The eruption of Santa Maria f in Guatemala, in 1902 , was also entirely 
explosive. The mountain was previous to the eruption a very regular 
cone, about 12,600 feet high, with only quite a small crater in the summit. 
B y a series of tremendous explosions lasting two nights and a day, an 
entirely new crater was blown out of one side of the mountain. As nearly 
as I could measure it, it was seven-eighths of a mile in its longer diameter, 
and five-eighths of a mile in its shorter, while the precipice exposed in the 
side of the mountain was at least 5000 feet, say upwards of a mile, high. 
It is worth remembering that the corresponding precipice left after 
the eruption of Krakatau in 1883 , which has hitherto been considered 
one of the largest on record, is only about 1200 feet high. In both cases 
* T. Anderson and J. S. Flett, Phil. Trans., part i. 1902, parts ii. and iii. 1907; 
T t Anderson, Geographical Journal, 1902. 
f Slide shown, 
