194 HAWATIAN ISLANDS. 
a volcano is surrounded by an elevation composed of ejected fragments 
of scoria thrown from the vent. Such cones are forming constantly 
at Vesuvius, one being no sooner destroyed by any great eruption 
before another commences and enlarges till often several hundred feet 
in height. But at Kilauea there is no trace of a cinder cone, notwith- 
standing the violence of the action. The great area that forms the 
bottom is a clean solid floor of hardened lava. ‘The peculiarity is not 
of difficult explanation. ‘To produce cinders, fragments or masses of 
lava must be thrown up by ejections high enough to cool before they 
fall. At Vesuvius, according to Sir James Hamilton, they rise at 
times to a height of 10,000 feet, and a thousand feet is a common 
elevation during the more quiet action ; the ejections take place usually 
every few minutes, and not continuously. At the last eruption of 
Teneriffe, in 1798, according to Mr. Colgan, the lavas were projected: 
to a height of 3000 feet. Compare this with the action in the pools 
of Kilauea, where sixty feet is the usual height of the jets when in 
the greatest violence, and where, consequently, the lavas, if they fall 
outside of the pool, melt together, as they are still fluid, and form a 
solid lava cone instead of one of cinders. 
But why this difference in the height of these ejections? It may 
be attributed principally to the greater mobility of the lavas of Kilauea. 
It is well known that the more free a fluid in its motions, the more 
freely and with the less agitation vapours or gases escape through it. 
In the more viscid liquid these rising gases become collected into large 
bubbles before sufficient force is gained to break way through,* and 
then the bubble bursts with a force approximately proportionate to its 
size. ‘The rapidity of their formation will influence somewhat their 
violence. Increase of force is derived also from a narrow vent, which, 
by the adhesion of its sides and the liquid, retards the bursting till the 
bubble has attained a larger size than could form in an open pool; 
* The mode of operation is well described by G. Poulett Scrope, Esq. Speaking of 
Stromboli, he says: ‘“‘ The actual aperture of this volcano, at the bottom of its semi- 
circular crater, is completely commanded by a neighbouring point of rock, of rather 
perilous access, from whence the surface of a body of melted lava, at a brilliant white 
heat, may be seen alternately rising and falling within the chasm which forms the event 
of the voleano. At its maximum of elevation one or more immense bubbles seem to form 
on the surface of the lava, and rapidly swelling, explode with a loud detonation. This 
explosion drives upwards a shower of liquid lava, that cooling rapidly in the air, falls in 
the form of scoria.” This action in constant repetition is described as the permanent 
characteristic of its eruptions.—Conszderations on Volcanoes, p. 17. 
