234 Br. Anderson on Recent Volcanic Eruptions. [Jan. 23, 



When the greater part of the steam and gases have been discharged, 

 the hiva, still rising, gets vent either over the lip of the crater or 

 often through a lateral fissure, and flows quietly down the side of the 

 mountain. 



It is quite recognised that these phenomena may occur in various 

 relative proportions. We believe that in these Pelean eruptions, the 

 lava which rises in the chimney is charged with steam and gases, 

 which explode as usual, but some of the explosions happen to have 

 only just sufficient force to blow the mass to atoms and lift the 

 greater part of it over the lip of the crater without distributing the 

 whole widely in the air. The mixture of solid particles and incan- 

 descent gas behaves like a heavy liquid, and before the solid particles 

 have time to subside, the whole rolls down the side of the mountain 

 under the influence of gravity, and consequently gathers speed and 

 momentum as it goes. The heavy solid particles are gradually 

 deposited, and the remaining steam and gases, thus relieved of their 

 burden, are free to ascend. 



The effect of avalanches in compressing the air before them and 

 setting up a powerful blast, the results of which extend beyond the 

 area covered by the fallen material, has long been recognised. A 

 group of large trees was overthrown by the blast of the great ava- 

 lanche from the Attels on the Gemmi pass in 1895; all lay prostrate 

 in directions radiating away from the place where the avalanche 

 came down. 



[T. A.] 



