260 Russell — Massive-Solid Volcanic Eruptions. 



Without attempting to put on record at this time all of the 

 instructive features of the volcano on the border of Pauline 

 Lake, the facts in its history of chief interest in connection 

 with the study of massive-solid eruptions may be briefly enu- 

 merated as follows : 



The beginning of the eruption was characterized by the 

 occurrence of violent steam explosions, which blew away the 

 highly scoriaceous summit portion of the column of molten 

 material that rose in the conduit of the volcano ; the material 

 thus extruded consists mostly of light colored pumice, but 

 mingled with it are sharp-edged flakes of obsidian, and fell 

 about the opening from which it came so as to build a well 

 defined, sharp-crested crater with smooth slopes. The pro- 

 duct of these earlier explosions, together with the similar 

 material blown out at about the same time from four asso- 

 ciated volcanoes of the same character, was distributed widely 

 over the adjacent mountains. Succeeding the earlier and 

 most violent explosions, came an outwelling of viscous lava 

 which flowed northward down a moderately steep incline, but 

 did not spread widely and was so thick and viscous that it 

 came to rest with nearly vertical borders, the slopes of which 

 have since been reduced by the shattering of the glass of 

 which they are composed, and the fall of the fragments so as 

 to make steep talus aprons. After the discharge of viscous 

 lava, the central portion of the ascending lava column became 

 rigid and* was forced upward by pressure from below until it 

 stood, as at present, in massive crags, 250 feet high. Changes 

 of temperature have caused some shattering of the central 

 mass of stony andesite, but not nearly so much as in the case 

 of the surface of the neighboring obsidian lava-flow. Follow- 

 ing or accompanying the protrusion of the central crags, 

 renewed but minor explosions occurred about its base, during 

 which the rocks involved were broken and tossed about but 

 not thrown to a great height or widely distributed. Mingled 

 with the angular fragments now occupying the larger portion 

 of the crater and filling it nearly to the level of the part of its 

 encircling rim which remains, there is an occasional volcanic 

 bomb. These bombs have something of the characteristic 

 football shape common among such volcanic products. The 

 examples seen are about eight inches in diameter, and do not 

 show a " bread-crust " or other conspicuous surface features. 

 These masses were projected into the air during explosions in 

 a viscous condition, and received their rudely spherical shapes 

 owing to rotation about their longer axes during their serial 

 flights. They cooled before striking the ground and were not 

 flattened, and were not sufficiently plastic to adhere to the 

 loose stones on which they fell. Following the period of mild, 



