256 Russell — Massive- Solid Volcanic Eruptions. 



" In some cases when an upwelling of lava occurred [in the 

 Mono Craters] it barely entered the bottom of the bowl of 

 lapilli before becoming congealed. The eruption then ceased, 

 so far as that individual vent was concerned. At other times, 

 the thick viscid lava was forced up in the center of the crater 

 until it stood higher than the encircling rim of lapilli, but did 

 not expand laterally. In instances of this nature there is a 

 deep, moat-like depression between the rough and angular 

 protrusion of lava and the smooth inner slope of the encir- 

 cling crater, in which we may walk entirely around the central 

 tower-like mass. The type of this variety of eruption is fur- 

 nished by the crater shown in the following illustration [here 

 reproduced] which stands near the shore of Mono Lake, and 

 has been named Panum crater." 



The tower-like mass of lava in Panum Crater is not of the 

 nature of a cone of eruption, as is explained in the mono- 

 graph on Mono Valley referred to above, but a protrusion of 

 angular, massive rhyolitic lava the chemical composition of 

 which is given later in this essay. The lava at the time of its 

 extrusion was so nearly solid that it rose with essentially verti- 

 cal wall to a height of about 150 feet without exhibiting a 

 tendency to flow in any direction. In the light of the recent 

 example furnished by Pele, this protrusion of lava may be 

 accepted as being of the nature of a massive-solid eruption, 

 which occurred subsequent to the explosive eruptions that 

 built the* sharp-crested encircling crater of lapilli. 



The observations pertaining to a peculiar volcanic eruption 

 which occurred in Bering Sea in 1883, during which the shape 

 of Bogosloff Island was greatly altered, are discussed in " Vol- 

 canoes of North America," referred to above, and the follow- 

 ing conclusion as to its general nature presented : 



"Although not personally familiar with Bogosloff, I venture 

 to suggest, from what I have seen in connection with other vol- 

 canoes, that the formation of the island was due to the outwell- 

 ing of viscous lava, which hardened at the surfaces so as to 

 resemble the rough, scoriaceous surfaces so common in lava flows. 

 The lava, being quickly cooled, did not flow as a stream, but as 

 in the case of some of the Mono craters previously described, 

 rose in rugged scoriaceous masses, without much explosive 

 violence. Nothing resembling a crater ring of lapilli and dust 

 is reported as surrounding the elevated crags of lava." 



Here again the evidence, interpreted with the aid of the 

 more typical example furnished by Pele, indicates that a mas- 

 sive-solid eruption occurred. In this instance, the volcanic 

 conduit opened beneath the sea, . and the eruption was sub- 

 aqueous, but a protrusion of essentially solid lava took place, 

 the summit of which rose to a height of 325 feet above the 



