34 J. D. Dana — History of the Changes in Kilauea. 



and processes are the same whether the lavas fill up to the 

 summit before outflowing, or become discharged at a lower 

 level by an opened fissure. 



Examples in the Hawaiian Islands teach also that volcanoes 

 may end with an open crater over 2,000 feet deep, like Halea- 

 kala, a cone 10,000 feet high, or with a filled crater, as in 

 the case of Mt. Kea, 13,800 feet high. 



The preceding remarks about the permanence of craters 

 apply to other kinds of volcanoes as well as the basaltic ; but in 

 the form of the crater the basalt volcano has peculiarities, owing 

 to the mobility of the lavas and the paucity of cinder dis- 

 charges. The ordinary crater of such volcanoes is pit-like, 

 with the walls often nearly vertical, and the floor may be a 

 great, nearly level plain of solid lavas. The liquid material 

 of the extremity of a conduit works outward from the hotter 

 center, through the fusing heat and the boiling and other 

 cauldron-like movements ; and hence, where the mobility 

 favors freedom of action in these respects, it tends to give the 

 basin or crater a nearly circular form with steep sides — an ex- 

 planation I give in my Expedition report. Besides, when the 

 discharge takes place there is usually a fall of the walls which 

 is still another reason for vertical sides, and the pit-like form. 



The small lava-lakes of Kilauea, and the Great South Lake 

 also after a discharge, (or an eruption as it is usually called) 

 are literally pit-craters. Such was the condition of the Great 

 Lake after the eruption of 1886. They all illustrate how the 

 great pit-crater, Kilauea, was made. The lower pits of 1823, 

 1833, 1840 are other examples. 



Such pit-craters are normally circular ; but where there is a 

 large fissure beneath the crater, they may be much elongated. 



From the considerations which have been presented we see 

 why the volcanic mountains of the Hawaiian Islands, with 

 slopes rarely exceeding 10° in angle, differ so widely from the 

 great andesyte cones of western North America, with their 

 high slopes of 28 to 35 degrees. We see that the fact of be- 

 ing basalt-made means much in a volcano ; that it affects pro- 

 foundly all the movements and the results of those movements 

 as well as the shapes of the mountains and of their craters, 



[To be continued.] 



