Jaggar— Yolcanologic Investigations at Kilaiiea. 219 



currents, depth and temperature of the sinkholes themselves, 

 differences between conduits and sinkholes, and variations in 

 depth in the lake nnder diJfferent conditions and in different 

 places. It is hoped that work along these lines will be con- 

 tinued as opportunity offers. 



Smnmary of Depth and Consistency. 



Apparently our two queries are tentatively answered, and the 

 answer accords with the conception of lake magma and bench 

 magma outlined in this paper. The liquid lake in January, 

 1917, had a depth of about 50 feet (15 meters), with sinkholes 

 as downflow shafts, and conduits as inlets, distributed under 

 it and around its margins to the number of at least eight. 

 Secondly the lake magma, judging by its resistance to a sound- 

 ing rod, was of uniform viscous consistency beneath the crust 

 layer for approximately 40 feet (12 meters) of depth and increas- 

 ingly stiff to semi-solicl for the remaining 10 feet (3 meters). 



Conclusion. 



The main contributions of this paper to volcanologic science 

 as elucidated at Kilauea volcano are as follows : 



(1.) The lava column in Halemaumau pit at times of charac- 

 teristic activity is duplex. It consists, first, of a main serai- 

 solid incandescent body (bench magma), filling the whole true 

 crater from side to side for an unknown depth, perforated ver- 

 tically from below by several small shafts leading to a saucer in 

 its summit. Saucer and shafts are filled with the minor liquid 

 lava body (lake magma), which exhibits a more rapid convec- 

 tional circulation than the main body. The lake magma contrib- 

 utes substance to the bench magma by overflow and accretion 

 during a rise of the lava column. A slow circulation, which 

 resembles isostatic adjustment in its mechanism, is discernible 

 in the bench magma. During subsidence the lake magma 

 sinks more rapidly than the bench magma, uncovering portions 

 of the saucer. 



(2.) Magmatic gases, circulating by convection in the lava 

 column, are in tbe upper crater brought into contact w^ith 

 atmospheric oxygen mechanically by the circulation, which 

 acquires a superficial acceleration presumably shallow, and the 

 heat effect is sufficient to produce most, if not all, of the dis- 

 tinctive phenomena of tbe lake magma. 



Two antithetical conditions are realized in the crater by these 

 generalizations. The bench magma is a product seemingly of 

 solidification ahove normal viscosity^ and the lake magma a 

 product of liquefaction heloio normal viscosity. 



The normal lava column w^ould then seem to be of a sub- 

 stance not commonly revealed at the surface on Kilauea 



