jaggar: thermal gradient at kilauea 399 



The writer determined by sounding on January 23, 1917, that 

 the liquid lava in the lake was 14 meters deep, and that it rested 

 on a seemingly pasty resistant bottom. This bottom was par- 

 tially uncovered and revealed by subsidence of the liquid part 

 of the lava column in February, 1917, confirming the soundings. 

 Soundings of the remnant liquid pool on March 24 showed that 

 the depth had diminished to 9 meters. After rising had been 

 resumed, on May 2, the depth at the same locality was 13 meters. 

 The liquid of the lake magma rises through conduit wells in the 

 bench magma and circulates by convection through the conduits 

 and sinkholes, the semi-solid bench magma forming the lake 

 bottom and margins. 



The thermal gradient of the liquid lake to its bottom is not 

 the gradient of the lava column. That could only be deter- 

 mined by profound soundings along with temperature measure- 

 ments in the conduits and sinkholes. The liquid lake is a shallow 

 pool of lava continually engulfing vesicular crusts, which must 

 be full of air, and which do not melt at once, as the upper tem- 

 peratures are not those of superfusion. The determination of 

 the gradient of the pool is of interest to show (1) whether re- 

 action between gases rising from the bottom produces increased 

 heat upward, or (2) whether surface radiation and expansion 

 of the gases in vesicles make a graded cooling effect upward, or 

 (3) whether a combination of these two processes, and also sur- 

 face oxidation of the gases, bottom oxidation due to foundered 

 crusts containing air, or bottom radiation, in some way compli- 

 cate the curve. That it is a smooth curve seems unquestion- 

 able. Condition (3) seems nearest the measured gradient. 



The measurements of 1917 are divided into three groups: 

 group 1 (indicated by triangles in the accompanying diagram), 

 January-March reconnaissance of method and surface temper- 

 atures ; group 2 (indicated by crosses) in which the upper grad- 

 ient was accurately determined in April with small steel pipes 

 as containers of Seger cones; and group 3 (dots, A and B), 

 lower gradient determined May 2 with special apparatus, the 

 corrected error being due to air cushion in large pipe. It was 

 found in the earlier experiments that pipes from 3 to 8 cm. in- 



