March 21, 19 18" 



NATURE 



55 



I 



always the pasty bottom was found at fewer than 50 ft. 

 of depth, with due allowance for the angle of immersion. 

 This discovery, however, checked perfectly with the 

 results of continued observation 

 and survey which had repeatedly 

 made record of shoals appearing 

 in the lava, and of cascades 

 from the liquid lake into mar- 

 ginal voids and over submerged 

 ledges, after a period of subsi- 

 dence. These hitherto unex- 

 plained facts at once became in- 

 telligible when it was realised 

 that the lava column in reality 

 is a semi-solid body filling the 

 true crater from side to side, 

 while the liquid lake is a gas- 

 heated froth maintained through 

 conduit holes honeycombing the 

 upper part of the harder column. 

 The basin of the lake is a 

 shallow saucer, and convectional 

 circulation keeps the liquid lava 

 in motion. The famous islands 

 and benches are of the bench 

 magma, or semi-solid substance 

 which forms the bottom of the 

 liquid lake. 

 Thermal Gradient of Lava Lake. 



With batteries of Seger cones 

 encased in iron netting and 

 strung on a wire, which in turn 

 was placed within long steel 

 pipes, measurement was mad<' 

 in 19 17 of the thermal gradient 

 (Fig. 2) of the liquid lava pool. 

 Individual temperature measure- 

 ments were also made of the 

 fountaining grottoes at the mar- 

 gin of the lava and of flarning 

 c h i m n e y s through blowing- 

 cones above it. The highest 

 temperatures, about 1350° C, 

 were found in this air zone of 

 free oxidation of gases ; the 

 fountaining lava reached a 

 maximum of about 1180° C, the 

 bright lines of the lake surface 

 were at about 1000° C, while 

 just below the surface the tem- 

 perature was 100° lower. From 

 here to the bottom of the lake 

 40 ft. down there was rising 

 temperature. A thick lower 

 stratum of the shallow- lake 

 showed uniform temperature 

 between 1100° and 1200°. 

 This lower stratum prob- 

 ably represents reheating due to 

 oxidation of gas in contact with 

 air carried down by foundering 

 crusts. The fall in temperature 

 towards the lake surface from 

 the bottom up, which in the 

 middle region amounts to 70° C. 

 per metre, is due to surface 

 radiation aided by gas expan- 

 sion . The localised surface heat- 

 ing is due to surface oxygen and 

 completion of reactions between rising unstable gas 

 mixtures. 



Dermolith and Aphrolidh. 



The writer has proposed these terms for fluidal lava 

 and block lava respectively, called pahoehoe and aa by 

 NO. 2525, VOL. lOl] 



the Hawaiians, because, as the result of the investiga- 

 tions here recorded, he believes dermoHthic versus 

 aphrolithic process to represent respectively the lique- 



FlG. I. — Map and diagrammatic section of Halemaumau, January 12, 1917. Lava lake in black, crusted 

 conduit ponds shaded, overflow benches diagonal line<, raised crags contoured. Coarse dotted outline, 

 lava lake of February 18, 1912. Fine dotted outline, June 23, 1916. Rectangle (5), site of lava spring of 

 June 5, 1916. Rectangle (6), west corner of pool June 6, 1916. Note that N.W. corner has been conduit 

 source on all these dates. Sliebt slope lake surface from conduits W. to overflow bench E. Bench 

 magma elevated on conduit side W.S.W., subsided on sinkhole side E. N. E. Section without vertical 

 exaggeration, lower profile shows simple rising pool of June 23, 1916. Shoal shown in lake bottom was 

 revealed by subsidence February, 1917. Di;pths Irom soundings and subsidence records. Note 

 progressive shoalings from W. to E. Diagrammatic sinkhole E. shows ridge of accretion on lake bottom 



lagrammatic 

 hen subside 

 Bench marks (B.M.) IJ..S. Geological Survey, trig 



at Halemaumau.— From Amer.Jout^. 6V/., September, 1917. 



margin which produces cascade ledge when subsidence takes place. Surveys with transit byT. A. Jaggar. 

 "" ~ ~ • ■ • " stations Hawaiian Volcano Observatorj-. Nlendian 



faction of lake magma and the gas expansion solidifi- 

 cation of bench magma. The dermoHthic basalts of 

 Kilauea crater, characterised by wrinkled skins, have 

 sufficiently adjusted and diminished their gas-bubble 

 content to solidify from without inward. The aphro- 



