404 jaggar: thermal gradient at kilauea 



compete with enormously rapid radiation and crusting, which 

 latter ordinarily is greatly dominant. The fall in temperature 

 upward through a surface crust 8 cm. thick is fully 400°; the rise 

 in temperature from the region a half-meter below the crust to 

 the " bright lines" amounts to from 100° to 150°, and to the 

 fountains 250° Heavy crust may form in thirty minutes and 

 is a porous insulator from the heat of the melt beneath such that 

 a man could stand on it for an instant without suffering. Thin 

 crusts form instantly and continuously, the "bright lines" 

 being wavy bands on the lava surface at the margin of the rending 

 crust, the up welling melt and gas eroding the air-filled vesicles 

 of the crust. Thus heat-generation ensues, through completion 

 of the reaction between rising unstable gas mixtures and through 

 union with atmospheric oxygen. Foundering of crusts liberates 

 much heat, carries down air, and induces fountaining. 



It will be seen that the hypothetical gradient of cooling effect 

 carried to the heavy crusts, disregarding the reheating due to 

 surface reactions, would exhibit no bend upward to the right as 

 in the diagram at depth 1 meter, but rather a curve to the left 

 ending on the surface at about 400° (C in diagram). A com- 

 pletely crusted pool therefore, with gas reactions satisfied else- 

 where, might reveal very low temperatures just beneath the 

 surface in accordance with curve C This may account for 

 some of the anomalous records of group 1 (triangles), and others 

 not here recorded which the writer has obtained with a thermo- 

 couple. It is hoped to explore this surface region more com- 

 pletely. 



The zone of cooling from depth 7.5 meters to the surface 

 crusts registered an average loss of temperature upward on May 

 2 of 70° per meter for the lower 3 meters. This middle region 

 would appear to suffer a marked bend in the gradient from a 

 relatively heated zone beneath. The viscosity should thus in- 

 crease rapidly from depth 7.5 meters to depth 1 meter, a condi- 

 tion favorable for confinement of large gas bubbles beneath the 

 zone of surface heating. The cooling is in the main due to sur- 

 face radiation, aided doubtless by gas expansion. The surface 

 heating appears to be localized and sudden, occurring as a result 



