J. W. Shipley — Volcanic Emanations in Alaska. 149 



A series of surface temperatures was taken at ten- 

 yard intervals at a depth of four inches across a relatively 

 inactive area in the upper valley. The series extends 

 from the base of Mount Cerberus to a point 1160 yards 

 to the northward approximately half way across the 

 mud flow. 



The accompanying curve contains the temperatures 

 plotted against the distance. There are only two inter- 

 vals where the temperatures approximate normal, namely 

 the 170 to 300 yard interval and the 590 to 730 yard 

 interval. Both these areas are covered with water-de- 

 posited ash freshly lain after every heavy rainfall. Sub- 

 surface temperatures at a depth of twelve inches ran 

 from 7 degrees to 10 degrees higher. It follows, there- 

 fore, that the whole surface of the mud flow over which 

 this series extends has an abnormally high temperature 

 and is being supplied with heat from below. 



As the active vents are approached, the surface temper- 

 ature rises and remains relatively high until the activity 

 diminishes. It is over these areas that the hot volcanic 

 emanations are percolating through the porous mass of 

 the mud flow. The mud flow is either in intimate contact 

 with a heated mass of the earth's crust or the outlets for 

 the gaseous emanations from the magma are well dis- 

 tributed beneath the flow. 



Common origin of Novarupta Lava Plug and the Mud 

 Flow. — In order to establish any relationship of common 

 origin in the ejecta of the district, the silica, iron and 

 alumina in representative samples of the lava plug of 

 Novarupta, the Great Mud Flow, the Katmai Bed Mud 

 Flow and the pre-eruptive (1912) volcanics as repre- 

 sented in the rocks of Falling Mountain were determined. 

 The results follow: 



BocTc Si0 2 A1 2 3 Fe 2 3 



% % % 



Lava plug 75-2 14-2 3-2 



Great Mud Flow 73-7 13-8 3-8 



Red Mud Flow 63-6 18-4 7-8 



Pre-eruptive volcanics. . . 69-2 17-9 6-3 



It is rather interesting to note that the Katmai ejecta 

 and the old volcanics are of similar composition while 

 the lava plug of Novarupta and the Great Mud Flow are 

 much alike. The two latter apparently are of common 

 magmatic origin and differ markedly from the Katmai 



