394 JOURNAL OF THS WASHINGTON ACADEMY OF SClENCEvS VOL. 11, NO. 16 



crop or surface trace of the phosphate bed forms a sinuous line that sweeps 

 north and south, alternately bending sharply around the anticlines and 

 synclines. 



One hundred million tons of phosphate rock are estimated in reserve, of 

 which a considerable part lies above the natural drainage channels in situa- 

 tions especially favorable for mining. J. T. P. 



VOIvCANOLOGY. — The Katmai region, Alaska, and the great eruption of 

 IQI2. Clarence N. Fenner. Journ. Geol. 28: 569-606. 1920. 



A preliminary account is presented of observations made by the writer 

 as geologist of the expedition sent in 1919 by the National Geographic Society, 

 in cooperation with the Geophysical Laboratory of the Carnegie Institution 

 of Washington, to the Katmai region, Alaska. 



The volcanoes of this region, which form a continuation of the Aleutian 

 loop or festoon, are situated in an area of sedimentary rocks remarkable for 

 the absence of folding or obvious faulting. The more recent lavas are basic 

 andesites, contrasting greatly in composition with the highly siliceous rhyolite 

 of the last eruption. 



It is believed that in the fumarolic area of the Valley of Ten Thousand 

 Smokes the injection of a sill or closely similar body of magma into the under- 

 lying strata at the beginning of the eruption caused shattering of the rocks 

 above it, and these openings permitted the ascent of magma. The extrusion 

 and inflation of this magma gave rise to a great ash-flow or sand-flow, analo- 

 gous in many respects to the nuees ardentes of Pelee and La Soufriere, and 

 also led to the formation of the parasitic cone of Novarupta. The fumaroles 

 are thought to be due to the continued evolution of volatile constituents from 

 this body of magma. The development of the new vent of Novarupta is 

 ascribed to the enlargement of a channel along one of the fissures. The later 

 extrusion of the stiff lava forming the dome of Novarupta is found to have 

 been similar in many respects to that of the "spine" of Pelee. 



A study was made to determine the manner in which the top of Mount 

 Katmai disappeared and the great crater-pit was formed. It seems quite 

 certain that the material was not blown out directly, but must be accounted for 

 otherwise. Crater subsidence may have been a factor, but it is believed that 

 collapse of the crater-walls and incorporation of the material in the new 

 magma were chief features. It is recognized that the latter process demands a 

 large quantity of heat for its accomplishment, and the magma evidently was 

 not at very high temperature prior to extrusion; therefore accessions of heat 

 seem to be demanded. A considerable problem is thus presented, but it 

 does not seem at all insuperable, and it is believed that the evidences of solu- 

 tion are so strong that they cannot be disregarded. 



One of the important features of the eruption brings up for consideration a 

 phenomenon to whose significance little attention seems to have been paid 

 hitherto. It is that of a gas-charged magma gradually developing the explo- 

 sive condition after some interval has elapsed subsequent to its ascent from 

 the depths. The Katmai magma seems to have followed this com-se, and the 

 phenomenon is apparently not uncommon. This is believed to have great 

 significance and to imply changes of physical environment during its ascent, 

 effected with such rapidity that internal readjustments were not able to keep 

 pace with them. C. N. F. 



