SOME ELLIPSOIDAL LAVAS ON PRINCE WILLIAM 

 SOUND, ALASKA^ 



S. R. CAPPS 

 United States Geological Survey 



Many descriptions of elKpsoidal, spheroidal, or pillow lavas 

 have been published from time to time. Rocks of this type have 

 a wide geographic range and have been formed at intervals from 

 pre-Cambrian to the present. Various conclusions have been 

 reached by different writers as to the mode of origin of ellipsoidal 

 lavas, and the reasons for the development of their peculiar ellip- 

 soidal, spheroidal, or pillow-shaped forms. The ellipsoids or pillows 

 have been considered to be (i) concretionary, (2) the result of 

 brecciation, (3) due to contraction, (4) accumulations of volcanic 

 bombs, (5) the result of explosive eruptions, (6) and the result of 

 submarine cooling. In a recent article N. Sundius^ has well sum- 

 marized the important literature on the subject. 



Notwithstanding the various hypotheses which have been ad- 

 vanced to explain this phenomenon, it has come to be generally 

 accepted that the elhpsoids are the result of the flowing of the lavas 

 into water, or their extrusion under water, and are due to the rapid 

 cooling of the flowing molten material under these conditions. 

 Tempest Anderson^ has described recent pillow lavas actually seen 

 in the process of formation, and there now seems to be little reason 

 to doubt that the chilling of lavas under water is responsible for 

 many of the ellipsoidal lavas with which we have become familiar. 

 The purpose of this paper is to present certain facts which seem to 

 the writer to prove conclusively that the ellipsoidal lavas near 

 Ellamar, Alaska, were subaqueous flows, and to give certain criteria 



' Published by permission of the Director, United States Geological Survey. 



2 N. Sundius, "Pillow-Lava from the Kiruna District," Geol. foren. Fbrhandl., 

 Bd. 34, Haft 3 (1912), pp. 317-33- 



3 Tempest Anderson, "The Volcano of Matavanu in Savii," Quarterly Jour. Geol. 

 Soc, XLVI, No. 264 (1910), 621-39. 



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