130 CARNEGIE INSTITUTION OF WASHINGTON. 



PETROLOGY OF HAWAIIAN ISLANDS. 



As an outcome of the First Pan-Pacific Congress, held at Honolulu in 1920, 

 a study is being undertaken of the Petrology of the Hawaiian Islands. For 

 this there is available the largest collection of Hawaiian lavas that has yet 

 been brought together, including many specimens collected by H. S. Wash- 

 ington in 1920, a large collection made by Dr. Sidney Powers, and smaller 

 collections made and contributed by several other geologists. These speci- 

 mens, which number about 1,500, represent very well all islands of the group. 



The study of the five volcanoes (Kohala, Mauna Kea, Hualalai, Mauna 

 Loa, and Kilauea) on the island of Hawaii has been completed and the results 

 have been or are being published in a series of papers in the American Journal 

 of Science for 1923. The study embraces petrographical descriptions and 

 many new chemical analyses, which bring out clearly the characters of the 

 different types of rock and their relations to each other at the different 

 volcanoes. The relative ages of the five volcanoes are discussed, and it is 

 shown that each one differs more or less from the others in the general and 

 in the detailed characters of its lavas. It is shown that, although the Hawai- 

 ian lavas are for the most part basaltic, yet there are some very significant 

 differences even within this comparatively narrow range. Also, light is 

 thrown on the affinities and probably the origin of the very alkalic rocks 

 (trachyte and oligoclasite) of Hawaii, and on the origin of some very basic 

 olivine-rich lavas that are near the other extreme. The study of the Hawaiian 

 lavas furnished many excellent illustrations of the validity among natural 

 lavas of Bo wen and Andersen's experimental observations on the origin of 

 olivine, which were made in this Laboratory some years ago (Publication 

 No. 172). The studies lead also to an explanation of the cause of the differ- 

 ences between the two chief types of basaltic lava — aa and pahoehoe — 

 which are very common at the Hawaiian and other volcanoes, and for which 

 no adequate explanation has yet been given. 



The study is being prosecuted and extended, with the addition of many 

 more analyses, to the lavas of the other islands of the group, and should be 

 completed in 1924, when the final conclusions based on the complete data 

 will be discussed. The results already obtained throw light on certain prob- 

 lems of the petrology of the other volcanic islands of the Pacific, indicating 

 that the lavas of the Hawaiian Islands probably represent the lavas of many 

 of the intro-Pacific islands fairly well. It is therefore of importance, both for 

 our knowledge of the Pacific volcanoes and of volcanoes in general, that the 

 present studies be continued and extended. It is desirable that the study 

 of many specimens of lavas from the Pacific volcanoes, especially a large 

 number collected by the late Dr. J. P. Iddings and by Professor W. H. Hobbs, 



be not unduly delayed. 



VOLCANO STUDIES. 



In the annual report of last year there was reviewed at considerable length 

 the first of a series of papers on the volcano and fumarole activity associated 

 with Katmai Volcano, Alaska (Paper No. 485, E. T. Allen and E. G. Zies, 

 "A chemical study of the fumaroles of the Katmai region," Nat. Geog. Soc, 

 Contributed Technical Papers, Katmai Series, No. 2). This series has been 

 continued this year by the appearance, also from the press of the National 

 Geographic Society, of "The origin and mode of emplacement of the great 

 tuff deposit in the Valley of Ten Thousand Smokes," by Clarence N. Fenner. 



