Geological map of the Glenns Ferry-Hagerman area, west-central Snake River Plain, Idaho
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Geology topics
H. A. Powers
Publications and source records attributed to H. A. Powers.
A further contribution to the petrology of Haleakala volcano, Hawaii
Sixteen new chemical analyses of the later rocks of Haleakala Volcano , on the island of Maui, Hawaii , add to the differentiation picture for that volcano . The early rocks of the volcano are tholeiitic. These are followed by dominant hawaiites with less abundant alkalic olivine basalts, picrite-basalts of ankaramite type, and a few mugearites. Still later rocks, separated from earlier ones by a profound erosional unconformity, include some hawaiites and ankaramites, but are dominantly alkalic olivine basalts (basanitoids) containing as much as 16.5 percent normative nepheline, some of them transitional to ankaramite. The progression toward ultramafic, strongly undersaturated rocks (nephelinites), characteristic of the post-erosional lavas of other Hawaiian volcanoes, appears to have just begun at Haleakala .
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Volcanic ash from Mount Mazama (Crater Lake) and from Glacier Peak
New petrographic and chemical data indicate that the great Mount Mazama eruption at Crater Lake, Oregon, about 6600 years ago was the source of most ash which has been called "Glacier Peak" and of some ash called "Galata." Glacier Peak volcano in Washington was itself the source of an older ash deposit, perhaps very late glacial or early postglacial in age.
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Composition and origin of basaltic magma of the Hawaiian Islands
Silica-saturated basaltic magma is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This magma may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma. Silica-deficient basaltic magma, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of magma are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable magma under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components.
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Contribution to the petrography of Haleakala Volcano, Hawaii
The volcanic rocks of Haleakala Volcano comprise, from oldest to youngest, the Honomanu, Kula, and Hana volcanic series. The Honomanu volcanic series consists largely of olivine basalt, with less abundant basalt and picrite-basalt containing large phenocrysts of olivine. In the Kula and Hana volcanic series there are some basalts and olivine basalts, but the characteristic rocks are andesites and picrite-basalt containing abundant phenocrysts of augite as well as olivine. New chemical analyses of six specimens of Kula lavas are given. Five are andesites, and one a picrite-basalt. Each of the six rocks is described in detail. A variation diagram for Haleakala rocks illustrates the alkalic character of the series.
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