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Dallas L. Peck

Publications and source records attributed to Dallas L. Peck.

14 recordsLinked to original sources
USGS1968

The formation of columnar joints in the upper part of Kilauean lava lakes, Hawaii

Cracks were observed forming at the surface of Makaopuhi lava lake during the March 1965 Kilauea eruption, and were studied by repeated mapping and observations of this lake ; the 1963 Alae lava lake was similarly studied. Cracks open within a minute after molten lava is exposed at the surface, and form either random or oriented orthogonal networks which outline large plates of unjointed crust. Within a few hours, additional cracks subdivide the plates into polygons averaging 15 ft in width. The accumulation of gases trapped beneath the crust near centers of polygons, and the escape of gases from marginal parts, cause upbowing of polygon centers and downsagging of margins. As the crust cools and increases in thickness following stagnation of the lake , existing cracks extend downward and new cracks open. Some new cracks subdivide pre-existing polygons, and short cracks of shallow depth form near polygon centers. Still other cracks apparently open at depths of tens of feet within the crust, propagate upward, and finally feather out near the surface into short cracks which are concentrated in long swarms that cross several polygons. Cracks initiate at temperatures ranging from ambient to about 900°C, and propagate downward into parts of the crust near 1000°C. Cracking results from stresses induced largely by thermal contraction, but also by differential subsidence of the crust. Seismic recordings of shock vibrations due to cracking of Kilauea Iki lava lake indicate a diurnal variation in frequency, with a maximum around midnight and a minimum around noon.

Hawaii↗
USGS1964

Geologic reconnaissance of the Antelope-Ashwood area, north-central Oregon, with emphasis on the John Day Formation of late Oligocene and early Miocene age

This report briefly describes the geology of an area of about 750 square miles in Jefferson, Wasco, Crook, and Wheeler Counties, Oregon. About 16,000 feet of strata that range in age from pre-Tertiary to Quaternary are exposed. These include the following units: pre-Tertiary slate, graywacke, conglomerate, and meta-andesite; Clarno Formation of Eocene age - lava flows, volcanic breccia, tuff, and tuffaceous mudstone, chiefly of andesitic composition; John Day Formation of late Oligocene and early Miocene age - pyroclastic rocks, flows, and domes, chiefly of rhyolitic composition; Columbia River Basalt of middle Miocene age - thick, columnar jointed flows of very fine grained dense dark-gray basalt; Dalles Formation of Pliocene age - bedded tuffaceous sandstone, siltstone, and conglomerate; basalt of Pliocene or Pleistocene age - lava flows of porous-textured olivine basalt; and Quaternary loess, landslide debris, and alluvium. Unconformities separate pre-Tertiary rocks and Clarno Formation, Clarno and John Day Formations, John Day Formation and Columbia River Basalt, and Columbia River Basalt and Dalles Formation. The John Day Formation, the only unit studied in detail, consists of about 4,000 feet of tuff, lapilli tuff, strongly to weakly welded rhyolite ash flows, and less abundant trachyandesite flows and rhyolite flows and domes. The formation was divided into nine mappable members in part of the area, primarily on the basis of distinctive ledge-forming welded ash-flow sheets. Most of the sheets are composed of stony rhyolite containing abundant lithophysae and sparse phenocrysts. One sheet contains 10 to 20 percent phenocrysts, mostly cryptoperthitic soda sanidine, but including less abundant quartz, myrmekitic intergrowths of quartz and sanidine, and oligoclase. The rhyolitic ash flows and lava flows were extruded from nearby vents, in contrast to some of the interbedded air-fall tuff and lapilli tuff of dacitic and andesitic composition that may have been derived from vents in an ancestral Cascade Range. The John Day is dated on the basis of a late Oligocene flora near the base of the formation and early Miocene faunas near the top of the formation. The middle Miocene and older rocks in the Antelope-Ashwood area are broadly folded and broken along northeast-trending faults. Over much of the area the rocks dip gently eastward from the crest of a major fold and are broken along a series of steeply dipping antithetic strike faults. Pliocene and Quaternary strata appear to be undeformed. At the Priday agate deposit, chalcedony-filled spherulites (thunder-eggs) occur in the lower part of a weakly welded rhyolitic ash flow. The so-called thunder-eggs are small spheroidal bodies, about 3 inches in average diameter; each consists of a chalcedonic core surrounded by a shell of welded tuff that is altered to radially oriented fibers of cristobalite and alkalic feldspar.

Oregon↗
USGS1964

Geology of the central and northern parts of the Western Cascade Range in Oregon

This report pt·esents a description of the stratigraphy, structure, and petrology of the volcanic rocks of the central and northern parts of the Western Cascade Range of Oregon. The study is a part of a long-range cooperative program between the U.S. Geological Survey and the Oregon State Department of Geology and Mineral Industries to prepare a geologic map of Oregon. The map area, about 7,500 square miles, lies in the densely forested western slope of the Cascade Range. It is bounded approximately by lat 43° N. and lat 45°30' N. on the south and north, the crest of the range on the east, and long 123° W. and the edge of the Willamette Valley on the west. The geology, which was mapped by reconnaissance methods, is chiefly based on examination of rock exposures along roads. The Cascade Range in Oregon comprises two physiographic divisions: the Western Cascade Range, which includes a wide, deeply dissected belt of volcanic formations making up the western slope of the range, and the High Cascade Range, which includes chiefly younger cones and lava flows forming the nearly undissected crest of the range. The volcanic rocks of the Western Cascade Range are deformed and partially altered flows and pyroclastic rocks that range in age from late Eocene t·o lute Miocene, as determined chiefly from fossil plants from more than 50 localities. These volcanic rocks overlie or interfinger westward with marine sedimentary rocks, and in the southwestern part of the map area they overlie pre-Tertiary plutonic and metamorphic rocks of the Klamath Mountains.

Oregon↗