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David J. Roddy

Publications and source records attributed to David J. Roddy.

4 recordsLinked to original sources
USGS2012

Numerical simulations of the Shoemaker-Levy 9 impact plumes and clouds: A progress report

Preliminary 2D/3D numerical simulations were carried out for the penetration of 1-km bodies in the Jovian atmosphere and the subsequent rise and collapse of the erupted plumes. A body that crushed at a stagnation point pressure of 5 kbar produced a plume that rose to 800 km. Evolution of the shape of the calculated plume corresponds rather well to the plumes observed by HST. A crescent-shaped lobe centered on the “backfire” azimuth was produced by lateral flow during plume collapse. The plumes observed on Jupiter rose about 4 times higher, and their rise and fall times were about twice those in this calculation. Plume height is a sensitive function of the distribution of energy along the entry path; a very low-strength body will disintegrate higher along the penetration path and will produce a higher plume.

Geophysical Research Letters↗
USGS1992

Preliminary results of the U.S. Geological Survey-Iowa Department of Natural Resources Geological Survey Bureau Manson Core Drilling Project

The U.S. Geological Survey and Iowa Department of Natural Resources Geological Survey Bureau completed, in 1992, a two-year core drilling program in the Manson Impact Structure, a 35-km-diameter, Cretaceous-Tertiary boundary-age feature located in north-central Iowa. A total of 12 cores sampled in excess of 1,200 m (4,000 ft) of crater rocks, supplementing the two previously drilled shallow cores from the structure. The cores penetrated the three major terranes in the Manson Impact Structure, the terrace terrane, crater moat, and central peak. Preliminary interpretations identified several important impact-related lithologies in these cores. The most widespread is sedimentary clast breccia, a postimpact polymictic breccia or mixtite that mantles at least part of all crater terranes. Two types of crystalline clast breccias were cored on the central peak, one with a melt matrix, the other with a matrix dominated by silt- to sand-sized grains. Large blocks of basement gneiss that formed the interior of the central peak were encountered in several cores. Within the terrace terrane, structurally preserved Cretaceous strata and an overturned ejecta flap of Proterozoic and Paleozoic sedimentary rocks were encountered. Only sedimentary clast breccia was encountered in the crater moat. The preliminary investigation of these cores has provided significant information on the geometry and history of the Manson Impact Structure, but it has also prompted many more questions.

Iowa↗
USGS1980

Map showing the Elko crater field, Elko County, Nevada

The Elko crater field consists of two arrays of rimmed craters in the valleys of Dorsey, Susie, and McClellan Creeks, 30 to 50 km north of Elko, Nevada. In the principal array, more the 165 craters are scattered irregularly in an area 3 km wide and 20 km long. Most of the the craters are circular but some, formed by overlap, are oval or irregular. They range from 5 m to 250 m in diameter and the relief of the largest ones, from the sedimentary floor of the cater to the top of the rim, is at least 6 m. The surficial material of the rims is principally gravel similar to that in the surrounding terrane. The surficial material inside the craters is primarily silt, probably blown in by the wind, and pebbles, apparently washed in from the rims. There is also a later of volcanic ash at a depth of about 2 m. This ash was identified by its physical and mineralogical composition as the Mazama ash (R. E. Wilcox, oral commun., 1976), a ±6600 year old ash bed also present in the alluvium of Dorsey and Susie Creeks. The craters are presently interpreted as having been formed by a meteor shower although no meteor material has been discovered. Investigation is continuing.

Nevada↗