ABSTRACT Infrared and high contrast panoramic photographs of Devonian nonmarine sedimentary rocks exposed along the Catskill Front, southeastern New York, reveal details of sandstone body continuity. The laterally persistent Kaaterskill sandstones in the upper part of the sequence may mark a transition from meandering stream to braided stream deposition.

10.1306/74d71965-2b21-11d7-8648000102c1865d

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Decameter-scale pedestal craters in the tropics of Mars: Evidence for the recent presence of very young regional ice deposits in Tharsis

Earth and Planetary Science Letters (2011)

S. C. Schon J. W. Head

Tharsis

Pedestal

10.1016/j.epsl.2011.09.005

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Citations (13)

Fortuna Tessera, Venus: Evidence of horizontal convergence and crustal thickening

Geophysical Research Letters (1989)

Richard W. Vorder Bruegge J. W. Head

Structural and tectonic patterns mapped in Fortuna Tessera are interpreted to reflect a change in the style and intensity of deformation from east to west, beginning with simple tessera terrain at relatively low topographic elevations in the east and progressing through increasingly complex deformation patterns and higher topography to Maxwell Montes in the west. These morphologic and topographic patterns are consistent with east‐to‐west convergence and compression and the increasing elevations are interpreted to be due to crustal thickening processes associated with the convergent deformational environment. Using an Airy isostatic model, crustal thicknesses of approximately 35 km for the initial tessera terrain, and crustal thicknesses of over 100 km for the Maxwell Montes region are predicted. Detailed mapping with Magellan data will permit the deconvolution of individual components and structures in this terrain.

Isostasy

10.1029/gl016i007p00699

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Citations (44)

North‐south roughness anisotropy on Venus from the Magellan Radar Altimeter: Correlation with geology

Journal of Geophysical Research Atmospheres (2006)

Н. В. Бондаренко M. A. Kreslavsky J. W. Head

Analysis of the Doppler spectrum of Magellan Radar Altimeter echoes has revealed the spatially coherent deflection of the echo center from the nadir point (Tyler et al., 1992). We present and analyze a global map of the Doppler centroid of the radar altimeter echo, which, for the plains of Venus, characterizes the degree of anisotropy of the surface roughness in the north–south direction at scales from decimeters to kilometers. We found a global hemispherical trend of roughness anisotropy: on average, equator‐facing slopes are steeper than pole‐facing slopes. We searched globally for correlations between contrasts in roughness anisotropy and surface geology. We found that sharp contrasts in anisotropy often coincide with boundaries of geological units, although not consistently. We found a number of examples where radar‐bright (rough) lava flows have higher asymmetry than their surroundings. Diffuse radar‐dark crater‐related parabolic features and halos often have a symmetric roughness signature, while typical regional plains away from these diffuse features often have an anisotropic roughness. There is not, however, any direct and uniform correlation between the roughness anisotropy signature and geomorphologic terrain type or appearance in the radar images. We believe that asymmetric topography of deposits of windblown material, e.g., microdunes or small‐scale wind streaks in the wind shadow of obstacles, is the main contributor to the observed roughness anisotropy.

10.1029/2005je002599

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Citations (18)

Uses of volcanic eruption processes as probes of the structure of planetary crusts.

Geophysical Journal International (1982)

L. Wilson J. W. Head

Vulcanian eruption

Volcanology

Source

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Impact ejecta-induced melting of surface ice deposits on Mars

Icarus (2016)

D. K. Weiss J. W. Head

Regolith

Meltwater

Bedrock

10.1016/j.icarus.2016.07.007

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Citations (17)

Accelerated thermokarst formation in the McMurdo Dry Valleys, Antarctica

Scientific Reports (2013)

J. S. Levy Andrew G. Fountain J. L. Dickson J. W. Head Marianne Okal

Thermokarst is a land surface lowered and disrupted by melting ground ice. Thermokarst is a major driver of landscape change in the Arctic, but has been considered to be a minor process in Antarctica. Here, we use ground-based and airborne LiDAR coupled with timelapse imaging and meteorological data to show that 1) thermokarst formation has accelerated in Garwood Valley, Antarctica; 2) the rate of thermokarst erosion is presently ~ 10 times the average Holocene rate; and 3) the increased rate of thermokarst formation is driven most strongly by increasing insolation and sediment/albedo feedbacks. This suggests that sediment enhancement of insolation-driven melting may act similarly to expected increases in Antarctic air temperature (presently occurring along the Antarctic Peninsula) and may serve as a leading indicator of imminent landscape change in Antarctica that will generate thermokarst landforms similar to those in Arctic periglacial terrains.

Thermokarst

Landform

10.1038/srep02269

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Citations (44)

The Geology of Gaspra

Icarus (1994)

M. H. Carr R. Kirk A. S. McEwen J. Veverka P. C. Thomas

The surface of Gaspra can be divided into several facets separated by ridges. Superimposed on the facets and ridges are two populations of craters. Type 1 craters are crisply defined and constitute a production function of impact origin. Type 2 craters are mostly irregular shallow depressions and probably of various origins. Some of the type 2 craters may have formed by impact and be remnants of a crater population that predates the type 1 population. The number of type 1 craters suggests that they started to accumulate 2 × 107 to 3 × 108 years ago. The freshest craters have a depth/diameter ratio of 1:7, as compared with 1:5 typically observed on other bodies. The craters appear to have become shallower with age at a rate of 10-6 to 10-7 m/year. The shallow depth of newly formed craters and the progressive degradation with age are ascribed to downslope movement of poorly coherent surface materials, the movement being aided by seismic shaking as a result of impact. The surface shows subtle color differences. The most prominent differences are observed around craters on ridges, where the surface has a stronger 1-μm absorption than elsewhere. The contrast is not observed around craters on the facets. The color differences are attributed to alteration of the materials brought to the surface. The unaltered material is estimated to be located at least 50 m below the surface on the facets. Only on the ridges is unaltered material at a shallow enough depth to be excavated by the observed craters. The rate of degradation of craters, the rounded form of the ridges, the depth of altered material on the facets, and the presence of old degraded craters all suggest that Gaspra is covered with a regolith a few tens to several tens of meters thick.

10.1006/icar.1994.1006

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Citations (95)