Geology topics

R. Wagner

Publications and source records attributed to R. Wagner.

5 recordsLinked to original sources

USGS2011

Linking middle-school teachers to Earthscope

EarthScope is a multidisciplinary geophysical investigation of the structure and deformation of the North American continent. Components include a transportable array of digital seismometers (USArray) that will image the continental crust and underlying mantle, and Global Positioning System (GPS) receivers and strainmeters (Plate Boundary Observatory, PBO) that will measure tectonic and volcanic deformations Translating geophysics for kindergarten through 12th grade (K‐12) teachers and their students involves inviting them to explore new understandings of how Earth works. When they construct their understanding of Earth science through geophysical problem solving, these learners can engage in Earth‐Scope, which offers unprecedented public access to data from seismology and geodesy.

Eos, Transactions, American Geophysical Union↗

USGS2008

Distribution of icy particles across Enceladus' surface as derived from Cassini-VIMS measurements

The surface of Enceladus consists almost completely of water ice. As the band depths of water ice absorptions are sensitive to the size of particles, absorptions can be used to map variations of icy particles across the surface. The Visual and Infrared Mapping Spectrometer (VIMS) observed Enceladus with a high spatial resolution during three Cassini flybys in 2005 (orbits EN 003, EN 004 and EN 011). Based on these data we measured the band depths of water ice absorptions at 1.04, 1.25, 1.5, and 2 μm. These band depths were compared to water ice models that represent theoretically calculated reflectance spectra for a range of particle diameters between 2 μm and 1 mm. The agreement between the experimental (VIMS) and model values supports the assumption that pure water ice characterizes the surface of Enceladus and therefore that variations in band depth correspond to variations in water ice particle diameters. Our measurements show that the particle diameter of water ice increases toward younger tectonically altered surface units with the largest particles exposed in relatively "fresh" surface material. The smallest particles were generally found in old densely cratered terrains. The largest particles (~0.2 mm) are concentrated in the so called “tiger stripes” at the south pole. In general, the particle diameters are strongly correlated with geologic features and surface ages, indicating a stratigraphic evolution of the surface that is caused by cryovolcanic resurfacing and impact gardening.

Icarus↗

USGS2008

Fluvial erosion and post-erosional processes on Titan

The surface of Titan has been revealed by Cassini observations in the infrared and radar wavelength ranges as well as locally by the Huygens lander instruments. Sand seas, recently discovered lakes, distinct landscapes and dendritic erosion patterns indicate dynamic surface processes. This study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas. Fluvial erosion channels on Titan as identified at the Huygens landing site and in RADAR and Visible and Infrared Mapping Spectrometer (VIMS) observations have been compared to analogous channel widths on Earth yielding average discharges of up to 1600 m3/s for short recurrence intervals that are sufficient to move centimeter-sized sediment and significantly higher discharges for long intervals. With respect to the associated drainage areas, this roughly translates to 1-150 cm/day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0.6-60 mm/h rainfall rates. Thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment. During Cassini's T20 fly-by, the VIMS observed an extremely eroded area at 30?? W, 7?? S with resolutions of up to 500 m/pixel that extends over thousands of square kilometers. The spectral characteristics of this area change systematically, reflecting continuous compositional and/or particle size variations indicative of transported sediment settling out while flow capacities cease. To account for the estimated runoff production and widespread alluvial deposits of fine-grained material, release of area-dependent large fluid volumes are required. Only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features. ?? 2008 Elsevier Inc.

Icarus↗

USGS2005

Ecology and shell chemistry of Loxoconcha matagordensis

Studies of the seasonal ecology and shell chemistry of the ostracode Loxoconcha matagordensis and related species of Loxoconcha from regions off eastern North America reveal that shell size and trace elemental (Mg/Ca ratio) composition are useful in paleothermometry using fossil populations. Seasonal sampling of populations from Chesapeake Bay, augmented by samples from Florida Bay, indicate that shell size is inversely proportional to water temperature and that Mg/Ca ratios are positively correlated with the water temperature in which the adult carapace was secreted. Microprobe analyses of sectioned valves reveal intra-shell variability in Mg/Ca ratios but this does not strongly influence the utility of whole shell Mg/Ca analyses for paleoclimate application.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS1994

Galileo Photometry of Asteroid 951 Gaspra

Galileo images of Gaspra make it possible for the first time to determine a main-belt asteroid's photometric properties accurately by providing surface-resolved coverage over a wide range of incidence and emission angles and by extending the phase angle coverage to phases not observable from Earth. We combine Earth-based telescopic photometry over phase angles 2° ≤ α ≤ 25° with Galileo whole-disk and disk-resolved data at 33° ≤ α ≤ 51° to derive average global photometric properties in terms of Hapke's photometric model. The microscopic texture and particle phase-function behavior of Gaspra's surface are remarkably like those of other airless rocky bodies such as the Moon. The macroscopic surface roughness parameter, θ̄ = 29°, is slightly larger than that reported for typical lunar materials. The particle single scattering albedo, ώ 0 = 0.36 ± 0.07, is significantly larger than for lunar materials, and the opposition surge amplitude, B 0 = 1.63 ± 0.07, is correspondingly smaller. We determine a visual geometric albedo p v = 0.22 ± 0.06 for Gaspra, in close agreement with p v = 0.22 ± 0.03 estimated from Earth-based observations. Gaspra's phase integral is 0.47, and the bolometric Bond albedo is estimated to be 0.12 ± 0.03. An albedo map derived by correcting Galileo images with our average global photometric function reveals subdued albedo contrasts of ±10% or less over Gaspra's northern hemisphere. Several independent classification algorithms confirm the subtle spectral heterogeneity reported earlier (S. Mottola, M. DiMartino, M. Gonano-Beurer, H. Hoffman, and G. Neukum, 1993, Asteroids, Comets, Meteors, pp. 421-424; M. J. S. Belton et al ., 1992, Science 257, 1647-1652). Whole-disk colors (0.41 ≤ λ ≤ 0.99 μm) vary systematically with longitude by about ±5%, but color differences as large as 30% occur locally. Colors vary continuously between end-member materials whose areal distribution correlates with regional topography. Infrared: violet (0.99:0.41-μm) color ratios on Gaspra are strongly correlated with local elevation, being largest at lower elevations and smaller at higher elevations. No correlation was detected between elevation and the green:violet (0.56:0.41-μm) color ratio. Bright materials with a strong 1-μm absorption occur primarily in association with craters along ridges, while darker materials with 30% weaker 1-μm signatures occur downslope. The variations of color and albedo cannot be easily explained by grain-size effects alone or by differences in photometric geometry. The trends observed are consistent with those revealed by laboratory studies of the effects of comminution, glass formation, and segregation of metal from silicate components in chondritic meteorites and also in some silicate mixtures. The relative importance of these various processes on Gaspra remains to be determined.

Icarus↗