Geoprocessing Techniques for the Visualization of Subsurface Geologic Data in Geographic Information Systems

ABSTRACT The ability to visualize subsurface geologic information is critical to sound decision making in many disciplines of geology. While there are numerous commercial off-the-shelf software solutions available to model geologic data in both 2D and 3D, these can be costly and have a steep learning curve. Some of the same functionality of these software packages can be accomplished by workflows that incorporate built-in geoprocessing tools of Geographic Information System (GIS) software. These workflows allow the geologist to plot vertical or inclined borehole data in 2D or 3D, create section views of raster data along section lines, and provide a means to convert contact elevations from existing geologic cross sections into plan-view or 3D space. These workflows have been successfully used to visualize construction data and subsurface geologic information for several embankment dams. Grouting and exploratory borehole data from databases with tens of thousands of records have been transformed into 2D and 3D GIS features. The workflows were instrumental in developing a 3D GIS model of site geology from which a series of geologic cross sections were drawn. These sections were critical in informing risk decisions related to the foundation conditions for a recent risk assessment of an earthen embankment dam.

Using Google Earth and Google Street View To Rate Rock Slope Hazards

Rockfall hazard from cut slopes along highways are caused primarily by unfavorable orientations of discontinuities, presence of unconsolidated cobble/boulder deposits, undercutting of strong rocks by weaker rocks, or degradation of weak rock masses. The rockfall hazard rating system (RHRS) was introduced in Oregon to evaluate the hazard and associated risk to an adjacent transportation facility for a cut slope's potential for releasing rockfalls. RHRS is a numerical score–based rating of parameters that characterize rockfalls. The parameters include slope geometry (height, angle, roughness, orientation), geologic information (discontinuity characterization, undercutting susceptibility), driver's line of sight, and climate. Geologic information, such as discontinuity orientation data, is traditionally collected using a transit compass and measuring tape at the site. The method is time consuming and expensive and can be dangerous. This study tests the use of Google Earth and Google Street View tools to remotely collect data for selected parameters that characterize rockfall hazard. The selected parameters are categorized under slope profile, geologic characteristics, and impact factor parameters, which are quantitatively and qualitatively measurable using Google Street View and Google Earth. A section of U.S. 33 with a high density of road cuts and two more sites along Interstate 64, all located in Virginia, were selected for the study. Sites were evaluated by using a combination of measurement tools available in Google Earth and a visual inspection of the rock units in Google Street View. The results of seven of the sites were re-evaluated using field-derived data.

Austrian versus Hungarian bauxites in an Alpine tectonic context: a tribute to Prof. Andrea Mindszenty

The correlation between the Cretaceous bauxites of Austria and Hungary was first highlighted by the pioneering work of Andrea Mindszenty in the 1980s. The physical distance today between these bauxite occurrences, located in the Northern Calcareous Alps and the Transdanubian Central Range, is on the order of hundred of kilometers. However, a semi-quantitative palinspastic reconstruction of their relative positions at the time of bauxite deposition during the Late Cretaceous (Turonian to early Santonian) shows their much closer proximity. Still, the important differences between these Upper Cretaceous bauxites are due to their different paleogeographic settings during their deposition on a subaerially exposed Eo-Alpine nappe substratum. Some other differences, such as porosity, are attributed to the subsequent tectonic overprint in the Alpine edifice. The Austrian and Hungarian bauxites not only record important information about of the syn-depositional geologic landscape but also provide clues about the pre- and post-depositional regional tectonic context of the areas where they developed. The typical setting for many of the Cretaceous bauxites in the broader Alpine region was uplift and karstification associated with the formation of various flexural basin systems. Therefore bauxites, in general, may contain important geologic information about the regional geodynamic processes, as it was pointed by Andrea Mindszenty, in a pioneering manner, already in the early 1990s.

A RESPONSE TO THE COMMENTARY BY KAREN OLSEN BRUHNS, WILLIAM E. BROOKS, AND DEBORAH TRUHAN ON “ECUADORIAN CINNABAR AND THE PREHISPANIC TRADE IN VERMILION PIGMENT: VIABLE HYPOTHESIS OR RED HERRING?”

Our LAQ paper concluded that cinnabar pigment found by archaeologists in northern Peru was produced at Huancavelica in south-central Peru. In contrast, Bruhns and her colleagues suggest the mines near Azogues in southern Ecuador were an important cinnabar source for prehispanic Ecuador and Peru. In their commentary, they introduce new historic and geologic information to support their view, but a critical analysis demonstrates that it does not undermine our conclusions.