Mladen M. Dordevic

MaRGEE: Move and Rotate Google Earth Elements

Abstract Google Earth is recognized as a highly effective visualization tool for geospatial information. However, there remain serious limitations that have hindered its acceptance as a tool for research and education in the geosciences. One significant limitation is the inability to translate or rotate geometrical elements on the Google Earth virtual globe. Here we present a new JavaScript web application to “Move and Rotate Google Earth Elements” (MaRGEE). MaRGEE includes tools to simplify, translate, and rotate elements, add intermediate steps to a transposition, and batch process multiple transpositions. The transposition algorithm uses spherical geometry calculations, such as the haversine formula, to accurately reposition groups of points, paths, and polygons on the Google Earth globe without distortion. Due to the imminent deprecation of the Google Earth API and browser plugin, MaRGEE uses a Google Maps interface to facilitate and illustrate the transpositions. However, the inherent spatial distortions that result from the Google Maps Web Mercator projection are not apparent once the transposed elements are saved as a KML file and opened in Google Earth. Potential applications of the MaRGEE toolkit include tectonic reconstructions, the movements of glaciers or thrust sheets, and time-based animations of other large- and small-scale geologic processes.

Exploring the reasons for the seasons using Google Earth, 3D models, and plots

ABSTRACT Public understanding of climate and climate change is of broad societal importance. However, misconceptions regarding reasons for the seasons abound amongst students, teachers, and the public, many of whom believe that seasonality is caused by large variations in Earth’s distance from the Sun. Misconceptions may be reinforced by textbook illustrations that exaggerate eccentricity or show an inclined view of Earth’s near-circular orbit. Textbook explanations that omit multiple factors influencing seasons, that do not mesh with students’ experiences, or that are erroneous, hinder scientifically valid reasoning. Studies show that many teachers share their students’ misconceptions, and even when they understand basic concepts, teachers may fail to appreciate the range of factors contributing to seasonal change, or their relative importance. We have therefore developed a learning resource using Google Earth, a virtual globe with other useful, weather- and climate-related visualizations. A classroom test of 27 undergraduates in a public research university showed that 15 improved their test scores after the Google Earth-based laboratory class, whereas 5 disimproved. Mean correct answers rose from 4.7/10 to 6/10, giving a paired t-test value of 0.21. After using Google Earth, students are helped to segue to a heliocentric view.

Dynamics of plume–triple junction interaction: Results from a series of three‐dimensional numerical models and implications for the formation of oceanic plateaus

Mantle plumes rising in the vicinity of mid-ocean ridges often generate anomalies in melt production and seafloor depth. This study investigates the dynamical interactions between a mantle plume and a ridge-ridge-ridge triple junction, using a parameter space approach and a suite of steady state, three-dimensional finite element numerical models. The top domain boundary is composed of three diverging plates, with each assigned half-spreading rates with respect to a fixed triple junction point. The bottom boundary is kept at a constant temperature of 1350°C except where a two-dimensional, Gaussian-shaped thermal anomaly simulating a plume is imposed. Models vary plume diameter, plume location, the viscosity contrast between plume and ambient mantle material, and the use of dehydration rheology in calculating viscosity. Importantly, the model results quantify how plume-related anomalies in mantle temperature pattern, seafloor depth, and crustal thickness depend on the specific set of parameters. To provide an example, one way of assessing the effect of conduit position is to calculate normalized area, defined to be the spatial dispersion of a given plume at specific depth (here selected to be 50 km) divided by the area occupied by the same plume when it is located under the triple junction. For one particular case modeled where the plume is centered in an intraplate position 100 km from the triple junction, normalized area is just 55%. Overall, these models provide a framework for better understanding plateau formation at triple junctions in the natural setting and a tool for constraining subsurface geodynamical processes and plume properties.

Emergent and animated COLLADA models of the Tonga Trench and Samoa Archipelago: Implications for geoscience modeling, education, and research

We report on a project aimed at developing emergent animated COLLADA (collaborative design activity) models of the Tonga-Samoa region of the western Pacific for teaching and outreach use with Google Earth. This is an area of historical importance to the development of plate tectonic theory and is important today owing to neotectonic activity, including a 29 September 2009 tsunamigenic earthquake. We created three types of models: an emergent digital elevation model of the Tonga slab with associated magmatic arc and backarc basin based on GeoMapApp (Marine Geoscience Data System, Lamont-Doherty Earth Observatory) data mining; animated models of alternative plate tectonic scenarios; and a large-scale model that permits users to view the subsurface down to lower mantle levels. Our models have been deployed in non-science major laboratory classes, and positive learning outcomes were documented in an independent study by S. Wild and J. Gobert. The models have also been made available to colleagues and the public via the Old Dominion University Pretlow Planetarium and an outreach and dissemination website (http://www.digitalplanet.org). In the process of constructing a complete set of tectonic models for the area of interest, we added cases that have not been described in the research literature. Thus, this study spans the three functions of modern academia, i.e., research, teaching, and outreach, and the multifaceted aspects of creating, using, testing, and disseminating electronic geospatial learning resources.