RESESS 2008

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SOARS & RESESS protégés 2008.
Kneeling (L to R): Talea L. Mayo, Ramiro Mata, Lumari Pardo-Rodriguez, Alisha R. Fernández, Karen Diaz, Eowyn Connolly-Brown, Luna M. Rodriguez-Manzanet
Front Row (L to R): Cecille M. Villanueva-Birriel, Dana Pauzauskie, Sandra L. Diaz, Roque V. Cespedes, Miriam E. Garcia, Zi Zi Searles, Marques Cameron, Alex O. Gonzalez, Cynthia Boshell, Katherine F. Fornash, Yexary Rodriguez, Ian C. Colón-Pagán
Back Row (L to R): Marcus D.Walter, Emanuelle A. Feliciano-Bonilla, Karl C.Clarke, Isaiah I.Corley, Stephen Hernandez, Christopher Williams, Lennox Thompson, McArthur Jones, Jr., Chahta N.Tahchawwickah
Not pictured: Ezer Patlan

Nine RESESS protégés applied themselves for ten weeks to a broad array of geoscience research topics in 2008. Read their abstracts below.

RESESS operates in partnership with the well-established SOARS (Significant Opportunities in Atmospheric Research and Science) internship program at UCAR (University Corporation for Atmospheric Research). In 2008, protégés participated in a SOARS-sponsored leadership orientation, team-building exercises, seminars, and writing workshops. These students form a core learning community from which they draw upon for peer support and shared experiences. RESESS aims to strengthen the presence of underrepresented groups within the solid earth sciences and increase the completion of master's and PhD degrees by these groups in the field.

2008 Earth, Wind, Sea, and Sky: RESESS and SOARS Protégé Abracts

Cynthia Boshell

Uplift, subsidence, or systematic error? Measuring elevation in the Longmont-Denver corridor

The Colorado Department of Transportation (CDOT) and National Geodetic Survey (NGS) conducted a 119 km leveling project that extended from Longmont to Denver International Airport. Up to10 cm elevation differences were observed in the area of Denver International Airport, raising questions about data collection procedures and benchmark stability. A detailed examination of data was conducted to identify possible systematic error. Field notes and the field abstract (a report that summarized recorded observations) were examined to determine how observations were made. Observation times, progression of observation activities, and time lapses between observations were identified as the main sources of systematic error. Data analysis was performed using elevation differences, published values, and loop closures. These provided further evidence that elevation differences were the result of systematic error. This research concluded that systematic error was responsible for the overall observed elevation difference of approximately10 cm and provided a basis for the National Geodetic Survey to finalize and publish elevation data for the benchmarks included in this leveling project. Future impacts of this research will include improvements in field crew training, revised data analysis procedures, and continued monitoring of possible uplift and subsidence through the National Geodetic Survey’s Height Modernization program.

Isaiah I. Corley

Modeling rainfall thresholds for landslide analysis

This research intends to successfully analyze landslide behavior by using a deterministic analysis of rainfall thresholds. An alternative approach for defining rainfall thresholds uses deterministic models for rainfall infiltration and slope stability testing. Deterministic modeling is believed to be less computationally costly than the empirical method. This project aims to define rainfall thresholds in Western Oregon by applying the deterministic modeling technique. The objectives are to use a computer model of landslide initiation and rainfall infiltration to define rainfall thresholds for certain sites in Western Oregon and to compare these thresholds with historically collected rainfall threshold and rainfall amounts data.

The project can be divided into subcategories: define landslide provinces based on similar climate, terrain, and geology; compile a database of relevant geotechnical parameters for selected provinces; model rain infiltration and slope stability for representative rainfall intensities and durations, geotechnical parameters, soil thicknesses, and slope angles for selected provinces; define thresholds based on model results; and compare rainfall thresholds defined by computer modeling with published empirically defined thresholds and actual landslide events. Two areas of major research are discussed: the rainfall threshold analysis methods, and how they can be used by the TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis) program to compute a factor of safety.

Emanuelle A. Feliciano Bonilla

Terrestrial laser scanning study of gully erosion at West Bijou Creek, Arapahoe County, Colorado: An investigation on field acquisition and data processing

Terrestrial laser scanning (TLS) or ground-based LiDAR (light detection and ranging) is a relatively new technology that digitally maps geological outcrops at centimeter-to-millimeter resolutions. This paper reports the results of a trial TLS project that has two main aims: collecting scans for monitoring gully erosion, and conducting a survey to connect field methods of TLS with geomorphology. The site of this TLS survey was located in Arapahoe County, Colorado, and data collection consisted of a three-day campaign. This project focused on a new approach to analyzing and measuring deformation and erosion in gully-dominated landscapes. Our approach to the survey consisted of going to the field with an Optech scanner to acquire the data, searching for different field acquisition strategies, practicing with data processing, and making a web page of the project for the scientific community. A preliminary terrain model was made in Polyworks software using only 20 percent of the scans; this provided insight into how the landscape model can look in the future. The long-term goal of this research is to keep track of the changes in the morphology of the gullies located at West Bijou Creek in Colorado using Real Time Kinematic GPS (RTK-GPS) and Terrestrial Laser Scanning (TLS). Because applications of TLS in geology and geophysics are evolving rapidly, in this project a web page including a forum is provided to the scientific community with a summary of current field acquisition practices for sharing ideas and discoveries.

Katherine Faye Fornash

Reassessing spatial, temporal, and compositional trends in western North American magmatism using NAVDAT

Plate tectonic setting and magmatic activity are intimately related, as evidenced by the fact that 95% of all magma generation (by volume) occurs along active continental margins. However, in Cenozoic western North America, magmatism occurred more than1,000 km from the active continental margin, even after corrections for Basin and Range extension. Previous research suggests that these magmas may be the product of changing plate configurations between the Farallon and North American plate and subductionrelated processes.

These hypotheses were re-examined using MATLAB-generated animations and visualizations of data in the North American Volcanic and Intrusive Rock Database (NAVDAT, navdat.kgs.ku.edu). Continental basaltic rocks (ages: 80 m.y.-present, SiO2 wt.%: 40-52%, 7,987 samples) and volcanic rocks from four mid-Tertiary volcanic fields (ages: 50 m.y.-20 m.y., SiO2 wt.%: 0-100%, 3,639 samples) were examined for the presence of a subduction-related geochemical signature.

Animations of the temporal and spatial changes in the Na/K ratio of basaltic rocks showed an increase in the prevalence of sodic magmatism through time, as well as a general concentration of more potassic rocks toward the interior of the continent. Also notable was the observation that potassic volcanism in the Sierra Nevadas (~3.5 m.y.) thought to be related to the lithospheric delamination, was the only location of potassic volcanism in the entire western United States province during that time period.

Harker variation diagrams of various major and trace element abundances in the mid-Tertiary volcanic fields revealed that the Trans-Pecos volcanic field had a consistently distinct chemical composition, characterized by low Ba/Nb, Th/Nb, and Sr/Ta ratios, low wt.% CaO and wt.% MgO, and high wt.% TiO2. Differences between the Challis/Absaroka, Mogollon-Datil, and San Juan volcanic fields were subtle but still evident. Taken together, these observations suggest that (1) spatial variations in the intensity of metasomatism of the mantle might have existed at the time, and that (2) magmas in the Trans-Pecos volcanic field may have been generated in a back-arc basin environment.

2008 RESESS protégé Miriam Garcia

Miriam Garcia

Mogi model application on Grímsvötn Volcano, Iceland: continuous GPS data (2004-2008)

Grímsvötn is a subglacial volcano in Iceland with the highest eruption frequency of any of Iceland’s 30 volcanic systems during the past 800 years. It is located below the Vatnajökull ice cap and above the Iceland mantle plume. This study focused on the analysis of Grímsvötn’s recent deformation that will allow a better understanding of its behavior. This insight might also be applicable to the assessment of the risk of volcanic hazards, such as glacial floods (jökulhlaups), that affect the local population. The 2004-2008 time series data from the continuous GPS station (GFUM) was divided into five events. A Mogi model for each event was used to find characteristics of an equivalent point source that results in the same 3-D displacements displayed by GFUM. The Mogi code consists of four parameters: source geometry, observation point, and the Poisson’s ratio and shear modulus of the surrounding crust. Three values are output by the code: displacements, strains, and stresses in the east, north, and up directions. All five recent volcanic events at Grímsvötn were fitted to a volume change at a specific depth using the displacement output. The November 2004 eruption (event 2) resulted in a volume decrease of 23.5E-3 km3 at a depth of 2.55 km. All events had similar model results with the exception of event 4, which had a deep source,15.2 km. There were several aspects of the modeling process that contributed to errors in the results: 1) a non-spherical magma source, 2) an inhomogeneous crust, 3) lack of continuous GPS data at GFUM.

2008 RESESS protégé Stephen Hernandez

Stephen Hernandez

Lineament Analysis for the McMurdo Dry Valleys region, Antarctica

Light Detection and Ranging (LiDAR) data were collected for regions spanning approximately 4,000 km2 in the McMurdo Dry Valleys region of Antarctica. We assess the efficacy of using digital elevation models (DEMs) derived from these data for geomorphic mapping applications in the Dry Valleys. Using the ArcGIS Geographic Information Systems (GIS) software suite, we determine optimal image processing techniques to enhance visibility of geologically and geomorphically significant lineaments including faults, dikes, paleoshorelines, and other rift and glacial features. Optimized filters, shadowing parameters, and the determination of positive and negative relief are applied to regions of interest. Results highlight features that can be used to constrain long-term glacial isostatic adjustment and neotectonic processes related to the West Antarctic Rift System (WARS).

Ezer Patlan

Drilling induced Fracture (DIF) characterization and stress pattern analysis of the Southern McMurdo Sound (SMS) Core, Victoria Land Basin, Antarctica

There is a significant lack of data about present-day stress fields in Antarctica. Stresses provide valuable information about the forces acting on tectonic plates. In Antarctica, stresses may be related to ridge forces such as rifting and/or uplifting, to ice loading/unloading-related processes, or both. This project studies drilling induced fractures from core recovered in the Victoria Land rift basin of Antarctica. Drilling induced fractures form ahead of the drill bit during drilling from stress imbalances due to the removal of excess weight pressure around the rock. Because horizontal stresses strike parallel to the planes made by drilling induced fractures, they can be used to measure modern-day stress fields. Whole core images obtained during core logging by digitally scanning the outside of the core are stitched into longer intact intervals. Drilling induced fractures in the core are ‘picked’ to obtain their azimuth. Magnetically oriented acoustic images of the inside of the drill hole are then compared side by side with the stitched whole core images and visually scanned for matching features. Once the same set of fractures is found in the core and the borehole, it is then possible to rotate core images to match the orientation of the borehole image. This will produce a core image with all the fractures in that interval re-oriented to true north. This final orientation of drilling induced fractures in the core will thus provide the direction of maximum horizontal compressional stress in this area.

2008 RESESS protégé Yexary Rodriguez.

Yexary Rodriguez

Probabilistic analysis of rainfall thresholds for Western Oregon

In western Oregon, many rainfall thresholds have not been analyzed systematically. As a result, landslide prediction is uncertain. This project examined rainfall thresholds throughout western Oregon to estimate the percentage of threshold exceedance events that will produce landslides. For this study, the geologic characteristics, precipitation data, and historical events of western Oregon were collected and analyzed. After filtering the data, we compared the results of the threshold exceedances with landslide occurrences to test the accuracy of the predictions made by the thresholds. Landslides were found to occur both when the threshold was exceeded and also when it was not exceeded. Since rainfall data and landslide data have an incomplete record, only preliminary threshold values were determined. More extensive analysis of the rainfall data and landslide events needs to be performed to determine rainfall threshold values for western Oregon.

2008 RESESS protégé Lennox E. Thompson.

Lennox E. Thompson

Seismic Investigation of the Southern Rio Grande Rift

An upwelling of basaltic magma 29 million years ago caused the earth’s crust to spread apart and create a region known today as the Rio Grande Rift (RGR). The RGR extends from central Colorado through New Mexico to northern Mexico near El Paso. The RGR has different geologic features that distinguish it from most other valleys (e.g., RGR was not cut by a river nor does a river branch upstream). A growing body of evidence shows that geologic activity still occurs in the RGR, with a continuation of faulting, seismicity, and widening at a small rate. This research focuses on the Southern Rio Grande Rift (SRGR) to develop a contour map of velocity structures and moho depth using data from seismograms that have been installed around the region. The topographic mapping, Vp/Vs ratio, and the crustal thickness of the SRGR will define the crustal structure and the tectonic evolution of the region. The results will assist in understanding the crustal structure of not only the SRGR, but the RGR in general. Results have been obtained for the SRGR using Generic Mapping Tool which includes a contour plot of the Vp/Vs ratio and crustal thickness in that region.

Students interested in applying for the 2008 RESESS program should submit an application before February 1, 2008. The application form is available at (http://resess.unavco.org/application/application.html).

Photo credits: Carlye Calvin of UCAR Communications.