Mr. Trimble's Research
In addition to teaching, I've worked as a geologist in industry and academia. My research interests include regional tectonics, structural geology, digital terrain modeling, thermochronology, and geochronology. I have conducted earth science research in Oregon, Alaska, Argentina, Wyoming, Georgia, and Arizona.
Geology Research at Oregon State University (2014-2016)
Title: A Refined Structural Model of the Oregon Cascades Arc-Backarc Tectonic Province
Abstract: Extensive new digital fault mapping in the Oregon Cascades and backarc reveals previously unrecognized fault complexity at the full range of spatial and temporal scales. A combination of slope, aspect, curvature, and hillshade raster data calculated from 1 meter lidar bare earth digital models allowed for discovery of new faults and revisions to known faults. When combined with subsets of published fault layers from DOGAMI and the USGS, we present a significantly improved multilayer fault database of the arc backarc tectonic system.
In the High Cascades between Mt Jefferson and the Three Sisters (44°N-45°N), a generation of young NNW trending en echelon fault scarps crosscut exposed volcanic stratigraphy and the youngest glacial valley surfaces, revealing an active cross-arc fault system that potentially connects the Sisters Fault Zone to the Breitenbush fault system. The southeast extension of the fault system apparently connects to young faults cutting the northwest flank of Newberry Caldera. This cross-arc fault system crosscuts the NS trend of the Cascade Graben at Mt Jefferson but does not appear to reactivate the Green Ridge Fault. These NNW-trending faults presently dominate Cascade deformation between 44°N-45°N.
Further south (43°N-44°N), crosscutting faults of the Bald Mountain Caldera, Walker Rim, and Chemult Graben systems affirm a vigorous interplay between extensional fault scarps striking NW and NE. Furthermore, the dominant faulting at these latitudes is localized well to the east of the High Cascades, implying the major structure of the High Cascades is not a traditional graben. Assuming surficial fault scarp density is a proxy for where modern strain is localized, our new interpretations suggest that a wide zone of distributed faulting that extends well to the east of the High Cascades into the Central Oregon Basinand Range extensional province marks the eastern edge of the Oregon forearc block between 43°N-44°N.
Geologic Mapping in southern Oregon funded by USGS:
Title: Surficial Geologic Map of the West Klamath Lake Fault Zone, Klamath County, Oregon
Abstract: The Western Klamath Lake Fault Zone (WKLFZ) is located in the southern Oregon Cascade arc along the southwest side of Klamath Lake and the city of Klamath Falls. The terrain is dominated by volcanic ridges and by wide valleys filled with of basalt and basaltic andesite flows. Shield, sheet, cinder-cone, and Surtseyan volcanism are all present within the study area. The study area is dissected by meandering canyons of the westward flowing Upper Klamath River. Dozens of linear topographic escarpments crosscut the region and are interpreted as the surface expression of a complex system of oblique normal faults. These fault scarps strike NNW to NW and crosscut features of all ages, including two Holocene alluvial fans. This study combines field mapping and digital mapping. The base map used is a composite bare earth model (1-meter spatial resolution) generated from lidar data provided by DOGAMI to Oregon State University and stored on OSU’s lidar data server (ftp://lidar.engr.oregonstate.edu). Fault scarps are interpreted using the midpoint method.
Civil Engineering Research presented at the 2015 Bretz Club conference:
Title: Structure from Motion Digital Terrain Modeling
Abstract: Structure from Motion (SfM) digital terrain modeling utilizes the principles of parallax, stereo photogrammetry, and pattern recognition to calculate a three-dimensional point cloud from a series of overlapping but unstructured two-dimensional digital photographs. SfM is quickly gaining favor among the geological community because of its low cost and ease of use.
Geology Research in Alaska
I spent four years working as a subsurface geologist in Alaska. Unfortunately, intellectual property rules require all my work there to remain confidential.
Working on the shoreline of the Arctic Ocean in Alaska
Exploring Denali National Park
Gas processing facility in Prudhoe Bay
Taking a break at the beach
This is one of the drill rigs I worked on as a geologist.
Alaskan tundra in winter
Geology Research at the University of Wyoming (2007-2010)
Title: Patterns and timing of exhumation and deformation in the Eastern Cordillera of NW Argentina revealed by (U‐Th)/He thermochronology
Abstract: The Eastern Cordillera (EC) and related ranges of Bolivia and Argentina exhibit a wide variety of structural features, both thick and thin skinned, that make this region a prime area to study the evolution of these two contrasting styles. Using a combination of structural, geochronological, and thermochronological techniques, this study investigates how and in what order the various structures of the Argentinean EC from 25 to 26°S have developed during the Cenozoic. New mapping in the Angastaco area preserves one of the thickest Cenozoic stratigraphic sections and records a complex structural evolution during the Neogene, characterized by inversion of Cretaceous Salta Rift structures. Detrital zircon U‐Pb geochronology combined with stratigraphic and structural features typical of synsedimentary deformation constrains the age of orgenic growth in the area to ∼14 Ma. Detrital apatite (U‐Th)/He thermochronology on samples collected across the width of the southernmost EC at this latitude document an eastward younging of ages interpreted as the result of sequential eastward propagation of exhumation (and inferred deformation) from ∼14 to 3 Ma at a rate of ∼8.3 mm/a. Our data, when compared with existing data, show that the Puna Plateau of NW Argentina was exhuming and deforming at the same time as the EC and inter‐Andean regions of Bolivia, suggesting that the deformation front connects along strike despite of the differences in structural style. Whereas the deformation front reached the sub‐Andes of Bolivia by ∼10 Ma, deformation localized in the EC of NW Argentina until ∼4 Ma. Rates of propagation through the whole region seem to be quasi‐uniform regardless of different structural styles.
I presented these slides at my geology M.S. defense in 2010:
This is my thesis for my M.S. in Geology at the University of Wyoming:
Geology Research on St. Catherine's Island (2007)
Title: Two Decades of Shoreline Retreat on the North and East Sides of St. Catherine's Island, GA
POTTER, Donald B. Jr, PADGETT, B. Luke, and TRIMBLE, John D. Forestry and Geology, University of the South, Sewanee, TN
Abstract: St. Catherine's Island, GA, is a Holocene-Pleistocene barrier island with no artificial structures on the beach. Erosion of the east and north shores, augmented by accelerated sea level rise, was documented in the 1970s by McLain. The work has been expanded during the past 20 years to include more than 25 stations. At Engineer's Road on the north shore, a 0.8 m/yr southward migration of the beach into a forested Holocene dune field has left dead standing pines below the high tide mark. Growth of a large sand bar at the northeastern tip of the island has coincided with up to 20 m of lateral accretion below a 5 m-high Pleistocene bluff on the northern stretch of the east shore. In contrast, the southern 0.7 km-long stretch of this Pleistocene bluff has eroded at rates ranging from 1.3m/yr to 2.4 m/yr.
South Beach extends 4.8 km southward from McQueen's Inlet and has the highest rates of erosional retreat. Flag Pond was breached by 10.4 m of lateral erosion during a 1992 winter storm, and its freshwater flora has been replaced by saltwater species. Retreat of 2.1 m/yr at Beach Pond over the past six years has made the breach of this last fresh water pond along the eastern shore imminent. Washover of beach sand into marshes is common along much of South Beach, Middle Beach, and North Beach, resulting in exposure of marsh muds on the beach face as erosion progresses inland.
Education Research at Oregon State University
Title: Affect and Self-Efficacy in the Science Classroom
Abstract: This action research project studies the effect of an Ambitious Science Teaching (AST) unit on the affective domain and self-efficacy beliefs of students in two high school physics classes. Students were polled on their emotions and motivations at the end of six lessons that included model-based inquiry, video, discourse, laboratory inquiry, mathematical problem solving, a quiz, computer simulations, and outdoor data collection. Student responses were analyzed to determine the influence of each class on their affective domain and self-efficacy. Results suggest that model building and outdoor data collection were the most joyful and unstressed experiences, while the quiz and lab were the most stressful or tense experiences. Self- efficacy was highest at the end of days which involved modeling or empirical data collection and was lowest on days which involved the heavy use of mathematics or assessment. Students report the highest self-efficacy on days when they put in more effort than normal and perceived the difficulty to be low. These findings suggest that lessons involving student data collection through inquiry provide the most positive influences on self-efficacy and affect, while mathematical data analysis and formal assessments provide the most negative influences on affect and self-efficacy. Within the Ambitious Science Teaching framework, core practices one and two had relatively positive effects on affect and self-efficacy; core practice three was universally negative; and core practice four had mixed results depending on environment. I will use these results to incorporate more opportunities for student data collection through inquiry, and I will explore means of reducing stress and being more conscious of student affect during data analysis and formal assessments that ask students to challenge their existing ways of thinking.