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Harrison Gray, Ph.D

Earth's surface is shaped by the transfer of sediment across time and space. As we live on the Earth's surface, understanding this transport of sediment is key to the well-being of our species. I work on solving problems asscociated with landscapes and sediment transport using the tools of computer landscape evolution modeling and the trapped-charge phenomena known as luminescence.

Ph.D Geomorphology, University of Colorado - Boulder, 2018

M.S. Geology, Univeristy of Cincinnati, 2013

B.S. Earth Sciences, University of California - Santa Cruz, 2010

 

 

Science and Products

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scientists near Saratoga Springs, Death Valley

Quaternary Hydroclimate Records of Spring Ecosystems

Desert springs and wetlands are among the most biologically productive, diverse, and fragile ecosystems on Earth. They are home to thousands of rare, endemic, and endangered plants and animals and reflect the availability and health of emergent groundwater. Despite the ecological importance of these wetlands, our knowledge of how they might respond to predicted future climate change is limited...
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Climate Research and Development Program
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Quaternary Hydroclimate Records of Spring Ecosystems

Desert springs and wetlands are among the most biologically productive, diverse, and fragile ecosystems on Earth. They are home to thousands of rare, endemic, and endangered plants and animals and reflect the availability and health of emergent groundwater. Despite the ecological importance of these wetlands, our knowledge of how they might respond to predicted future climate change is limited...
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Shaded relief map of the Mojave Desert region, southern California, showing faults of the Eastern California Shear Zone.

Western Basin & Range - Eastern California Shear Zone

The Eastern California Shear Zone (ECSZ) Mapping project, funded by the National Cooperative Geologic Mapping Program, combines surficial and bedrock geologic mapping, geophysical surveys, and high-resolution topographic data analysis with neotectonic, geomorphic, structural, volcanic, and geochronologic studies to better understand the tectonic framework and landscape evolution of the ECSZ in the...
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National Cooperative Geologic Mapping Program, Geology, Minerals, Energy, and Geophysics Science Center
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Western Basin & Range - Eastern California Shear Zone

The Eastern California Shear Zone (ECSZ) Mapping project, funded by the National Cooperative Geologic Mapping Program, combines surficial and bedrock geologic mapping, geophysical surveys, and high-resolution topographic data analysis with neotectonic, geomorphic, structural, volcanic, and geochronologic studies to better understand the tectonic framework and landscape evolution of the ECSZ in the...
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Locations at Which Paleoseismological Studies Have Been Completed Along Principal Faults in the San Francisco Bay Area

Earthquake Geology and Paleoseismology

USGS scientists study active fault zones by mapping faults, excavating trenches, studying landforms offset by earthquakes, and measuring past and current motion of active faults using alignment arrays, global positioning systems (GPS), and airborne, terrestrial and mobile laser scanning technology.By excavating trenches across active faults, USGS geologists and collaborators are unraveling the...
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Natural Hazards, Earthquake Hazards
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Earthquake Geology and Paleoseismology

USGS scientists study active fault zones by mapping faults, excavating trenches, studying landforms offset by earthquakes, and measuring past and current motion of active faults using alignment arrays, global positioning systems (GPS), and airborne, terrestrial and mobile laser scanning technology.By excavating trenches across active faults, USGS geologists and collaborators are unraveling the...
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Data release for luminescence: Edwards Air Force Base (CA) and CA Water Science Center report including luminescence data and ages

The following report summarizes the dating results from Aeolian deposits within and around Edwards Air Force Base in California. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and dating related calculations. We recommend that this repo
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Geosciences and Environmental Change Science Center

DATA RELEASE Part 2: Optical luminescence dating of Bradley Lake, Oregon, tsunami deposits, analytical data for: A maximum rupture model for the central and southern Cascadia subduction zone-reassessing ages for coastal evidence of megathrust earthquakes

The following report summarizes the dating results from Bradley Lake, Oregon. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and datingrelated calculations. We recommend that this report be included as the supplementary material for any
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Geosciences and Environmental Change Science Center

Luminescence, weather, and grain-size data from eastern Chuckwalla Valley, Riverside County, California

This data release contains luminescence, weather, and sediment grain-size data from eastern Chuckwalla Valley, Riverside County, California. This study investigates sedimentary and geomorphic processes in eastern Chuckwalla Valley, Riverside County, California, a region of arid, basin-and-range terrain where extensive solar-energy development is planned. The objectives were to (1) measure local we
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Coastal and Marine Hazards and Resources Program, Geosciences and Environmental Change Science Center, Pacific Coastal and Marine Science Center
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A maximum rupture model for the central and southern Cascadia subduction zone—reassessing ages for coastal evidence of megathrust earthquakes and tsunamis

A new history of great earthquakes (and their tsunamis) for the central and southern Cascadia subduction zone shows more frequent (17 in the past 6700 yr) megathrust ruptures than previous coastal chronologies. The history is based on along-strike correlations of Bayesian age models derived from evaluation of 554 radiocarbon ages that date earthquake evidence at 14 coastal sites. We reconstruct a
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Natural Hazards, Geologic Hazards Science Center

Landscape evolution in eastern Chuckwalla Valley, Riverside County, California

This study investigates sedimentary and geomorphic processes in eastern Chuckwalla Valley, Riverside County, California, a region of arid, basin-and-range terrain where extensive solar-energy development is planned. The objectives of this study were to (1) measure local weather parameters and use them to model aeolian sediment-transport potential; (2) identify surface sedimentary characteristics i
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Coastal and Marine Hazards and Resources Program, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center, Pacific Coastal and Marine Science Center

Depth-dependent soil mixing persists across climate zones

Soil mixing over long (>102 y) timescales enhances nutrient fluxes that support soil ecology, contributes to dispersion of sediment and contaminated material, and modulates fluxes of carbon through Earth’s largest terrestrial carbon reservoir. Despite its foundational importance, we lack robust understanding of the rates and patterns of soil mixing, largely due to a lack of long-timescale data. He
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Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center, Geology, Geophysics, and Geochemistry Science Center

Luminescence as a sediment tracer and provenance tool

Luminescence holds unique potential as a sediment tracer and provenance method. The tracer application of luminescence has key advantages including ease of measurement, relatively low cost, and applicability to geologically ubiquitous quartz and feldspar sand and silt. These advantages can help answer fundamental questions about geomorphology, sediment transport, sediment production, and the tecto
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Geosciences and Environmental Change Science Center

Paleoseismic results from the Alpine site, Wasatch fault zone: Timing and displacement data for six holocene earthquakes at the Salt Lake City–Provo segment boundary

To improve the characterization of Holocene earthquakes on the Wasatch fault zone (WFZ), we conducted light detection and ranging (lidar)‐based neotectonic mapping and excavated a paleoseismic trench across an 8‐m‐high fault scarp near Alpine, Utah, located ∼6.2–0.4  ka∼6.2–0.4  ka. Interseismic recurrence ranges from 0.2 to 1.8 ky (mean 1.2 ky). We estimate 6.5±0.7  m6.5±0.7  m of cumulative vert
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Energy Resources Program, Mineral Resources Program, National Laboratories Program, Science and Decisions Center, Geology, Minerals, Energy, and Geophysics Science Center

Examining the relationship between portable luminescence reader measurements and depositional ages of paleowetland sediments, Las Vegas Valley, Nevada

Portable luminescence readers are exciting new tools that have the potential to rapidly determine the age structure of late Quaternary stratigraphic columns. This is important because high-resolution age profiling can reveal details about the temporal dynamics of climate cause and ecosystem effect, often while researchers are still in the field. In this paper, we compare new portable luminescence
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Climate Research and Development Program, Geosciences and Environmental Change Science Center

Application of a luminescence‐based sediment transport model

Quantifying the transport history of sand is a challenging but important goal in geomorphology. In this paper, we take a simple idea that luminescence is bleached during transport and regenerates during storage, and use this as a basis to re‐envision luminescence as a sediment tracer. We apply a mathematical model describing luminescence through an idealized channel and reservoir system and then c
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Groundwater and Streamflow Information Program, Geosciences and Environmental Change Science Center

Dating of river terraces along Lefthand Creek, western High Plains, Colorado, reveals punctuated incision

The response of erosional landscapes to Quaternary climate oscillations is recorded in fluvial terraces whose quantitative interpretation requires numerical ages. We investigate gravel-capped strath terraces along the western edge of Colorado's High Plains to constrain the incision history of this shale-dominated landscape. We use ¹⁰Be and ²⁶Al cosmogenic radionuclides (CRNs), optically stimulated
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Groundwater and Streamflow Information Program, Geosciences and Environmental Change Science Center

On extracting sediment transport information from measurements of luminescence in river sediment

Accurately quantifying sediment transport rates in rivers remains an important goal for geomorphologists, hydraulic engineers, and environmental scientists. However, current techniques for measuring long-time scale (102–106 years) transport rates are laborious, and formulae to predict transport are notoriously inaccurate. Here we attempt to estimate sediment transport rates by using luminescence,
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Climate Research and Development Program, Groundwater and Streamflow Information Program, Land Change Science Program, Geosciences and Environmental Change Science Center

User guide for luminescence sampling in archaeological and geological contexts

Luminescence dating provides a direct age estimate of the time of last exposure of quartz or feldspar minerals to light or heat and has been successfully applied to deposits, rock surfaces, and fired materials in a number of archaeological and geological settings. Sampling strategies are diverse and can be customized depending on local circumstances, although all sediment samples need to include a
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Geosciences and Environmental Change Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center

Variables and potential models for the bleaching of luminescence signals in fluvial environments

Luminescence dating of fluvial sediments rests on the assumption that sufficient sunlight is available to remove a previously obtained signal in a process deemed bleaching. However, luminescence signals obtained from sediment in the active channels of rivers often contain residual signals. This paper explores and attempts to build theoretical models for the bleaching of luminescence signals in flu
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Geosciences and Environmental Change Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center

Guide to luminescence dating techniques and their application for paleoseismic research

Over the past 25 years, luminescence dating has become a key tool for dating sediments of interest in paleoseismic research. The data obtained from luminescence dating has been used to determine timing of fault displacement, calculate slip rates, and estimate earthquake recurrence intervals. The flexibility of luminescence is a key complement to other chronometers such as radiocarbon or cosmogenic
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Geosciences and Environmental Change Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center

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