Because of its low relief, mid-continent location, and preserved alluvial sedimentary archive, the Buffalo River presents an opportunity to extend the range of landscape evolution studies to an under-represented end-member in the range of landscapes. This project will: i) create a quantitative reconstruction of the incision history of the Buffalo National River from the record of sediments stored in alluvial drapes on strath terraces and in subterranean caves ii) develop and interpret the sedimentary record of changes in fluvial processes operating in the Buffalo River catchment during the Quaternary Period and iii) define the ways that streams in catchments with heterogeneous lithologies in low-topography, mid-continent catchments, such as that of the Buffalo River, respond to base level fall. The features of interest for luminescence dating are former channel fills and gravel bars now perched above the channel as terraces. These sediments are mixed gravel, sand, and fines overlying bedrock straths and as such, the dosimetry is complex. Because the samples are heterogeneous this research requires in-situ measurements of gamma dose for an accurate assessment of dose rate.
The research contributes to long-lived fundamental questions in geomorphology concerning the role of lithology in landscape evolution and the significance of unpaired stream terraces in interpretation of the geomorphic record. The outcomes of this research will contribute to understanding the ways that landscapes respond to base level fall that are central to interpreting spatial and temporal variation in sediment storage and erosion and therefore have implications for several societal concerns (e.g. soil loss, pollutant sequestration in soils and floodplains, and flood attenuation). These results will also facilitate reconstructions of the evolution of the Earth's surface in the mid-continent of North America which can provide baseline information from pre-human landscapes to contextualize human impacts and thus guide restoration and management. For more info, see the Buffalo River Geoscience webpage.
Collaboration with Amanda Keen-Zebert (Desert Research Institute) and Stephen Tooth (Aberystwyth University). Mixed bedrock-alluvial anabranching rivers form some of the world’s most spectacular fluvial scenery but their dynamics remain poorly documented. Previous conceptual models have outlined how alluvial islands form on the underlying bedrock template but timescales of island development are largely unknown owing to limited geochronology. This study uses optically stimulated luminescence (OSL) dating to establish the growth rates and stability of alluvial islands on the Vaal River at Parys, South Africa. The Vaal traverses the World Heritage-listed Vredefort Dome, an eroded, ancient meteorite impact site. The river enters and exits the dome as a 150-170 m wide single channel flanked by sedimentary rocks, but changes to a distinctive 1.5 km wide anabranching river with 10-15 channels and numerous islands as it flows across granitoid rocks exposed in the dome's core. The numerous islands are formed of rock and/or alluvium, and support extensive native riparian tree communities, providing habitat diversity that contrasts with the surrounding semi-arid, grass- and shrub-covered terrain. We measured the age and aggradation rates of 9 islands in the anabranching reach using OSL. Single grain measurements of quartz were made using the single aliquot regenerative dose (SAR) approach. Equivalent dose populations have up to 60% overdispersion, common for fluvial samples, and the minimum age model was used to calculate final ages. Results demonstrate that the complex of alluvial islands is relatively young, with all having formed in the past 1000 years. The alluvial islands grow rapidly (mean vertical aggradation >0.28 cm/yr) during low to moderate floods (Q <2500 m3/s) owing to interactions between sediment deposition in the lee of bedrock outcrop, tree colonisation, and island coalescence. Islands tend to erode during larger floods through lateral erosion, vertical stripping, and dissection by newly-forming anabranches. The ages demonstrate that the alluvial islands are essentially dynamic, short-lived features that develop on a bedrock template that is underlying slower, long-term erosion. Our goal is to expand this dataset to include bedrock cored islands and place the age of formation of the islands in the context of the age of the broader floodplain within which the island complex exists. These findings will contribute to geoheritage education and to ongoing development of sustainable management plans for the tree-covered islands, many of which are threatened by altered flow regimes, invasive species, and encroaching tourism developments.
Collaboration with David Furbish, Dan Morgan, and Joshua Roering, Tyler Doane, and Amanda Keen-Zebert. Recent work on the sediment transport on hillslopes suggests a need to clarify the implications of ‘nonlocal’ versus ‘local’ transport processes and associated formulations of the sediment flux, as expected hillslope behavior under these two conditions is quite different. However, the supporting theory has outpaced experimental and field-based observations needed to inform the theory. This project is aimed at closing this gap, as implications for understanding hillslope evolution are far-reaching. The project will: (1) combine experiments with scaling analyses to clarify ingredients of rarefied particle-surface interactions during their downslope motions, as these influence key processes of sediment disentrainment; (2) explore theoretical formulations of nonlocal transport for two-dimensional topography that is convergent-divergent in planform; (3) combine field observations with modeling work centered on hillslopes in the Oregon Coast Range and moraines in the Sierra Nevada Mountains, specifically selected to reveal ingredients of nonlocal transport behavior; and (4) formulate descriptions of nonlocal transport with appropriate space-time averaging in order to take into account the discontinuous (patchy, intermittent) nature of sediment motions on steepland hillslopes, as is necessary for treating the sediment flux as a ‘smooth’ (time differentiable) quantity.
In collaboration with the staff of the DRILL, Amanda Keen-Zebert is conducting research focused on the intersection OSL dating techniques, sediment transport, and hydrology. The research design includes field, physical lab experiments, and OSL techniques and addresses multiple objectives: 1. Defining a OSL bleaching statistic that relates the magnitude of partial bleaching of the luminescence signal in fluvial sediment systematically to the depositional context (flow rate; distance travelled in a watershed, stream, or bar) such that OSL bleaching statistics can be used as a paleoenvironmental proxy. 2. Differentiate the luminescence signal resetting characteristics of human-disturbed surfaces naturally reset sediments. 3. Elucidate the relationship between luminescence signal resetting, sensitivity, and sediment transport distance. A pilot study for this project was funded by a Short Term Innovative Research (STIR) Grant from the Army Research Office (ARO) and by internal funding from DRI that supported field work before and after a controlled dam release on the lower Colorado River.
Collaboration with Amanda Keen-Zebert, Ken Adams (DRI) and Kathleen Rodrigues (AKZ’s PhD advisee at UNR/DRI). This work has 2 goals: to develop a thermoluminescence method to directly date eruption timing from volcanic glass, and to define the degree of re-working of tephras using luminescence resetting statistics (rather than age dating). We have conducted preliminary field work to collect tephra samples of known age from the Great Basin. Kathleen has successfully dated some of the tephras with thermoluminescence and has preliminary results that align with the correct age. She is working to reduce the error to refine the dating approach. (Photos from Ken Adams.)
Collaboration between Amanda Keen-Zebert and Kathleen Nicoll, University of Utah. The goals of this research are to improve the understanding of bay mouth bar formation and to better develop the chronostratigraphy of the Bonneville Basin in order to reconstruct landform evolution and lake history as a function of hydroclimatic change. The research strategy combines geochronology (OSL, diagnostic artifacts) and Ground Penetrating Radar (GPR), field mapping, and sediment characterization to develop the chronostratigraphy of the Stockton Bar. We have conducted field work, analyzed a suite of preliminary OSL samples and diagnostic artifacts, and published those results in Journal of Archaeological Sciences.
Collaboration with Bradley Johnson (Davidson College) and Amanda Keen-Zebert (DRI). Lake Michigan shoreline dunes are unique features of the landscape both geomorphologically and in terms of ecosystems. Despite a number of recent studies examining the geomorphic history of Lake Michigan dune complexes, there is disagreement about the timing and controls on dune activation, migration, and stabilization and the relationship between lake level and dune activity. In particular, it is uncertain if dune behavior is exclusively related to dune type and morphology or if there is a more gradational change in behavior associated with latitudinal climate variation.
Several characteristics of the Green Point Dune Complex (GPDC) on the northeast coast of Lake Michigan make it an ideal site to investigate the controls on dune activation and stability in order to resolve the contradictions of previous studies. The accuracy of OSL dating in the region has been verified by previous studies that used radiocarbon ages as an independent control on OSL results. In this study, mapping, soils chronostratigraphy, and absolute age dating through OSL will be used to test the hypothesis that lake-plain dunes along the northeastern coast of Lake Michigan at the Green Point Dune Complex evolved similarly to lake-plain dunes to the south and that latitudinal climate variation played little role in the evolution of lake-plain dunes. The chronostratigraphy derived from the OSL results will be used to determine periods of dune activity and the timing of stabilization. Results will contribute to a more complete understanding of the timing and cause of dune activity along the eastern coast of Lake Michigan which will contribute to informing strategies for modern dune management.
Collaboration with Ben Odhiambo Kisila (University Mary Washington). This project has arisen out of the observation of hillslope erosion rates that are disconnected from channel incision rates in the entrenched meandering rivers like the Buffalo River. We will use a multi-geochronological approach to define the timescales of hillslope response to channel incision using OSL, 210Pb erosion rates, and 137Cs sediment fingerprinting.
Collaboration with Russ Adams (University of Waterloo), Hannah Friedman (Texas Tech University), Amanda Keen-Zebert (Desert Research Institute). The primary objective of this multi-disciplinary research project is to quantify the environmental legacy and biological consequences of industrialization, issues that both scientists and policy makers continue to grapple with in modern society. Two of key questions raised are: 1. What is the long-term environmental footprint of large scale mining and extractive metallurgy on the surrounding landscape and environment? and 2. What are the enduring consequences of these activities on humans? Research into the effects of mining and smelting is usually conducted at sites with less than a hundred years of this type of activity; within the Faynan Basin of southern Jordan we have the opportunity to investigate a landscape that has been impacted by nearly 5000 years of copper mining and smelting. This creates a unique natural laboratory for the study of how anthropogenic pollution moves across an active and complex landscape over time. Preliminary research has allowed us to develop a methodology for analysis of pollution with the examination of a small cluster of sites and the spread of residual pollution in the landscape surrounding them. This work will scale up this research to investigate the movement of pollution on a basin-scale level of analysis. This work builds on 25 years of archaeological investigation of early metallurgical research in the Faynan Basin by developing a comprehensive overview of the emergence of early copper industrialization and its impact on ancient populations and the environment.
Collaboration with Loren Davis (Oregon State University) and Amanda Keen-Zebert (DRI). Funded by the Lander Foundation. The Cooper’s Ferry Archaeology site, located on an alluvial terrace at the confluence of Rock Creek and the Salmon River in Idaho, is shedding new light on lithic technologies in the Western United States. At the site, the highest densities of artifacts are in pit features that appear to be dug into the lower stratigraphic units. Owing to a lack of suitable material for radiocarbon dating, we will use single grain optically stimulated luminescence (OSL) to define the chronology of older units into which the pits are dug to establish the maximum age of the occupation. In one of the pits at the site, variations in sediment color suggests multiple episodes of use. We expect that OSL dating of sediment within the pit will establish both the age of pit usage and that the feature post-dates the surrounding sediment, confirming that it is in fact a pit. We also expect that OSL equivalent dose (De) distributions in the sediments deposited naturally by the stream will be less scattered than the sediment within the pit, which we expect to have widely scattered equivalent dose distributions.