Research

Current and recent projects

Soil production and weathering in New Zealand

Collaborators: Kevin Norton, Tony Dosseto, Georgina King, Dennis Dahms

Soil production should be limited by rates of chemical weathering and erosion. Recent work has proposed a “speed limit” for soil production in rapidly eroding mountains, where erosion removes material before it has much chance to weather (Dixon and von Blankenburg, 2012). Soil production rates on the west coast of New Zealand’s Southern Alps appear to exceed that speed limit by an order of magnitude (Larsen et al., 2014). These sites are uplifting rapidly, and experience one of the wettest climates on Earth.

These observations raise a host of interesting questions about how this landscape is evolving, and about the broader interactions between climate, tectonics, and Earth’s surface. What sets the “speed limit” for soil production in this landscape, if one exists at all? How do climate and tectonics affect chemical weathering and soil production? This  is the main topic of my post-doctoral work – stay tuned for more.

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Mt Cook/Aorangi

 

Spatial variations in sediment size inferred from detrital thermochronology

Collaborators: Cliff Riebe, Leonard Sklar, David Shuster

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Inyo Creek, eastern Sierra Nevada

Sediment produced on mountain slopes is an important part of many surface processes. It influences rates of bedrock river incision and impacts fluvial habitats. Sediment also reflects the processes that erode the landscape, from rockfall to soil creep. Understanding how sediment size varies across a landscape is important for a range of geomorphic, hydrologic, and ecologic problems (Sklar et al., 2016).

This work constrains spatial variability in the sizes of sediment produced on hillslopes. I used detrital thermochronometry in sediment of many different sizes to trace each sediment clast back to its origins on the landscape. This allowed me to quantify how sediment size distributions change across a steep mountain landscape. This variability in sediment size likely reflect both topography and climate (Riebe et al., 2015; Lukens et al., in prep).

Grain-size bias in detrital studies

Collaborators: Cliff Riebe, Leonard Sklar, David Shuster

Spatial variability in the sizes of sediment produced on hillslopes may have implications for detrital studies of many kinds. These studies rely on the assumption that the material sampled from streams represents the material being eroded from the entire landscape. If we sample a narrow range of sizes in catchments where sediment size varies, we may inadvertently introduce bias.

Using numerical modeling, explored a range of conditions in which grain-size bias might arise in both cosmogenic nuclide studies (Lukens et al., 2016; JGR) and thermochronometry (Lukens et al., in revision).

Exhumation and tectonic history of the Pamir mountains, Tajikistan

Collaborators: Barbara Carrapa, George Gehrels, Brad Singer

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Murghab River, Gordo-Badakshan, Tajikistan

This work included Ar/Ar thermochronometry and U-Pb geochronology in river sediment to constrain the exhumation history of the Pamir mountains, which lie northwest of the Himalaya. Major tectonic terranes in the Pamir also correlate to terranes in Tibet, which provides some insight into the tectonic history of the region (Lukens et al., 2012; Tectonics).

 

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