Geomorphic-Geodynamic Coupling at the Orogen Scale

One of the most provocative - yet largely untested - recent hypotheses concerning orogenic evolution is that regional variations in climate strongly influence spatial variations in the style and magnitude of deformation across an actively deforming orogen. Recent progress in quantifying rates of both tectonic and geomorphic processes and in modeling surface and lithospheric processes sets the stage for an integrated, quantitative, field- and model-based investigation of the interactions and feedbacks between geomorphic, climatic, and tectonic processes. We are examining these interactions in an orogen Not only is this the quintessential collisional orogenic belt, but its topographic growth and erosional history have been suggested as key controls on global climatic changes. Our integrated study focuses on a major transverse catchment, stretching from the edge of the Tibetan Plateau to the foreland and traversing some of the highest topography in the world. This transect spans the major structural elements of the Himalaya, as well as monsoon-to-rainshadow climatic conditions. We bring together expertise in process-based geomorphology, glaciology, climatology, structural geology, thermochronology, cosmogenic radionuclide dating, modeling, and documentary film making for a multi-pronged approach intended to evaluate one overarching, but largely untested hypothesis:

  • Rates of erosion vary spatially as a function of climate and this spatial variability in erosion controls the partitioning of deformation within an orogen.

Furthermore, we are collecting data to assess the following related, but subsidiary hypotheses:

  • The erosional response to rapid lateral advection of crust across a basement ramp crustal scale fault-bend folding, for examp, creates erosion rates that are nearly equal across the entire topographic escarpment of the Himalaya, ranging from 8 km to 1 km in elevation.
  • Above a certain threshold erosion rate, the topography attains a dynamic "equilibrium" or steady state that is independent of erosion rate.
  • Topographic characteristics (relief, slope angles, normalized river gradients) correlate more strongly with erosion rates than they do with variations in climate or lithology.

Despite the broad scope of these hypotheses and the impossibility of resolving all details, we have developed a research strategy that, over a four-year span, is enabling us i) to define the primary characteristics of denudation, rock uplift, climate, and topography across this Himalayan transect and ii) to calibrate some process-based "rules" for major erosional agents, such as glaciers, rivers, and landslides. A key to success is the integration of data from diverse subdisciplines (climate, geomorphology, tectonics) at the scale both of intensively monitored subcatchments and of the entire trans-Himalayan catchment. Spanning seven subdisciplines in earth and atmospheric sciences, this project brings together researchers from nine US institutions, one French research institute, and three governmental agencies in Nepal.