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.