This dissertation focuses on the dynamic relationship between evolving tectonics andsurface processes within the northwest Himalayas. By understanding how erosion at
the surface has varied over space and time during the past several million years, the
underlying mechanisms controlling how rock and sediment is redistributed can be identified.
The studies described in Chapters 2-4 predominantly use two methods to estimate
erosion rates: measurements of cosmogenic 10Be from stream sediment, which captures
erosion rates over millennial timescales, and low-temperature thermochronometry, which
can record erosion over timescales of millions of years. These datasets integrate erosion
rates over different timescales and, when used in conjunction with each other, produce
an improved understanding of the erosional history of a given landscape. In Chapters
2 and 3, we apply these methods within the Sutlej River drainage to better understand
the history of large-scale drainage capture and identify mechanisms that may have
facilitated drainage reorganization. Chapter 2 uses knickpoint celerity modeling, paleotopographic
reconstructions, 10Be-derived denudation rates, and topographic analyses
of drainage divides to quantify the magnitudes and timescales of erosion driven by capture
of the Zhada Basin, an ∼23,000 km2 extensional basin in southern Tibet. This
work finds that capture occurred at 735±269 ka and that capture-driven incision has removed
2010±400 km3 of sediment from the Zhada Basin since then. These findings also
help identify several plausible tectonic or autogenic driving mechanisms for the capture event, which are investigated further in Chapter 3. Chapter 3 uses a new dataset of
(U-Th)/He dates collected from the Sutlej River valley, along with a suite of numerical
incision models, to assess whether Quaternary displacement occurred along the South
Tibetan Detachment System (STDS) and how it could be mechanically connected to
large-scale drainage capture throughout the Himalayas. Incision models that incorporate
normal-sense slip consistent with active faulting along the STDS best correspond with
the pattern of exhumation inferred from (U-Th)/He dates, suggesting that headward
erosion and base level fall driven by displacement along the STDS could be a regional
driver of drainage capture. Chapter 4 uses estimated denudation and exhumation rates
over millennial- and million year-timescales, respectively, to interpret regional uplift patterns
in the northwestern Himalaya. 10Be-derived denudation rates, inferred exhumation
rates from published thermochronometric datasets, and estimated denudation mapping
using ksnQ, an enhanced form of the channel steepness index, reveal the recent behavior
of Lesser Himalayan duplexing, which largely influences surface topography and seismic
activity. Duplexing has not migrated since at least ∼4Ma, suggesting that the Himalyan
orogenic wedge may be segmented, such that cyclical development of a midcrustal ramp,
and associated duplexing, may occur asynchronously along the orogen. This may explain
observed patterns in exposed geology, topography, and exhumation rates in the northwest
Himalayas.