Landscapes are shaped by sediment-transport systems with climate, tectonics and sea level as their ultimate boundary conditions. Variability is a hallmark of both the internal dynamics of sediment-transport systems (result from nonlinear feedbacks between fluid flow and sediment motion), and the external forces that shape the landscapes. Despite the pervasiveness of variability in geomorphologic and sedimentologic systems at a multitude of spatiotemporal scales, our current understanding of how landscapes respond to inherent variability present in external forces that shape the landscapes (e.g., climate, tectonics) is limited. Moreover, there is a dearth of quantitative metrics to address the preservation of intrinsically generated variability of sediment-transport systems a?? which may alter or mask records of paleo-environmental conditions a?? in the sedimentary record.
My current and future research lie under the broad theme of characterising variability in surficial processes and quantifying their depositional signature in the rock record. Current projects cover a broad range of space and time scales, from understanding the stochastic dynamics of bedform evolution and their record in cross-stratal geometries, to unravelling the effect of historical flood variability on river avulsions and delta evolution, to assessing the effect of climate-variability on the temporal trends in estimated erosion rates in mountain ranges.
Below is a summary of some current work that I'm pursuing.
River avulsions on deltas and their deposits
River deltas are highly dynamic, often fan-shaped depositional systems that form when rivers drain into a standing body of water. They host over a half billion people and are currently under threat of drowning and destruction by relative sea-level rise, subsidence, and anthropogenic interference. Deltas often develop planform fan shapes through avulsions, whereby major river channel shifts occur via "channel jumping" about a spatial node, thus determining their fundamental length scale. Emerging theories suggest that the size of delta lobes is set by backwater hydrodynamics; however, these ideas are difficult to test on natural deltas, which evolve on centennial to millennial timescales.
By appropriately scaling the dynamic backwater effects in physical experiments, we were able to build an experimental delta that grew through successive deposition of lobes, which maintain a constant size. Moreover, river floods cause erosion in the lowermost reaches of the alluvial river near their coastline, which may leave erosional boundaries in the sedimentary record that may appear similar to those previously interpreted to be a result of relative sea-level fall. My current research focuses on developing a better mechanistic understanding of river avulsions on deltas and mapping these mechanics into the rock record.
Quantifying paleo-landscape dynamics from the rock record
Sedimentary rocks are the archives of environmental conditions and ancient planetary surface processes that led to the formation of stratified rock. The geometry of sedimentary strata, thus, provide records of the sedimentary environments that once existed on Earth and Mars, for example. Accurate reconstructions of the past surface processes and the environmental changes that drive them remain limited, however, because we lack mathematical models to map modern geomorphic processes to the geometry of rock bodies that they form over geologic timescales. Consequently, reading the sedimentary record remains imprecise and controversial.
My current research focuses on gaining physical and statistical understanding of the surface processes of depositional systems and quantitatively linking them to the geometry of the associated sedimentary rock bodies. Using theory, experimental, and field investigations, we aim to develop quantitative methods to invert the geometry of sedimentary strata to derive both the morphology and the dynamics of the past planetary surfaces. Our preliminary research indicates that the shape of the rock bodies record the competition between translation and deformation (change in shape) of landforms as they evolve a?? parameters of surface evolution that are, in part, controlled by climate and tectonics. The primary aim of the proposed research is: (1) to build on these results by deriving general relations among morphology, dynamics of surface evolution, and stratal geometry and (2) to understand the environmental controls on the surface evolution of depositional systems.
Current and past collaborators
Mike Lamb, Woody Fischer, Jean-Philippe Avoauc (Caltech)
Sanjeev Gupta (Imperial College)
Efi Foufoula-Georgiou, Chris Paola, Vaughan Voller (SAFL, U. of Minnesota)
Kyle Straub (Tulane U.)
Brandon McElroy (U. of Wyoming)
Dirk Scherler (GFZ Potsdam)
Christoph von Hagke (U. of Aachen)
Gary Parker (U. of Illinois)
Bill Dietrich (U. of California, Berkeley)
Paola Passalacqua (U. of Texas at Austin)
Matt Golombek (JPL, NASA)
Colin Stark (LDEO, Columbia U.)
Jeff Nittrouer (Rice U.)