Past and Present Research Projects

Effect of backwater dynamics on sediment transport from river sources to marine sinks

Near river mouths, sediment transport is affected by decelerating flow, or backwater, that results from the river's interaction with the stagnant water beyond the shoreline.  We are using theoretical modeling, field data from the modern Mississppi River, and flume experiments to investigate morphodynamics of backwater zones.  Preliminary work has shown that backwater can significantly affect the transfer of sediment from river sources to marine deposits.  Work in progress in collaboration with Jeff Nittrouer and David Mohrig, UT - Austin.

=

Mississippi River, USA.

Boulder transport in steep mountains streams and the development of step-pool bedforms.

Coarse sediment lines the beds of mountain streams.  Understanding the mobility of this sediment is important for a wide range of concerns including: landscape evolution, routing sediment from source to sink, fish habitat, and debris flow initiation.  We are using field measurements, cosmogenic dating, theoretical modeling and flume experiments to investigate sediment transport and stream-bed morphology of mountain streams.  Work in a recent publication of a theoretical model shows that sediment is inherently more stable in steep mountain streams compared to lowland rivers due to fundamental changes in flow hydraulics.  Work in progress.

Step pools in Kauai

Climate change and the formation of fluvial strath terraces

We are using a combination of numerical modeling, remote sensing, and field work to better understand river terrace formation and how it relates to climate change. Work in progress by Ajay Limaye.

Terraces near the Henry Mountains, UT

Mechanics of waterfall erosion

Waterfall erosion into bedrock is one of the fundamental drivers of landscape change in hilly and mountain regions.  We investigated waterfall erosion in fractured rock using a set of flume experiments.  The results indicate the rock fracturing exerts a dominant control of waterfall process and form (see Publications and Movies).  Ongoing work includes  a series of field and flume experiments designed to develop a process based model for the retreat of waterfalls by plunge pool erosion. This includes rappelling into active plunge pools (top).

Joel Scheingross in Little Santa Anita Canyon, CA

Photograph of experimental waterfall

Catastrophic erosion of Canyon Lake Gorge, TX, by plucking

In 2002, catastrophic release of water from Canyon Lake, Texas, transported meter-sized boulders, excavated ~7 m of rock, and transformed a soil-mantled valley into a bedrock canyon in ~ 3 days.  We find that canyon morphology is strongly dependent on rock type where plucking of limestone blocks produced knickpoints, inner channels, and strath terraces, and abrasion of cemented alluvium sculpted walls, plunge pools, and streamlined islands (see  Publications). 

Photograph taken during the 2002 event by Richard Sears.

Plunging hyperpycnal river plumes and their deposits

Hyperpycnal flows are turbid river plumes that can plunge to form turbidity currents where they enter a water body of lesser density.  Because these flows provide one of the most direct connections between terrestrial sediment sources and marine depositional sinks, their deposits might preserve an important record across a variety of climatic and tectonic settings.  We used a series of flume experiments and a numerical model to investigate the connection between river flood dynamics and hyperpycnal flow deposits (see Publications and Movies).  In some cases, hyperpycnal flow velocities can be anti-correlated to river discharge doe to movement of the plunge point.

Photograph of an experimental plunging river plume

Amphitheater-headed canyons on Earth and Mars

Fluvial erosion into bedrock is one of the fundamental drivers of landscape evolution. The morphologies of bedrock canyons (e.g., amphitheater heads shown to the right) contain clues about the history of formation with important implications for astrobiology on Mars. We have been working to understand the mechanics of bedrock-erosion processes and the connections between process and form, using observations of canyons on Mars and Earth (Hawaii, Idaho, Colorado Plateau), theoretical modeling, and physical modeling.  This work has led to  publications on a model for abrasion by suspended sediment, an analysis of the seepage-erosion hypothesis, a model for valley formation by plunge-pool erosion in Hawaii, and the discovery of a catastrophic outburst flood in Idaho. 

Nirgal Valles: NASA/JPL/MSSS

Wave influenced hyperpycnal turbidity currents and their deposits.

With Paul Myrow, we have discovered evidence of wave-influenced turbidity currents in the rock record.  The photo of the Minturn Formation, Colorado, shows evidence for deposition first during an accelerating flow and later during a deceleration flow.  This is consistent with deposition from a hyperpycnal turbidity current that was directly fed from a flooding river.  Other beds in the same outcrop show evidence for storm-wave activity. See two  publications in the Journal of Sedimentary Research form more information.

Hyperpycnite: Minturn Formation, Colorado

Evidence for turbidity currents in Eel Canyon, CA

Through analysis of a new bathymetric map of the submarine Eel Canyon, offshore California, we have discovered morphologic evidence for recent turbidity-current activity.  In a GSA Bulletin publication, we propose that turbidity currents superelevate at the dramatic 90 degree bend in the canyon, and they are responsible for incision of a distributary channel, cyclic step bedforms, and a northerly displaced fan lobe.

Bathymetric map of Eel Canyon, California

Rainfall and sediment transport on Titan

Branching valley networks near the landing site of the Huygens probe on Titan (Saturn’s largest moon) imply that flowing fluid has eroded the surface. The fluid was most likely methane, and the eroded material was probably composed mostly of water ice.  We show that the properties of these materials at Titan’s surface and the morphology of the networks suggest that the valleys were eroded mechanically by surface runoff, and use the valley network morphology to estimate the methane precipitation rates required to form these features (publication).

Branching networks on Titan

NASA/JPL/ESA/U. Arizona

Wave generated suspensions

The transport of sediment across modern continental shelves is likely dominated by the movement of dense fine grained suspensions (high-density suspensions or fluid mud) that form at times of high wave energy during storms. We produced high density suspensions in an oscillatory duct and found that the suspensions significantly reduced the size of the wave boundary layer from about 3 cm to less than 3 mm.  Despite this, the high-density suspensions were 3-8 cm thick and were supported by turbulence that was transported into the upper water column from a region very near the bed where the it was produced (publications). See movies of these experiments.   

High-density suspension in a oscillatory duct

Turbidity currents in intraslope minibasins

Many minibasins that found on continental slopes such as in the Gulf of Mexico have been gradually filled by turbidity currents.  We tested different models of minibasin filling including continuous turbidity currents and pulse-like flows in an experimental basin.  As reported in a series of publications, we found that continuous and surging turbidity currents created unique turbidites, in which the deposits from surging turbidity currents were notably more ponded.  In addition, we found that even large sustained flows may not fill more than one basin at a time due to the interaction with minibasin topography which caused formation of a hydraulic jump, development of a settling interface, and detrainment of water across that interface. See movies of these experiments.   

Turbidity currents in a flume