43994-AC8
Morphological Modeling of Continental Slopes
There have been delays in assigning a researcher to this project and we are only now expecting expenditure to begin in October. This was mainly caused by the PI's move to Manchester. Given the broad scope of this project, we considered a postdoctoral researcher important for progress and persuaded the University as part of Mitchell's relocation package to extend the researcher's tenure from the 14 months possible with the ACS funds to 22 months. Following a second round of advertisement and interviews, we are delighted to say that Dina Vachtman has accepted the position. We now look forward to great progress with the funds the ACS has kindly provided.
Appointed Researcher
Dina Vachtman is joining us with a remarkable combination of expertise in fluid dynamics, field experience and interests in Marine Geology which should provide an excellent background for the project. She has just finished her PhD at the Ben Gurion University of the Negev working with Jonathan Laronne, on streams initiated around the Dead Sea where declining water level has exposed springs. Those flows have been measured using ultrasonic Doppler velocimeters and other instruments in a way that demonstrates an impressive ability to make detailed field measurements and technical knowledge. Her fluid dynamical characterisation of flow structure has focused on secondary circulations and their relationships to the channel micro-relief. Those circulations in turn affect erosion of the (cohesive) bed, which she has characterised using geotechnical tests. Although some channels are initially straight, they develop remarkably complex bed morphologies from erosion and associated complex secondary circulations.
Prior to her PhD, Dina was introduced as an undergraduate to Marine Geoscience by Yossi Mart and later Dina carried out a project with Yossi on submarine channels offshore Israel to study whether they were created in the submarine environment or subaerially during the Miocene drawdown of the Mediterranean. During her PhD, she joined a marine expedition to the Black Sea with Bill Ryan of Lamont. She is thus unusually experienced and has a strong interest in Marine Geoscience besides her geomorphology.
Research Plans
Given Dina's maturity and in the interests of her development, we wish her to lead the planning of her work, of course with advice from the PIs. The following ideas are only provisional thoughts.
Given Dina's experience of secondary flow dynamics, we are exploring whether the pattern of secondary flows in turbidity currents could be inferred from the patterns of dunes revealed in deep-towed sidescan sonar images of canyon floors. As dunes are shaped by bedload of sand and gravel, the orientations of their crestlines reveal the patterns of near-bed flow. This could provide an opportunity to work out how flow dynamics are affected by topography, in turn affecting the transport of bed material, erosion and morphology.
Our original studies of canyon longitudinal profiles considered relatively few canyons in restricted environments. A possibility will be to characterise many canyon longitudinal profiles from a range of environments to see if the effect of differing sediment input etc on morphology can be inferred.
We had mentioned using basins of the California Borderlands to study how canyon incision is related to the amount of sediment that has passed through them. An MSc student looked into this last year. Santa Monica Basin appeared the most suitable as there is much seismic data as well as ODP sites. Unfortunately, it has proven more difficult than anticipated to characterise fully the sediment that has passed down individual channels because of the way fans overlap. Furthermore, the stratigraphy towards the base of fans is obscure in the seismic data. There is a superficial relationship between sediment through-put and erosion as the deepest and widest canyons are associated with the largest topography of fan beneath them, but we have been unable to quantify the observations adequately and are searching instead for more suitable sites.
Concerning the diffusion analysis, given its restricted application to certain sandy environments and currents, we are now more cautious. A sand deposit mapped north of La Jolla, California has a simple clinoform rollover morphology. It should form a good target for such a study as the clinoform formed during the Holocene period when oceanographic conditions were likely similar to those of the present day. Researchers at SIO have collected oceanographic and geophysical data (ADCP, waves, Chirp, multibeam and vibrocore) and we are exploring with them scope for modelling.
Dina has co-proposed a special session on Submarine Geomorphology for the 2009 European Geoscience Union meeting. It intends to bring together subaerial geomorphologists and marine geoscientists to help bridge the discipline divide and it should provide an excellent platform for Dina to publicise the ACS research.
We thank the ACS for generously providing this grant and despite the long delays in starting we anticipate some exciting work over the coming years.
