Professor Rolf Aalto
Associate Professor in Physical Geography

Research

Research interests

[For Publications please see Google Scholar Link below]

In 2007 I moved to the University of Exeter from the University of Washington (Department of Earth and Space Sciences, where I remain an Affiliate Associate Professor).  Research continues on many of my previous projects, with all my field samples, X-radiographs, and other data (thousands of cores and samples from five continents) safely in cold storage at Exeter. I have a diverse range of research projects underway, mainly overseas and primarily focused on the morphodynamics of rivers and erosion within the last 200 years. (However, I am increasingly investigating processes and fluxes over the Holocene and beyond.) My laboratory work in the Exeter Radiochemistry Lab features exceptional accuracy and capacity (40 alpha spectrometers & 15 gamma spectrometers with bespoke digital electronics and shielding for very low noise), support by expert technicians, and a matched capacity for the quantification of sample clay fraction (4 Sedigraphs, several laser grain sizers, and a Gemni series BET analyzer). Other research methods include applying novel sub-bottom CHIRP sonar equipment and long-baseline DGPS techniques for surveying various large rivers and lakes in the tropics, all synthesized and analyzed using ArcGIS and Fledermaus. I also collaborate extensively with biogeochemists to study the controls on carbon fluxes through tropical and temporate fluvial systems.  

I am currently involved with the supervision of three PhD students, who are all working on international projects. I also supervise undergraduate dissertations on various aspects of the above topics, and am proud that many of my past students have experienced successful employment in their area of study (both graduate and undergraduate). I welcome proposals from students (or any interested scientists) to carry out collaborative research in any of the research areas described.

With our high-precision alpha spectrometers we can measure surface-adsorbed 210-Pb to an exceptional degree of accuracy (1.5 - 3% one sigma error) as well as correct for subtle variations in the fraction of clay within sedimentary deposits. We are thereby able to characterize and date sediment accumulation (or scour) events from most places on Earth (often to within 1-2 years resolution). We can trace the origin of many types of particulate material and measure a wide range of physical, chemical, and biogeochemical characteristics within that material.  We also prepare samples for 10-Be and 14-C dating at Exeter, and collect and prepare samples for OSL dating at other institutions, most recently using 10-Be Meteoric to track erosion of topsoils following European Settlement in the USA. This suite of approaches allows us to quantify processes, track sediment, and close mass budgets needed for understanding the morphodynamics of hillslope and fluvial environments across many spatial and temporal scales:

  • Climate forcing of particulate fluxes and processes in fluvial dispersal systems (impact of ENSO and climate change).
  • Sediment exchange and carbon sequestration fluxes in river-floodplain systems (modern and historical mass balances and sediment-carbon biogeochemical associations in dynamic tropical river basins).
  • Controls on sediment and carbon fluxes from mountain ranges.
  • Refinement of techniques for high-resolution dating of the accretion and surface exposure ages of sedimentary deposits utilizing Clay-Normalized Adsorbed eXcesS 210Pb activity (CNAXS).  Dating of floodplains with the CIRCAUS technique (Constant Initial “Reach” Clay-normalized Adsorbed activity, Unknown Sedimentation rate), a refinement of the CICCS technique pioneered at Exeter. 
  • Sub-bottom imagining of sedimentary deposits and stratigraphy in rivers and lakes.
  • Analysis of river morphology using long-baseline DGPS and reprocessed SRTM elevations.
  • Modelling of fluvial processes using numerical models (eg., Delft3D, HEC-RAS) and scale models of lowland rivers.
  • The role of sedimentary basins in the global carbon cycle (variations in the processes and efficiency of organic carbon burial over the Neogene and the resulting impact on Earth’s organic subcycle).
  • Remote sensing of channel change in a wide range of fluvial environments, and GIS modeling of cumulative environmental impacts and watershed analysis (e.g., ArcGIS 10.1 modeling with ArcHydro, HEC-GeoHMS, HEC-GeoRAS, etc.)

I am always happy to give talks to scientific and general audiences about any of the above research.

 

Research projects

My research is well-supported by UK and international funders, with ~$10M in awards and an excellent proposal success rate. Through many productive research collaborations I have developed a strongly interdisciplinary view on science and research funding, having won multiple awards each from NERC, NASA, NATO, and especially NSF (where my funding success has crossed five NSF programs: Sedimentology, Integrated Carbon Cycle, Geography, Oceanography, and Critical Zone). I have similarly reviewed proposals and papers in all of these disciplines, placing me in an excellent position to advise and collaborate across the Earth Sciences.  

 

Basin Specific: Mekong River, Cambodia

  • Climatic and Autogenic Controls on the Morphodynamics of Mega-Rivers: Modelling Sediment Flux in the Alluvial Transfer Zone.
  • Floodplain sampling and surveying, laboratory work, GIS and SRTM analysis, biogeochemistry & some channel surveys.

The overarching goal of the project is to determine the factors that control the movement of sediment through the ‘transfer’ reaches of large rivers to their deltas and receiving basins downstream. NERC NE/J021571/1 project (£1.1M, 2012-2015) in collaboration with Andrew Nicholas (Exeter), Steve Darby (Southampton), and Dan Parsons (Hull).

Basin Specific:  Fly River, Papua New Guinea

  • Geomorphodynamic Modulation of Biogeochemical Fluxes and Basin Stratigraphy of the Fly and Strickland Rivers (Papua New Guinea).
  • Rates, timing, character, and processes for sediment/carbon delivery from the mountains and floodplains of Papua New Guinea.

Subject of six publications since 2005 and a recently funded NSF Margins Source-to-Sink Project ($613k, 2008-2013) written in collaboration with M.Goni, W.E. Dietrich, A.Aufdenkampe, and J.W. Lauer.  Major research focus, with involvement of Michael Grenfell (Gloucestershire). 

Basin Specific:  Cristina Basin Critical Zone Observatory (Pennsylvania, USA)

  • Spatial and temporal integration of carbon and mineral fluxes: a whole watershed approach to quantifying anthropogenic modification of critical zone carbon sequestration.
  • Weathering and Erosion Controls on Carbon-Mineral Complex Formation, with a specific focus on quantifying and tracing hillslope and fluvial processes that supply “fresh” minerals to soils.

NSF Critical Zone Observatory ($4.4M, 2009-2014) grant co-written in collaboration with A. Aufdenkampe, K. Yoo, J. Pizzuto, L. Kaplan, and D. Sparks. Major research focus, with involvement of PhD student Julia Marquard (funded by separate £58k grant) . 

Basin Specific:  Beni River, Bolivia

  • NERC Standard Grant "Do Floods Matter? Bridging the Gap between Morphodynamics and Alluvial Architecture." 
  • Quantifying and modelling the decadal to Holocene evolution and morphodynamic adjustment of a large, pristine tropical river to climate and tectonic forcing. 

NERC Standard grant (£710k, 2011-2014) co-written with A. Nicholas, L. Aragao, and G. Sambrook Smith. Major research focus, with involvement of PhD student Simon Buckley and postdoc Arved Schwendel. Subject of 6 major publications, with more manuscripts in preparation.

General Amazon (Rivers in Bolivia, Peru, and Brazil)

  • Sediment and biogeochemical fluxes in Bolivian and Peruvian rivers.
  • Geomorphic controls on Andean denudation rates.
  • Modelling and measuring floodplain sedimentation, flow dynamics, and climate response in Amazonian rivers.
  • Rates, timing, character, and processes for sediment/carbon delivery from the Andes of Bolivian and Peru.

Subject of 8 publications since 2002 (and numerous in prep), a NASA grant, and three funded NSF projects, including a top-rated Integrated Carbon Cycle Research project.  Key collaborators include A. Aufdenkampe, L. Maurice, T. Dunne, and D.R. Montgomery.  Continued research focus with projects in final stages of completion, subject of several undergraduate dissertations and a pending research project.

Basin Specific:  Sacramento River, California

  • Tracing and dating deposits of historical sediment (hydraulic mining debris from the California Gold Rush) in the Sacramento River.
  • Transport and deposition of sediment in bypass systems and remnant floodplains.  
  • Development of new dating techniques for dry, sandy floodplains.

Recent work with several papers published or in review, funded $275k project by NSF and CALFED.  Key collaborators are M. Singer and A. James.  Major research focus, with involvement of PhD student Mathias Will and undergraduate dissertations.

Basin Specific:  Danube River, Romania

  • Floodplain accretion and channel constriction in the Danube River.
  • Heavy metal concentrations in Danube River sediment.

Recent work along the lower Danube in collaboration with M. Singer and D. Balteanu, funded by NATO “Security through Science.”  Initial results (analysis of sediment cores and GIS study) promising, with papers and new proposals pending.  Subject of several undergraduate dissertations. 

Basin Specific:  Pilot Projects

  • Hillslope & fluvial response following large wildfires in mountainous catchments in Idaho (2009 NSF funded project with E. Yager).
  • Floodplain accretion along the Orinoco River (2009 EU funded project with J. Steiger).
  • Floodplain accretion in San Diego wetlands (2009 NSF funded project with T. Biggs).
  • Floodplain accretion along the Mekong River (NSF funded work with J.E. Richey).
  • Frost boil dynamics using 210Pb as a tracer for soil movement, Greenland (published research with B. Hagedorn). 
  • Sediment accretion along floodplains in New Zealand, North Island.  Case studies in collaboration with G. Brierley

 

 

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