Professor Rolf Aalto

About me:

Office hours: Please sign up online for a meeting. By default meetings are on Teams, although you are welcome to meet in person -- please email me the day before if you want to meet in person (Amory C414), so that I can be sure to meet you there.

Rolf researches rivers and erosion across 6 continents, including: South America (Beni, Mamore, Orinoco & Ucayali Rivers), North America (Sacramento-CA, Feather-CA & Salmon-ID Rivers & Rio Grande-NM), Australasia (Strickland & Fly Rivers PNG), Europe (Danube River Romania), and Asia (Mekong River, Cambodia & exploratory sites in China). He leads the Exeter Radiometry Lab, which features world-class analytical facilities for tracing and dating particle movement throughout a wide range of fluvial dispersal systems. He develops field and laboratory techniques to quantify processes across a range of fluvial environments as well as application of modelling and remotely sensed data to field problems. His research projects include a Critical Zone Observatory (CRB-CZO), a NSF-Margins project studying fluvial and biogeochemical processes in Papua New Guinea, a NERC project investigating the evolution of the Beni River System in Bolivia, several NERC projects studying the evolution of the Mekong River, and a NERC project investigating the future of the Amazon River.

Rolf’s teaching focuses on the application of GIS, modelling, and laboratory methods to solving problems within River Basin Science. Students rate his modules highly, especially for 'development', and graduates report employability exceeding 90%.

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.

Personal Interests:

River basin processes in fluvial and hillslope geomorphology, especially: sediment and biogeochemical fluxes within fluvial dispersal systems, tropical rivers and their floodplains, sediment-associated carbon cycling, geophysical/sonar profiling of fluvial stratigraphy, and refining experimental techniques for dating, tracing, and characterizing the production and movement of fine sediment. Rolf's technical expertise relates to the analysis of a range of fallout radionuclides (210-Pb, 137-Cs, 10-Be, 7-Be) in sediment and soil, field surveys and sample collection in a range of challenging environments, various types of laboratory analyses of biogeochemical data from cores, geophysical measurements/analyses using advanced sonar and DPGS equipment in remote fluvial environments, and GIS analysis of spatial data (especially SRTM and ASTER).

Qualifications:

• Dual BA/BSc degrees in Geology (Honors) and Applied Mathematics (UC Berkeley)
• PhD and MSc, Geological Sciences (University of Washington)
• NASA Earth System Science Fellow and Post-Doc (U Washington)
• NSF Margins Post-Doctoral Researcher (UC Berkeley)
• Licensed Engineering Geologist and Licensed Geologist, Washington

Career:

Rolf obtained his undergraduate degrees from UC Berkeley, where he was inspired to study fluvial processes in a module taught by Prof. William Dietrich (at that time working in Papua New Guinea), completing an honors thesis studying floodplain sedimentation in a specially designed flume.

He completed a MSc degree at the University of Washington (Seattle), working with Prof. Thomas Dunne as a Research Assistant to calculate sediment fluxes along the Amazon River and writing a thesis on ”Discordance between suspended sediment diffusion theory and observed sediment concentration profiles in rivers.” Rolf was awarded a NASA Earth System Science Fellowship to pursue his research ambitions on tropical rivers followed by a major NSF research grant, culminating in his dissertation “Geomorphic Form and Process of Sediment Flux within an Active Orogen.”

Rolf then worked as a Post Doc at UC Berkeley, returning full circle to study fluvial processes in PNG. He was hired as Research Faculty at Washington with Prof. David Montgomery (a MacArthur 'Genius'), funded by a NASA Post Doctoral grant to investigate the SRTM dataset and a CALFED project on the Sacramento River. He was then promoted to Assistant Professor (he remains an Affiliate Associate Professor) at UW where he developed a laboratory and graduate program, wrote four successful NSF research proposals, and initiated new projects in Amazonia, Romania, California, PNG, Venezuela, Greenland, and SE Asia.

In 2007 Rolf joined Exeter’s internationally acclaimed River Basin Science group to further develop world-class analytical facilities for tracing and dating sediment movement throughout a wide range of fluvial dispersal systems. He collaborates extensively with Prof. Nicholas (physics-based models of large river systems), Prof. Quine (erosion and biogeochemical evolution of soils), and Dr. Aragao (vegetation and fire in the tropics). Rolf has also consulted professionally since 1995 on a range of topics related to geomorphic hazards and river restoration (as a Licensed Engineering Geologist). To date he has written/co-written successful research proposals worth >$10 million USD and led/co-led the execution of this research by diverse international & interdisciplinary teams working across a wide range of logistically challenging environments throughout the world.