Section 5.1: Geomorphology

Because Earth surface dynamics depend on so many internal and external processes and their interactions, it is important to develop a holistic approach, pursuing geomorphology within a comprehensive, multi-disciplinary framework and with an eye on resolving all major processes on matching spatial and temporal scales. The research group does this with specific attention to five broad themes that encompass many of the challenges listed above. These themes are:

Principal aim: Resolve mechanisms, patterns and rates of erosion, their controls, and their role in landscape evolution to enable interpretation of the landscape as a record of past environmental change, to predict effects of future environmental and climate change, and to evaluate and mitigate natural hazard risk.

In this theme we are concerned with the mechanics of glacial, aeolian and marine erosion on hillslopes and in river channels, and the mathematical representation of these processes. In addition, established and novel techniques are used to quantify shallow exhumation and denudation over a range of time scales, in support of observational studies of landscape dynamics. These techniques will include optically stimulated luminescence thermo-chronometry (OSL) and Raman spectroscopy in addition to thermochronometric and geochemical approaches. Observational insights are combined with theoretical considerations and numerical and physical modelling to advance understanding of the erosional evolution of topography. This theme, within the heartland of Geomorphology, provides an anchor and forum for other, inter-disciplinary activities of the group.

Principal aim: To identify and constrain the mechanisms by which erosion influences Earth’s Carbon Cycle.

The erosion-aided geological draw down of CO2 is essential to the relative stability of Earth’s climate on long time scales that has permitted emergence of life and evolution of complex organisms. Moreover, burial of erosionally sourced organic carbon contributes to the formation of hydrocarbon deposits in predictable locations and quantities. The group explores the natural pathways via which CO2 is exchanged between Earth’s atmosphere and geological repositories. Emphasis will be on...

  • weathering in surface and subsurface reservoirs,
  • biological mediation of rock mass disintegration and weathering,
  • transfer of organic carbon to soils,
  • the role of soil erosion and landsliding,
  • the delivery of organic carbon to geological depocentres, and
  • the preservation of organic carbon in geological storage.

An explicit target of research in this area is to quantitatively constrain the carbon mass budget of an active orogenic system in the first instance, and other major tectonic units thereafter. The group also works on the integration of dissolved inorganic and particulate organic carbon fluxes in numerical models of landscape dynamics in order to enable detailed explorations of scenarios involving geomorphic, climatic or tectonic change over longer time scales.

Projects:

Principal aims:

  1. Constrain the links between geophysical processes such as earthquakes and the geomorphic processes they trigger in order to explain and anticipate patterns of mass wasting during and after earthquakes (responsible for half of all fatalities due to earthquakes in mountain areas) and use these patterns to study earthquake mechanisms where detailed instrumental records are absent (most places).
  2. Revolutionize monitoring of surface processes by application of seismological techniques, overcoming severe limitations in time-resolution of air- and space-borne remote sensing that obstruct understanding of the link between meteorological drivers and erosional response.

The group develops two major and distinct research efforts within this theme. One focuses on seismically induced erosion, aiming to predict patterns of triggered landsliding from earthquake mechanisms and models of seismic wave propagation; to invert observed erosion patterns for insights into seismic processes; and to constrain orogen mass balances on seismic cycle scales. The other focuses on development of a seismological approach to monitoring of geomorphological processes, and its application in studies of process mechanics and landscape response to changing boundary conditions. This approach uses the acoustic signals of mass transport at the Earth’s surface to determine the location, timing, magnitude and nature of geomorphic process events. Unlike any other remote sensing technique, it has a temporal resolution that allows the evaluation of geomorphic activity in the context of meteorological conditions. Therefore, it is the key to understanding landscape response to climate change, as well as many other aspects of earth surface dynamics.

Projects:

Principal aim: Determine how climate (precipitation, temperature), and its variability and change govern the dynamics of Earth surface processes and affect the natural landscape and the human habitat.

The group uses numerical modeling and observational approaches. Surface process and landscape evolution models are combined with local scale climate models to investigate the geomorphic impacts of climate variability and change on time scales ranging from decades to millions of years. Output of these models is tested against digital models of topography with known history of climatic forcing, depositional records of landscape erosion obtained for example by cosmogenic nuclide analysis of terrace, delta or lake bed sediments, and direct observation of erosion fluxes in the context of weather records. In this work, special attention is paid to the roles of temperature and temperature variations, and of climate-dependent biological and chemical processes, which are often neglected in considerations of climate-driven landscape dynamics.

Projects:

Principal aim: Resolve how signals of erosion get transmitted, integrated, altered, and shredded in sediment transport and deposition systems, and to provide a rationale for inversion of basin stratigraphy for insights into the compound impacts of environmental change in uplands over longer time scales.

Sediments in geological basins record the conditions of sediment production and deposition. Therefore, basins can contain long and relatively complete records of environmental change. Sedimentary archives have been used very successfully for reconstruction of Earth’s climate history, but they can also contain information about erosion of the continents under past climates and climate changes. The decoding of these paired records can add significantly to our ability to understand today’s Earth surface dynamics and to anticipate the geomorphic response to ongoing and future climate change. Robust use of sedimentary archives for study of continental erosion and its response to tectonic and climatic changes requires a quantitative understanding of the downslope transmission of erosion signals. The group uses hydrometric, geophysical and geochemical techniques combined with numerical modeling to quantify and track sediment fluxes through sediment routing systems from upland sources to terrestrial and oceanic depocentres. Emphasis is placed on transfer of sediment between distinct process domains, and mechanisms of temporary sediment storage and remobilisation.

Projects:

Although it is legitimate to develop focused research efforts targeted on these individual themes, there is unique value in their integration. Concepts, constraints, methods and approaches obtained within one theme are essential to addressing other themes effectively, with the potential for further links and feedbacks. As an example, seismic monitoring of geomorphological activity in upland catchments can give insights into the exact meteorological conditions that cause surface process events, enhance predictive understanding of landscape response to climate change, and allow natural hazard risk assessment and early warning. It will also underpin a detailed evaluation of the links between the physical, chemical and biological processes that drive geological draw down of CO2, when paired with downstream measurements of sediment and dissolved loads of rivers. This could give rise, amongst others, to rare insight into the role of geomorphological processes in ecosystem dynamics. The notion that this integration requires pursuit of multiple themes in tandem and the application of a range of techniques and approaches is central to the group’s research strategy.