Download Lithological control on landscape morphology and evolution

Lithological control on landscape morphology and evolution
Supervisors: Dr Mikaël Attal, Dr Simon Mudd and Prof. Hugh Sinclair
University of Edinburgh ([email protected])
Background: The nature of rocks exposed at the surface of the Earth exerts a primary control
on the shape of landscapes1. This is a very well-known fact: people are generally aware that
more resistant rocks tend to “stick out” in landscapes and are more likely to form steep slopes
than poorly resistant rocks (Fig. 1). However, whereas many studies have showed the
importance of rock type in controlling the morphology of rivers and hillslopes at a local scale 13
, very few have attempted to define the influence of bedrock properties on the temporal
evolution of landscapes as they respond to tectonic or climatic change.
Research questions and methods: In this study, we will combine numerical modelling with
the study of a series of sites where strong contrasts in lithology are known to influence
landscape morphology to define how changes in bedrock property (rock strength, grain
cohesion, joint density, orientation of bedding / joints) affect the geometry of rivers (slope,
width, roughness, % exposed bedrock) and hillslopes (steepness, curvature, % exposed
bedrock). Using the sites as templates, we will develop numerical modelling experiments to
define the role that generic changes in bedrock properties play in enhancing / delaying the
propagation of environmental signals through landscapes and therefore in driving competition
between eroding catchments. The study sites include the Rio Alias capture site in Southern
Spain4 and the Daluis Gorge in the Southern Alps (France) (Fig. 2).
Figure 1: The Zagros Mountains in Iran exemplify the influence of lithology on landscape
morphology (slope steepness, valley width, river planform). This “terrain” image (from Google
Map) shows ridges and valleys resulting from contrasts in resistance to erosion in an area
where rocks are folded and faulted (orientation of structures WNW-ESE).
Figure 2: The Daluis Gorge (SE France). As the Var River flows from limestone (left) to red
pelites (right), it undergoes spectacular morphological changes. The change in lithology affects
the shape of the landscape, with implications for the propagation of environmental signals from
rivers to hillslopes (bottom up processes) and for sediment delivery from hillslopes to
sedimentary basins (top down processes). Photos from Wikipedia.
Timetable: Year 1 – familiarisation with the topic and methods to be used (topographic
analysis, fieldwork, numerical modelling of landscape evolution), topographic analysis of the
study sites, collection of field data at the Spain site in spring. Year 2 – analysis of data, running
first set of numerical modelling experiments, collection of field data at the Alps site in spring.
Year 3 – Numerical modelling, analysis of field and numerical results, writing up. Throughout
year 2 and 3: paper writing and conference attendance.
Training and Requirements: A comprehensive training programme will be provided
comprising both specialist scientific training and generic transferable and professional skills.
The student will be trained in fluvial and tectonic geomorphology within the Land Surface
Dynamics group which currently includes ~10 PhD students and a postdoc. They will acquire
skills in the field (geomorphic surveying) and will use computer-based methods for topographic
analysis and numerical modelling. Numerical modelling will represent an important part of the
project so the student must be numerate and ideally familiar with computing languages such
as c++ and python. Understanding of basic geomorphology concepts is desirable but not
compulsory. The student will present their results at a number of national and international
conferences from year 2 on.
References:
[1] Wohl and Merritt. 2001. Bedrock channel morphology, Geol. Soc. Am. Bull.,
DOI:10.1130/0016-7606(2001)113<1205:BCM>2.0.CO;2.
[2] Chittenden et al. 2014. The influence of bedrock orientation on the landscape evolution,
surface morphology and denudation (Be-10) at the Niesen, Switzerland, Earth Surf. Proc.
Land., DOI:10.1002/esp.3511.
[3] Hurst et al. 2013. Influence of lithology on hillslope morphology and response to tectonic
forcing in the northern Sierra Nevada of California, J. Geophys. Res., doi:10.1002/jgrf.20049.
[4] Maher and Harvey. 2012. Interaction between the controls on fluvial system development:
tectonics, climate, base level and river capture – Rio Alias, Southeast Spain, Earth Surf.
Process. Landforms DOI:10.1002/esp.3247.
Summary: This project combines numerical modelling with fieldwork to define the influence of
rock type on the form and temporal evolution of landscapes in response to environmental
change.