Investigating decadal‐scale geomorphic dynamics in an alpine mountain setting

Abstract

We know little about the effect of recent climate variability upon landscapes at the timescale of decades because of (1) the complex, nonlinear, and path‐dependent nature of the response of a landscape to climate forcing and (2) the difficulty of quantifying spatially distributed impacts at the timescale of decades to centuries, despite this being the timescale over which significant hypotheses have been raised over human impacts upon climate change and hence geomorphic systems. A unique resource to investigate the linkages between climatic variability and geomorphic response is provided by the extensive coverage of aerial imagery commonly available since the 1950s. Here we use archival digital photogrammetry to produce high‐precision digital elevation models over large spatial scales, and so to reconstruct the quantitative history of surface downwasting and sediment flux in a high mountain alpine system, over the timescales of decades. Propagation of error methods is used to identify locations of significant landscape response and to compute volumes of significant surface change. Orthorectified aerial images are used in an image correlation framework to detect horizontal and vertical displacements of components of the landscape. Results are coupled to extant climate data and modeled snow cover to show how the landscape responds to climate forcing and to geomorphological maps to understand how this response varies between landscape elements. The results show distinct landscape response to both warming and cooling periods and a tendency for the acceleration of surface displacement under warming conditions. Precipitation and snow cover are critical in controlling glacier dynamics and rock glacier displacement velocities. However, while some landforms might lead to locally high sediment flux, landscape heritage can disconnect zones of high change rates from the valley bottom. Hence, the landscape response to climate forcing is not necessarily reflected in valley system processes or sediment deposits.

Internal Structure and Current Evolution of Very Small Debris-Covered Glacier Systems Located in Alpine Permafrost Environments

“…The investigated sites are located within permafrost areas, as shown by regional permafrost maps (BAFU, 2005;Bodin et al, 2008;Lambiel et al, 2009;Boeckli et al, 2012). The local occurrence of permafrost conditions was also shown in talus rock glaciers near les Rognes (Bosson et al, 2015; Figure 2) and Tsarmine Micheletti et al, 2015), or in frozen talus slopes near Entre la Reille (Reynard et al, 1999).…”

Proglacial sediment dynamics from daily to seasonal scales in a glaciated Alpine catchment (Bossons glacier, Mont Blanc massif, France)

“…According to the paraglacial concept, present-day proglacial areas could generate high sediment exports as sediments stored beneath glaciers or within moraines are transferred downstream (e.g., Gurnell et al, 2000). Proglacial zones are already known to react very dynamically to transient events as well as to variations in meltwater runoff, glacial terminus position and sediment supply (e.g., Staines et al, 2014;Micheletti et al, 2015;Delaney et al, 2017). Consequently, quantifying the change in sediment export from proglacial areas provides useful insights for understanding climate change implications for mass transfer from uplands to lowlands (e.g., Knight and Harrison, 2014;Heckmann et al, 2015) and for modelling changes in relief over geological time (e.g., Herman and Braun, 2008).…”

Temperature signal in suspended sediment export from an Alpine catchment

“…Glacier retreat discloses a large amount of sediments available to be transported by proglacial streams. Moreover, change in climatic conditions and specifically temperaturedriven glacier recession and permafrost degradation may initiate specific erosional processes that consequently enhance sediment supply in proglacial environments (Micheletti et al, 2015;Micheletti and Lane, 2016;Lane et al, 2016).…”

“…Huggel et al, 2012;Zerathe et al, 2014;Micheletti et al, 2015;Palazón and Navas, 2016;Wood et al, 2016). The premise behind this work is that to explain impacts of changes in climate on Alpine catchment suspended sediment yield, it is necessary to consider both transport capacity and sediment supply.…”