In the past years, it has become apparent that human activities are increasingly affecting the surface of the Earth. Extreme meteorological events are becoming the new norm, and changes in the climatic drivers of Earth surface processes are pushing the study of geomorphology towards new frontiers. Since several millennia, human activities are causing large changes in ecosystems, land use, hydrological routing, and direct anthropogenic modification of the landscape by construction. These changes impact systems across the full spectrum of geomorphology. A key challenge in the coming years is to translate our understanding of geomorphic processes, which is often based on observations of past or current conditions, into the rapidly changing future.
This session will bring together a series of invited speakers to provide insights and perspectives in this topic from across the field of geomorphology.

Convener: Kristen Cook | Co-conveners: Annegret LarsenECSECS, Giulia Sofia, Matteo Spagnolo, Andrea Zerboni
| Attendance Wed, 06 May, 10:45–12:30 (CEST)

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Chat time: Wednesday, 6 May 2020, 10:45–12:30

D987 |
| Highlight
| GM Division Outstanding ECS Lecture
Georgina Bennett

Mountain landscapes are beautiful, yet hazardous, and vulnerable to climate change and population growth. Not only is the study of these landscapes geomorphically captivating, but it is increasingly relevant to society. Three Grand Challenges in the study of processes, landscapes and hazards in mountain regions are (1) Understanding and predicting the response of earth surface processes to climate (2) Monitoring and early warning of extreme events such as landslides and floods and (3) Accounting for connectivity and feedbacks between hillslopes and channels in landscape evolution and hazards. We need a suite of tools and approaches to address these challenges. Harnessing the growing archive of satellite and aerial photography helps us to study landscape dynamics and response to drivers such as climate over large regions. Innovative sensor technology is needed to understand landscape dynamics at a finer scale and to develop real time warning of extreme events. Finally, we need conceptual models that capture the essence of landscape dynamics and help to forecast hazards as they slide, flow, rock and roll through the landscape.

How to cite: Bennett, G.: Sliding, flowing, rocking and rolling: Sediment and hazard cascades through mountain landscapes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4726, https://doi.org/10.5194/egusphere-egu2020-4726, 2020

D988 |
Stuart Lane

The Anthropocene is widely described as producing a rupture in the global stratigraphic signature, attributable to human activities. There is no doubt that human activities have introduced new products into the stratigraphic record; and that humans are modifying the geomorphic processes that produce the sediment which then becomes incorporated into that record. The stratigraphic literature is replete with simplistic generalisations of how sediment flux to the continental shelf is changing, such as increasing due to soil erosion or decreasing due to hydropower related sediment flux disconnection. Here we argue that human impacts on geomorphic processes in the Anthropocene are unlikely to be stationary for long enough for them to be seen consistently across the depositional record of many different environments. Illustrating this for a major inner-Alpine drainage basin, the Swiss Rhône, we show that human-driven global climate-change is indeed dramatically altering the geomorphic process regimes of Alpine environments. However, there are three broad reasons why this is unlikely to be seen in the future geological record. First, the geomorphic response that drives increased sediment delivery is transient because of the significant regime changes associated with global climate change impacts. Second, such increases are countered by other human impacts, notably those on sediment flux, which are tending to reduce the connectivity of sediment sources to downstream sediment sinks. Third, human impacts on both sediment sources and connectivity are nonstationary, driven by both exogenous factors (here illustrated by the worldwide economic shock of 2008) and endogenous ones, notably human response to the perceived problems caused by both sediment starvation and sediment over-supply. In geomorphic terms, then, there is a difference between the pervasive nature of Earth system shifts that we see in the pre-Holocene depositional record and the more ephemeral impacts of the Earth system – human coupling associated with the Anthropocene. The extent to which this is the case is likely to vary geographically and temporally as a function of the degree and nature of human impacts on geomorphic processes. Thus, the primary challenge for future prediction will be as much the prediction of the complex and reflexive nature of human response as it will be geomorphic processes themselves.

How to cite: Lane, S.: Will human impacts on Alpine geomorphic processes scale up to the depositional record?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13018, https://doi.org/10.5194/egusphere-egu2020-13018, 2020

D989 |
Larissa Naylor, Jim Hansom, Douglas Mitchell, James Fitton, Freya Muir, Martin Hurst, and Alastair Rennie

Geomorphology has much to contribute to the understanding of how geomorphic landscapes have responded to climatological extremes and will likely respond in the future. These contributions can be in terms of systems dynamics and their past, present and likely future responses to sudden events, tipping points or more gradual changes to natural landforms and anthropogenic structures. However, equally importantly, geomorphic contributions also include making proactive resilience and climate change adaptation decisions in order to create physical space for geomorphic systems to respond more naturally and dynamically to extremes – now or in the near (100 year) future. The choices society makes in the present – such as planning, infrastructure and engineering decisions – have a strong bearing on the physical space left to allow natural landforms to adjust to extreme events while minimizing social and economic impacts. This creates a new frontier for geomorphology science at the social, political and policy interface.  Interesting questions arise in this space, such as: How much do we expect a geomorphic system to respond dynamically to extreme forcing? i.e. How much physical space do we [planners] need for the system to respond to an extreme event? Should society see storms as catalysts for proactive adaptation? How much (physical space, i.e. geomorphic accommodation space) can we allow when realigning road or rail inland to reduce risk in future storm events? How do complex physical geomorphic systems interact with complex urban systems? Can we work with artists, landscape architects, geo-spatial, urban and social scientists to create transformative, systems-based adaptation scenarios to allow us to better live in an era of extremes? Geomorphologists are usefully contributing to improving the resilience and/or limiting deterioration or habitat loss (e.g. habitat squeeze due to sea level rise) in urban ecosystems and anthropogenic structures.  This includes geomorphic contributions to nature-based solutions, green infrastructure and the resilience of traditional engineering to extreme events.  This paper highlights some of the opportunities we have to influence and shape our future resilience to extreme events – in the present day – through interdisciplinary research and socio-geomorphology practice. We need to create windows of opportunity now for more dynamic and resilient geomorphic futures.  

How to cite: Naylor, L., Hansom, J., Mitchell, D., Fitton, J., Muir, F., Hurst, M., and Rennie, A.: Re-imagining urban coasts: a socio-geomorphology lens to enhance life in an era of extremes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20334, https://doi.org/10.5194/egusphere-egu2020-20334, 2020

D990 |
Guido Grosse, Julia Boike, Louise Farquharson, Benjamin M. Jones, Moritz Langer, Hugues Lantuit, Anna Liljedahl, Ingmar Nitze, Alexandra Runge, Vladimir E. Romanovsky, Thomas Schneider von Deimling, Warwick F. Vincent, and Donald A. (Skip) Walker

In this presentation, we will highlight some of the overarching geomorphic dynamics of gradual and abrupt permafrost thaw using examples from Siberia, Alaska, and Canada, their role in Arctic landscapes transitioning to a warmer world, and implications for the Earth System. Northern high latitude regions are particularly vulnerable to warming and changes in climatic patterns, which leads to the thaw of ice-rich permafrost across vast Arctic and sub-Arctic landscapes. Permafrost thaw and subsequent geomorphological change directly interact with hydrology, biogeochemistry, and biology and thus have been major agents of Arctic ecosystem change since the last deglaciation. The changes are also important contributors to cumulative impacts associated with historic and current development of the Arctic, including in association with infrastructure. Today, in a rapidly warming Arctic, permafrost thaw processes, both gradual and abrupt, are accelerating in a manner comparable to the Holocene Thermal Maximum. At the same time, other environmental forcing factors, such as wildfires, precipitation, and hydrological processes, are also changing, either further reinforcing thaw dynamics or enhancing drainage and stabilizing the ground. Many of the resulting gradual and abrupt thaw processes are non-linear. Their dynamics are still poorly understood and insufficiently quantified in large-scale models due to lacking or limited representation of water-ice phase transitions during freeze-thaw cycles, ground ice distribution and loss, and challenging implementation of sub-gridcell scale interactions between frozen ground and hydrology. Gradual thaw impacts are especially pronounced in regions with an abundance of ice wedge polygons, and include changes in microtopography and extensive ponding in natural landscapes and those adjacent to infrastructure, where soils are warmed due to increased dust, flooding, snowdrifts, and altered vegetation. Abrupt thaw processes such as thermokarst and thermo-erosion represent rapid dynamics that are widespread in Arctic lowlands but poorly represented in observations and models. Characteristic landforms that result from abrupt thaw include thermokarst lakes and basins, retrogressive thaw slumps, and steep coastal bluffs. These landscape changes may be triggered by climate-driven press disturbances such as sea ice loss or increases in precipitation, pulse disturbances such as wildfires, or by anthropogenic disturbances such as road construction. When loss of excess ground ice is involved, positive feedbacks can result in a decoupling of further geomorphological change from climate. Once initiated, this may lead to continued or even accelerated growth of such features under a wide range of climate conditions, including in the high Arctic. Most abrupt thaw processes produce lasting impacts on northern permafrost landscapes that are irreversible over millennial timescales and result in the short-term mobilization of large amounts of permafrost carbon that may further contribute to climate warming.

How to cite: Grosse, G., Boike, J., Farquharson, L., Jones, B. M., Langer, M., Lantuit, H., Liljedahl, A., Nitze, I., Runge, A., Romanovsky, V. E., Schneider von Deimling, T., Vincent, W. F., and Walker, D. A. (.: Gradual and Abrupt Permafrost Thaw as Drivers of Rapid Geomorphic Change in Arctic Permafrost Regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11772, https://doi.org/10.5194/egusphere-egu2020-11772, 2020

D991 |
| Highlight
Eliisa Lotsari

Global climate change is driving rapid changes in polar region, and significant attention has been given to predicting changes in precipitation and hydrology. However, warming will also alter sediment dynamics and drive morphological change as the melting of river and ground ice will mobilise floodplain and river channel sediments. The transport of this additional sediment can have a number of direct and indirect impacts on societies and ecosystems with yet unpredictable magnitude. There is a significant knowledge gap concerning how material is transported seasonally across such zones, and how the frozen season at present and its possible future changes affect the hydro- and morphodynamics of these northern rivers.

Therefore, it is needed 1: To determine the impacts of varying river ice processes on seasonal hydrodynamics, sediment transport, and flood hazards in the high north; 2: To define the seasonal interlinkages and combined effects of sub-aerial (e.g., freeze-thaw, mass movements) and fluvial processes (e.g., ice-covered/open-channel flow) on morphodynamics, sediment transport and its origin in these seasonally ice-covered river systems. 3: To upscale reach scale seasonally-driven river morphodynamics to the watershed scale and simulate changes into the future, whilst defining the feedbacks between defrosting watersheds and total sediment load transported to the oceans.

This work is yet to be done, however, preliminary results are presented based on gathered pilot data and studies. Recent results have revealed that river ice can have the most significant role, greater than that of flowing water, in erosion and transport of coarse sediment from a sub-arctic river channel bed and its gently sloping banks. In addition, the findings from sandy meandering river suggest that certain ice cover conditions cause the vertical and lateral flow distribution to be opposite to the open channel situation. Thus, future changed river ice cover characteristics are expected to change these transport mechanisms and velocity distribution. This emphasizes that future predictions of river ice are needed, before predicting the changes in river morphology. However, it has been recently shown that thermal ice growth equation is not expected to work in the polar region in the future, as there is expected to be less snow and a higher number of freeze-thaw days in the future. In addition, adjustments to the ice decay equation and the applied parameter values would be needed for predicting ice decay processes in future. Under fast climatic warming of the arctic and subarctic, the shortening frozen period may also induce an earlier and prolonged season of bank erosion in meandering rivers, which further complicates the predictions of river morphodynamics. Thus, the use of improved hydro- and morphodynamic models and high-accuracy spatial and temporal data for better calibrating these models, are essential for detecting seasonally varying feedback effects of different interacting processes on river hydro-morphodynamics at present and in the future.

How to cite: Lotsari, E.: Impacts of frozen season and its possible future changes on the hydro- and morphodynamics of northern rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5719, https://doi.org/10.5194/egusphere-egu2020-5719, 2020

D992 |
Cathelijne Stoof

Climate change is expected to alter fire regimes but also rainfall patterns. Fire is a natural process that removes vegetation and may affect soil properties, resulting in changes in overland flow and streamflow generation. Some fires cause erosion and may even cause destructive debris flow and other events, which can not only threaten lives and property but also leave lasting imprints in landscapes. The geomorphological response after fire events is a complex function of pre-fire landscape and vegetation properties, fire behavior and effects, and post-fire rainfall timing, duration and intensity. In this talk, I highlight these processes using examples of past events, and explore geomorphological response to fires in a future where both fire and rainfall may be be rather different.


How to cite: Stoof, C.: Fire effects on geomorphology: what can we expect with climate change?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18260, https://doi.org/10.5194/egusphere-egu2020-18260, 2020