Understanding the influence of sediment dynamics on postglacial landscape evolution

Informations projet

POSTCOLD

N° de convention de subvention: 101064307

DOI

10.3030/101064307

Projet clôturé

Date de signature de la CE 7 Juin 2022

Date de début 15 Juin 2022

Date de fin 14 Decembre 2023

Financé au titre de

• Marie Skłodowska-Curie Actions (MSCA)

Coût total

Aucune donnée

Contribution de l’UE

€ 130 385,52

Coordonné par

GFZ HELMHOLTZ-ZENTRUM FUR GEOFORSCHUNG
Germany

Periodic Reporting for period 1 - POSTCOLD (Understanding the influence of sediment dynamics on postglacial landscape evolution)

Période du rapport: 2022-06-15 au 2023-12-14

Résumé du contexte et des objectifs généraux du projet

Repeated glacial-interglacial cycles during the last 2.6 million years have significantly impacted the topography of many mountain ranges around the world. Yet, the response of landscape evolution to repeated climate oscillations has not been well quantified. In recently deglaciated landscapes, the transition from glacial to fluvial/hillslope processes have induced progressive topographic adjustments, and the large amounts of sediments inherited from glacial periods and generated through landsliding of oversteepened glaciated topography may act as a fundamental control on the incision of postglacial rivers. These sediments can enhance fluvial incision rate by providing more tools for erosion, or inhibit incision by armoring the river bed. Characterizing when and where sediment enhances or inhibits fluvial incision in postglacial landscapes is critical for understanding the response of mountain topography to deglaciation. The main scientific objectives of POSTCOLD were 1) to develop a landscape evolution model to account for the complex impact of sediment dynamics on fluvial incision in postglacial landscapes and 2) to investigate the response of fluvial incision to changes in sediment supply and assess the effects of sediment on postglacial landscape evolution. The results of POSTCOLD provide a quantitative understanding of postglacial fluvial incision histories, which is critical for ecosystem management and natural hazard assessment in recently deglaciated mid-latitude mountain ranges and perhaps in high-latitude mountain ranges where continued climate change may eventually lead to deglaciation.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

1. Various landscape evolution models have been developed to account for the coevolution of alluvial cover and sediment-flux-dependent bedrock incision. We compare the two most commonly used models for sediment transport: an Exner-type model and an erosion-deposition model, to see how their predictions of long-term postglacial river incision rates differ. We found that, even though the two models aim to mimic the same scenarios, they predict that rivers will erode at much different speeds when sediment is occasionally dumped into the river. In particular, the erosion-deposition model short sediment transport length can capture the behavior of the Exner-type model and thus has a wider applicability than the Exner-type model.

2. We have combined the erosion-deposition model with the saltation-abrasion model for sediment and built a one-dimensional river profile model. Using this model, we have run a group of simulations to investigate the impact of sediment on knickpoint retreat rate in postglacial rivers. The results indicate that the knickpoint retreat distance is controlled by the accumulated amounts of sediments delivered to the river.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

This project integrates recent advances in understanding the sediment dynamics and sediment-flux-dependent river incision and opens new possibilities to quantify the complex impact of sediment flux on postglacial river incision rates. Our comparison of the erosion-deposition model and Exner-type model highlights the importance of sediment transport length, suggesting that in order to validate models of sediment-flux-dependent river evolution, future research should focus on constraining the value of sediment transport length. Additionally, our results reveal a testable relationship between the knickpoint retreat distance (thus the response timescales) and the total amount of sediments transported by the river. Future research should test this relationship, and this finding can help us understand the evolution of basins with different sediment regimes in the Alps and other glaciated mountain ranges.

A river gorge incising into the U-shaped glacial valley shows the transient adjustment in topography