Denudation rates during a postglacial sequence in Northern Iceland: example of Laxárdalur valley in the Skagafjörður area

ABSTRACT

For several decades, geomorphologists have focused on the functioning of geomorphic systems after deglaciation. The relative importance of paraglacial vs. periglacial processes has been highly debated. At present, the development of dating techniques allows to contribute to this debate. We reconstruct in this paper the geomorphic evolution of Tindastóll mountain slopes in Laxárdalur valley (Skagafjörður area, central northern Iceland), where a chronological framework can be established through tephrochronology and an assemblage of dated raised beaches. Volumetric calculations of constructed and excavated landforms were created from field data and from DEM and geographical information system techniques. Collectively, our data exhibit a first stage of paraglacial landsliding during the first half of the Holocene, followed by a stage of scree and rockglacier development (during the second half of the Holocene, but before 1100 AD). Our estimations indicate that more than 85% of the total sediment production were due to rock slope failure, and the rate of bedrock denudation due to periglacial processes was about one half of the rate of paraglacial processes. Nevertheless, paraglacial and periglacial processes cannot be seen here as antagonistic processes: they are organized in a sequence during which periglacial processes are conditioned (enhancement of bedrock denudation rates) by fracturing and consequent mass wasting. Screes and concomitant rockglaciers were indeed preconditioned by the landslide, while areas non-affected by landslides have remained mostly intact, characterized by a very low rate of accumulation due to geomorphic (periglacial) activity.

KEYWORDS:

• Paraglacial
• periglacial
• landslide
• rockglacier
• denudation rates
• slope
• Holocene

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Etienne Cossart is Professor at Université de Lyon (France). He defended a PhD on the geomorphic impacts of paraglaciation in French Alps, before working on the interaction between hillslope processes and fluvial streams in the Himalayas and in Iceland.

Denis Mercier, PhD, is Professor of physical geography at Paris-Sorbonne University. His research areas include paraglacial geomorphology in Iceland and Svalbard and natural hazards (marine flooding). He served as secretary of the French geomorphological group during six years. He is editorial member of the journal Geomorphology (Elsevier) and the journal Géomorphologie: relief, processus, environnement (GFG ed.). His recent books include “Géomorphologie de la France” (2013 Dunod ed.) and “Géomorphologie paraglaciaire” (2011, Editions Universitaires Européennes) and numerous papers in international peer-reviewed journals.

Julien Coquin defended a PhD Thesis on geomorphic paraglacial processes in Iceland.

Armelle Decaulne received her doctorate in geomorphology from University Blaise Pascal, France, and is a senior scientist at CNRS, in Nantes. Her research areas include slope dynamics since the deglaciation in high latitude cold environments (Iceland, Norway, Nunavik) and mid-Europeans mountains (massif Central, meridional Carpates and Pirin), with focus on slope development rates and natural hazards and risks.

Thierry Feuillet is an Associate Professor at the University of Paris 8 (France). He defended a PhD on the topic of periglacial geomorphology in the Pyrenees range. His current research areas focus on the quantitative spatial analysis of geographical phenomena.

Helgi Páll Jónsson worked on tephrochronology in northern Iceland and is now teaching earth sciences in Iceland.

Þorstein Sæmundsson focused on quaternary geochronology in Iceland, and is teaching earth sciences in Iceland.