Molards as an indicator of permafrost degradation and landslide processes

Costanza Morino,Susan J Conway,Þorsteinn Sæmundsson,Jón Kristinn Helgason,John Hillier,Frances E.G Butcher,Matthew R Balme,Colm Jordan,Tom Argles

doi:10.1016/j.epsl.2019.03.040

Abstract

Molards have been defined in the past as conical mounds of debris that can form part of a landslide's deposits. We present the first conclusive evidence that molards in permafrost terrains are cones of loose debris that result from thawing of frozen blocks of ice-rich sediments mobilised by a landslide, and hence propose a rigorous definition of this landform in permafrost environments. We show that molards can be used as an indicator of permafrost degradation, and that their morphometry and spatial distribution give valuable insights into landslide dynamics in permafrost environments. We demonstrate that molards are readily recognisable not only in the field, but also in remote sensing data; surveys of historic aerial imagery allow the recognition of relict molards, which can be used as an indicator of current and past permafrost conditions. The triggering of landslides as a result of permafrost degradation will arguably occur more often as global atmospheric temperatures increase, so molards should be added to our armoury for tracking climate change, as well as helping us to understand landslide-related hazards. Finally, we have also identified candidate molards on Mars, so molards can inform about landscape evolution on Earth and other planetary bodies.

Highlights

Glacial and periglacial environments are sensitive to the effects of climate change (Haeberli and Beniston, 1998; Hinzman et al, 2005)
During the field observations performed immediately after the failures, in the Móafellshyrna landslide deposits we found isolated pseudo-cubic and angular blocks of ice-rich sediments (Fig. 2a, e) that came to rest at the foot of the talus slope where the topography flattens (Fig. 2a), 295-390 m below the source area (Fig. 3a)
By studying how the deposits of two landslides in northern Iceland evolved through time, we have shown for the first time that molards in permafrost terrains are cones of loose debris that result from the degradation of blocks and ridges of ice-cemented deposits mobilised by landslides

Summary

Introduction

Glacial and periglacial environments are sensitive to the effects of climate change (Haeberli and Beniston, 1998; Hinzman et al, 2005). Molards have been defined as conical mounds occurring in landslide deposits (Brideau et al, 2009; Cassie et al, 1988; Cruden, 1982; Geertsema et al, 2006b; Goguel and Pachoud, 1972; Jermyn and Geertsema, 2015; Lyle et al, 2004; McConnell and Brock, 1903; Milana, 2016; Mollard and Janes, 1984; Xu et al, 2012). Molards have been found in the distal zones, at the margins of the displaced mass, and/or below the main scarp of landslides (Cruden, 1982; Geertsema et al, 2006b)

Methods

Results

Discussion

Conclusion