28 Feb 2022
28 Feb 2022
Status: this preprint is currently under review for the journal NHESS.

What drives landslide risk: Disaggregating risk analyses, an example from the Franz Josef and Fox Glacier Valleys, New Zealand

Saskia de Vilder1, Chris Massey1, Biljana Lukovic1, Tony Taig2, and Regine Morgenstern1 Saskia de Vilder et al.
  • 1GNS Science, Lower Hutt, 6012, New Zealand
  • 2TTAC Ltd, Cheshire, CW9 6EU, United Kingdom

Abstract. We present a quantitative risk analysis (QRA) case-study from the Franz Josef and Fox Glacier Valleys, on the West Coast of the South Island, New Zealand. The Glacier Valleys are important tourist destinations that are subject to landslide hazards. Both valleys contain actively retreating glaciers, experience high rainfall, and are proximal to the Alpine Fault, which is a major source of seismic hazard on the West Coast. We considered the life safety risk from rockfalls, soil/rock avalanches and flows that are either seismically triggered or occur aseismically. To determine the range in risk values, and dominant contributing variables on the risk, we modelled nine different risk scenarios where we incrementally changed the variables used in the risk model to account for the underlying uncertainty. The scenarios represent our central estimate of the risk, e.g. neither optimistic nor conservative, through to our upper estimate of the risk. We include in these estimates the impact of time-variable factors, such as a recently reactivated landslide has had on locally increasing risk and the time-elapsed since the last major earthquake on the nearby Alpine Fault. We disaggregated our risk results to determine the dominant drivers in landslide risk, which highlighted importance of considering dynamic time variable risk scenarios and the changing contributions to risk from aseismic versus seismic landslides. A detailed understanding of the drivers of landslide risk in each valley is important to determine the most efficient and appropriate risk management decisions.

Saskia de Vilder et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'RC Comment on nhess-2022-57', Nicolas Barth, 15 Mar 2022
    • AC1: 'Reply on CC1', Saskia de Vilder, 29 Mar 2022
  • RC1: 'Comment on nhess-2022-57', Tom Robinson, 30 Mar 2022
    • AC2: 'Reply on RC1', Saskia de Vilder, 18 May 2022
  • RC2: 'Comment on nhess-2022-57', Caroline Orchiston, 06 Apr 2022
    • AC3: 'Reply on RC2', Saskia de Vilder, 18 May 2022

Saskia de Vilder et al.

Saskia de Vilder et al.


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Short summary
This study calculates the fatality risk posed by landslides while visiting Franz Josef and Fox Glacier valleys, New Zealand for nine different scenarios, where the variables of the risk equation were adjusted to determine the range in risk values and associated uncertainty. The results show that it is important to consider variable inputs that change through time, such as the increasing probability of an earthquake and the impact of climate change on landslides characteristics.