Mobility and dynamics of Giant landslides

TL;DR

This study investigates the dynamics and causes of a large ancient landslide in Tahiti, using modeling to determine it was likely caused by a few high-velocity events under submarine conditions, with implications for understanding such rare phenomena.

Contribution

It provides new insights into the number of events and velocity of a giant landslide, highlighting the role of submarine conditions in its dynamics.

Findings

Single or few events caused the landslide.

Maximum slide velocity exceeded 125 m/s.

Submarine propagation led to slower but longer runout.

Abstract

The rarity of large landslides reduces the number of observations and hinders the understanding of these phenomena. Runout distance was used here to determine whether the large landslide deposit formed several thousand years ago in northern Tahiti was caused by a single or multiple events. Using modelling to quantify the dynamics of this event suggested that a single event or a small number of events (n<10) were responsible, and that the maximum slide velocity was high (>125 m/s) under partially submarine conditions. Such submarine propagation favoured a slower dynamic but a longer runout. The effective basal friction under submarine conditions ranged from 0.2 < $\mu$ < 0.3.