Mineralogical and physico-chemical properties of halloysite-bearing slip surface material from a landslide during the 2018 Eastern Iburi earthquake, Hokkaido

Jun Kameda

doi:10.1186/s40645-021-00428-5

Abstract

Destructive landslides were triggered by the 6.7 Mw Eastern Iburi earthquake that struck southern Hokkaido, Japan, on 6 September 2018. Heavy rainfall on 4 September in addition to intermittent rainfall around the Iburi Tobu area saturated and weakened the slope-forming materials (mostly altered volcanoclastic soils), making them susceptible to failure because of the earthquake’s strong ground motion. Most of the shallow landslides exhibited long runouts along gentle hill slopes, with characteristic halloysite-bearing slip surface at the base of the volcanic soils. This study investigated the mineralogical and physico-chemical properties of the slip surface material with the aim of understanding weakening and post-failure behaviors during the landslides. Halloysite in the slip surface had irregular-to-hollow-spherical morphology with higher mesopore volumes than tubular halloysite, which is related to a high capacity for water retention after rainfall. To reproduce possible chemical changes in the slip surface during rainfall, the sample was immersed in varying amounts of rainwater; solution pH increased and ionic strength decreased with increasing water content. These findings, alongside electrophoretic analysis, suggest that rainwater infiltration could have increased the absolute zeta potential value of the slip surface material. It is suggested that rainfall before the earthquake enhanced the colloidal stability of halloysite particles within the slip surface, owing to an increase in electrostatic repulsion. This decreased the material’s cohesive strength, which might have led to destabilization of the slope during ground shaking generated by the earthquake, and subsequent high-mobility flow after failure.Irregular-to-hollow-spherical halloysite on the slip surface of a shallow landslide triggered by the 6.7 Mw Eastern Iburi earthquake. Rainfall before the earthquake enhanced electrostatic repulsion of halloysite particles (owing to solution pH increase and ionic strength decrease), which might have led to destabilization of the slope.

Highlights

IntroductionKluger et al (2017) observed halloysite with a unique morphology in a tephra layer involved in a flow slide and suggested that weak interparticle interactions contributed to the high sensitivity of the material
The Eastern Iburi earthquake (Mw = 6.7) occurred at 3:07 AM on 6 September 2018 in southern Hokkaido, Japan (Fig. 1a)
3.5 Immersion of the slip surface material in distilled water and rainwater To simulate possible changes of the solution chemistry of pore water within the slip surface during rainfall, dried bulk samples were immersed in rainwater and distilled water (FUJIFILM Wako Pure Chemicals Co.) at different solid/water weight ratios (S/W) for 24 h

Summary

Introduction

Kluger et al (2017) observed halloysite with a unique morphology in a tephra layer involved in a flow slide and suggested that weak interparticle interactions contributed to the high sensitivity of the material. These findings indicate that evaluation of the surface physicochemical properties of the constituent halloysite mineral and their changes in response to contacting pore water is key to understanding the mechanism of landslide initiation, as well as their runout behavior in volcanic areas.

Methods

Results

Conclusion