NANOPARTICLES IN THE 2008 YANGJIAGOU ROCK AVALANCHE

Our Yangjiagou rock avalanche fell into a valley called Yangjiagou, from the summit of Weijia Mtn (31° 58’ 01.68” N, 104° 34’ 47.3” E), triggered in the 2008 Wenchuan Earthquake. It buried an earlier rock avalanche probably triggered by a previous large earthquake (Wasowski et al. 2021). It also is a site of ongoing mitigation from repeated debris flows (Li et al. 2021). Since May 2008, the deposit has been deeply eroded in summer monsoon debris flows from floods from a lake dammed by the landslide. The 2008 rock avalanche has a volume of ~3.5 m³ but its contact with the older landslide of unknown age and volume is poorly defined and largely indistinguishable. Both came from a melange of pyrite-rich, black calcareous shale and travelled a similar path. We took 7 samples of sheared vein quartz and shale. To explore the effect of shear strain on grain-size distribution, we experimentally sheared quartz sand, and determined grain-size distributions after a range of different shear strains. Methods are discussed in Hu et al., (2021). We then determined fractal dimensions represented in our size gradings. Fractal dimensions from Yangjiagou suggested that the samples had undergone shear strains of 100–500% during emplacement: a rapidly progresssive brittle rock failure in about 100 s.

Hu W.; Xu, Q.; McSaveney M.; Huang R.; Wang Y.; Chang C.S.; Gou H. & Zheng Y. (2022) The intrinsic mobility of very dense grain flows. Earth and Planetary Science Letters, 580, 117389.

Li, Y., Hu, W., Wasowski J., Zheng, Y-S. & McSaveney, M. (2021) Rapid episodic erosion of a cohesionless landslide dam: Insights from loss to scour of Yangjia Gully check dams and from flume experiments. Engineering Geology 280.

Wasowski, J.; McSaveney, M.J.; Pisano, L.; Del Gaudio, V.; Li, Y. & Hu W. (2021) Recurrent rock avalanches progressively dismantle a mountain ridge in Beichuan County, Sichuan, most recently in the 2008 Wenchuan earthquake. Geomorphology 374.