22 September 2015

The 1991 Touzhai rock avalanche in China

Posted by Dave Petley

The Touzhai rock avalanche

On 23rd September 1991, at 18:10 local time, the catastrophic Touzhai rock avalanche occurred  Zhaotong, Yunnan Province in SW China. This was a large event – the estimated volume of the Touzhai rock avalanche is 15 million cubic metres, and the landslide had a runout distance of over 3.5 km.  After descending a vertical distance of about 950 m the landslide destroyed 202 houses in the village of Touzhai, killing 216 people.  In a paper in the journal Landslides, Xing et al. (2015) (and with a stellar list of authors) have provided a detailed description of this landslide, and have modeled its movement using DAN-W software..

The landslide occurred after a prolonged period of heavy rainfall.  Failure occurred on a steep slope in basalt over an area that was 900 m long (in terms of the slide direction) and up to 700 m, with a thickness of between 5 and 120 m. This is the headscarp are as shown in the paper:-


The headscarp of the Touzhai rock avalanche, from Xin et al. 2015

The headscarp of the Touzhai rock avalanche, from Xing et al. 2015


The structural control of pre-existing joints is quite clear.  This looks to be a rather complex wedge type failure.  This mass fragmented and transitioned into a rapid flow that travelled down the valley to hit the village below.  The modelling of the landslide suggests that it had a peak velocity of just under 50 m/sec and an average velocity of 21 m/sec, giving a duration of the Touzhai rock avalanche of 175 seconds from the initial rupture event.  This is the image of the landslide itself from the paper:

Touzhai rock avalanche

The headscarp of the Touzhai rock avalanche, from Xing et al. 2015


This landslide highlights one of the major issues managing the hazard associated with rock avalanches.  The flow initiated in hard rock, but not on a near vertical cliff, over 3 km from the village.  Identifying those areas that might be susceptible to such a failure is really difficult, and forecasting the likely runout speed and distance of the flow is also an enormous challenge.  We still have a lot of work to do in this area, but detailed studies such as this are a great help.


Xing, A, Wang, G., Yin, Y. Tang, C., Xu, Z., and Li, W. 2015. Investigation and dynamic analysis of a catastrophic rock avalanche on September 23, 1991, Zhaotong, China. Landslides, 13 pages. Published online 11th August 2015.