9 August 2011
Two new landslide videos – including an amazing pulsing debris flow
Posted by Dave Petley
Another two landslide videos have popped up – and both are fascinating. First, former Durham student Georgie Bennett captured this multi-stage landslide near to Merano in Italy on 2nd August:
Fortunately no-one was killed. Note the weather – fine and sunny – so no obvious trigger.
Second, the Pamir Times has today posted this video of a very large debris flow in Talis village, Ghangche District, in the Baltistan region of northern Pakistan. The Youtube page notes that “At least 60 houses were destroyed by the debris flow disaster that hit Talis village of Ghangche District, in Baltistan region. Last year a similar flood had taken the lives of 13 people at Talis. Around 120 families of Talis have been evacuated to safe areas, where they are living in tents.”
Do watch this one carefully as it captures beautifully the pulses or waves of movement through the mass, with periods of essentially no movement (actually probably creep) between them. The different sizes of the pulse mean that each movement event is different in terms of the amount of material mobilised (sometimes material right up to the banks moves, at other times just the material in the centre of the channel), the velocity and the duration. You will note also that the surface rises as the front of the pulse comes through. Once you get your eye in, this is quite fascinating and surreal to watch.
Comments and thoughts welcome please!
Great videos as always. I have a question about the debris flow — has anyone done a rigorous study combining observation of the flow with looking at the deposit structure after it comes to rest (e.g., by trenching or something)? I’m wondering what, if any, features in the deposit are diagnostic of a pulsing flow like this vs. one that does not. Or, perhaps it’s all too disorganized a fabric to determine. Thanks.
[…] Dave Petley of The Landslide Blog posts two new videos — one of a multi-stage landslide and one of a fascinating muddy debris flow that starts and […]
Landslide related post at Eruptions today:
I observed a similar pulsing flow in the Slano Blato landslide in Slovenia around ten years ago. In the upper mid-section of that landslide, the debris supplied from the breakdown of rotational slumps into the head formed a flow almost entirely (as far as I could see from safe vantage points) comprising sand/silt/clay particles and sufficiently viscous to be able to maintain a stationary sloping surface between pulses. If I remember correctly, each pulse was small compared with the total volume of the flow (e.g. moving only a few cubic metres of material at a time) and short-lived (lasting a few seconds), but occurred several times within the 10-15 minutes that I watched it. I estimated the volume of each pulse at a point further down the landslide in the lower mid-section where the flow was channelled over the edge of a cliff apparently formed a week earlier. In general, the nature of the pulsing flow was similar to that seen in this video. Major stabilisation work has been done at the Slano Blato slide in recent years (visible in Google Earth), so further such activity is unlikely to be seen there.
Great debris flow video!
You commented that there was likely creep. Given the apparent gradation and slope of the flow, wouldn’t there have to be an obvious continual movement across a substantial portion of the flow mass to keep it saturated enough for the next pulse to accelerate the mass as well as drag the peripheral material along. Or does each new pulse create a moving wave of liquefaction that shifts the static mass as the wavefront passes then settles back into stasis as the energy dissipates? It looked like the latter after the initial flow had ceased and that there was no creep.