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Davies - adverting predicted

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International Conference Vajont2013 - 8 October

International Conference Vajont2013 - 8 October

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  • 1. DEALING WITH PREDICTED LANDSLIDE CATASTROPHES Tim Davies Geological Sciences, University of Canterbury, New Zealand
  • 2. Vajont Predictable (in retrospect…Was the impact predictable?) The event was allowed to happen Would it be any different today?
  • 3. 1963-2013: What has changed? 1. The Vajont catastrophe occurred and is fairly well understood 2. Landslide physics has made some progress 3. Landslide and flood modelling are much more advanced – consequences can be estimated if location and volume can be predicted What has not changed? 1. Politics is a very important factor in risk management decision-making 2. Risk is a poorly-understood topic; acceptable risk is poorly defined 3. Communication between scientists and non-scientists is poor 4. Decision-makers are reluctant to acknowledge inevitable future catastrophes
  • 4. Example 1: Kaikoura, New Zealand State highway & rail South Bay Kaikoura Goose Bay Sediment accumulation 0.25 km3 Kaikoura Canyon Assuming the whole 0.25 km3 of sediment can fail at once, the resulting tsunami has been modelled
  • 5. Waves up to 12 m high at the coast; 5 m at South Bay (Walters et al, 2007).
  • 6. This has been known about since 1999 Consequences: coseismic failure means NO WARNING - hundreds of deaths, up to $1Bn costs The reality of the complete collapse scenario has not been investigated until now – lack of funding RISK (probability * consequence): Estimated recurrence interval of this event ~ 200 years (Lewis & Barnes 1999) Number of deaths ~ 100; giving 0.5 deaths per year
  • 7. Acceptable risk of numbers of potential fatalities from dam failure (Munger et al., 2009) Dam failure: known hazard, known location, known consequences; Applicable to known future landslide failure Acceptable risk of 100 fatalities ~ 10-6 per year Risk at Kaikoura is unacceptable by 5 orders of magnitude
  • 8. Slope break Example 2: Franz Josef, NZ Profile line Franz Josef
  • 9. 1 km ? Township Slope profile Alpine fault Alpine fault generates M8 earthquakes every ~ 300 years; last rupture was in 1717. Is this a deep-seated coseismic/gravitational slope deformation? Is there a failure surface that extends with every earthquake? Could this slope fail as a coseismic rock avalanche (> 107 m3)?
  • 10. Cascade rock avalanche ~ 0.7 km3; 500 y BP? Deposit Headscarp Note associated slope break
  • 11. Round Top rock avalanche 4 x 107 m3: ~ 800 y BP Head scarp Deposit Slope break
  • 12. The Franz Josef slope has been through ~ 50 earthquakes since deglaciation without collapsing, so the probability it will fail in the next earthquake is say 1% The annual probability of an earthquake is about 1%, so the annual probability of a rock avalanche is about 10-4 The number of people who will be killed is at least 100; so the average annual death rate is ~ 10-2; unacceptable by a factor of about ten thousand Acceptable risk of 100 deaths ~ 10-6 per year
  • 13. Example 3: Milford Sound, NZ Iconic World Heritage tourist location > 600,000 day visitors per year All within 5 m of sea level
  • 14. There are > 20 postglacial landslide deposits > 106 m3 on the bottom of the Sound About every 1000 years there is a coseismic landslide that causes a tsunami with about 10 m of runup; on average this will kill about 400 people at current visitor rates (Dykstra, 2013) The risk to an individual tourist is < 10-6 per lifetime – this is acceptable The risk to each live-in employee is about 10-3 per year – much higher than acceptable under employment safety legislation The societal risk is about 0.4 per year - ~ a million times greater than acceptable
  • 15. Acceptable risk of 400 fatalities ~ 2 x 10-7
  • 16. It is extremely difficult to persuade authorities to investigate such situations. DO WE NEED: • MORE & BETTER SCIENCE? YES – BUT THAT’S NOT THE PROBLEM • BETTER SCIENCE COMMUNICATION? YES – BUT HOW TO DO IT? Obstacles to communication 1. Time-scales. Decision-makers – maybe 10 years Geologists - > millennia 2. Risk tolerance. Decision-makers – unusually high Scientists & public - lower 3. Politicians don’t understand geology; Geologists don’t understand politics BUT – POLITICIANS CAN BE HELD ACCOUNTABLE If comprehensible published science is ignored by politicians, they will be held responsible for the resulting disaster when it happens...
  • 17. How does this apply to Milford Sound, Franz Josef, Kaikoura? Reduction of the societal risk to acceptable levels at Milford Sound is only possible by reducing visitor numbers by a factor of about 1 million – i.e. abandoning the site as a visitor destination This will be politically and economically unacceptable; there is a serious problem A possible solution would be for the society running the risk – NZ society – to knowingly and willingly accept the risk and its consequences. A necessary first step is for the risk information to be peer-reviewed and published so that it is publically available. Then an informed society-wide (public/government) debate can take place… The key responsibility of the scientist is to communicate the information on risk and consequence to the public and decision-makers – in such a way that is is accepted and understood. Then it might be acted on…
  • 18. tim.davies@canterbury.ac.nz It is also crucial for scientists to publically correct any public misinterpretation of science by politicians and others (including scientists)