Davies - adverting predicted


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International Conference Vajont2013 - 8 October

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Davies - adverting predicted

  1. 1. DEALING WITH PREDICTED LANDSLIDE CATASTROPHES Tim Davies Geological Sciences, University of Canterbury, New Zealand
  2. 2. Vajont Predictable (in retrospect…Was the impact predictable?) The event was allowed to happen Would it be any different today?
  3. 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. 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. 5. Waves up to 12 m high at the coast; 5 m at South Bay (Walters et al, 2007).
  6. 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. 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. 8. Slope break Example 2: Franz Josef, NZ Profile line Franz Josef
  9. 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. 10. Cascade rock avalanche ~ 0.7 km3; 500 y BP? Deposit Headscarp Note associated slope break
  11. 11. Round Top rock avalanche 4 x 107 m3: ~ 800 y BP Head scarp Deposit Slope break
  12. 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. 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. 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. 15. Acceptable risk of 400 fatalities ~ 2 x 10-7
  16. 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. 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. 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)