Managing ash fall impacts from large silicic eruptions: Lessons from Patagonia

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Managing ash fall impacts from large silicic
eruptions Lessons from Patagonia

• Tom Wilson1 Carol Stewart1 Graham Leonard2
  Gustavo Villarosa3 Valeria Outes3 Heather
  Bickerton1 Peter Baxter4 Eli Rovere5
• 1University of Canterbury, New Zealand
• 2 GNS Science, New Zealand
• 3 Universidad de Comahue, Argentina
• 4University of Cambridge, United Kingdom
• 5 SEGEMAR, Argentina

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Context Ash Impacts

• Volcanic ash is the most likely volcanic hazard
  to affect the most people during an explosive
  eruption
• Typically disruptive, rather than destructive
• Although can potentially create a variety of
  unique impacts
• Due to the wide range of potential ash sources
  and characteristics it becomes complicated
  estimating what impacts will be
• Thickness, grainsize, leachate, etc.

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Recon Trips by volcano year visited
Eldfell (Heimaey) 2008
Redoubt 1996 2010
Shinmoedake 2011
Etna 2003
Sakurajima 2001
Pacaya 2010
Pinatubo 2007
Merapi 2006
Tungurahua 2005 2010
Lapevi 2003-05
Ruapehu 1995-96
Hudson 2008
Chaiten 2009
Puyehue Cordon-Caulle 2012
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What pops up time after time...

• Volcanic ash falls are often regarded as exotic
  events (mysterious) which are rarely planned for

• Health (most important!)
• What does ash do to me.to my children?
• What will ash do to water supplies?
• What impact will it have on food?
• Farming
• What will ash do to my animals?
• What will ash do to my crops?
• How can I remediate the damage?
• How much Fluoride is in the ash?
• Infrastructure
• Unexpected. Exotic
• Wow this ash stuff was hard to clean up.
• More time than expected
• Didnt expect those impacts. Can we mitigate?
• Wish we had planned for this

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Outputs from this research?

• Emphasis on preparedness and mitigation
  strategies
• Strong focus on end user needs
• Attempts to be considered, accurate, practical
• http//vatlab.org

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Can we begin to forecast impact thresholds for
urban areas?What does heavy ash fall actually
mean?

• New Zealand and Patagonia share similar
• Latitude
• Volcanoes
• Climate (esp. west)

PUYEHUE CORDON-CAULLE
CHAITEN
HUDSON
7
Jaccobacci
40S
PCC
Villa La Angostura

• 2011 Puyehue Cordon-Caulle Eruption
• VEI 4
• 4.5 km3 bulk volume
• 150,000km2 affected
• Rhyodacite

Bariloche
CHAITEN
Chaiten
Esquel
Futaleyufu

• 2008 Chaiten Eruption
• VEI 4
• 0.5-1.0 km3 bulk volume
• 150,000km2 affected
• Rhyolite

Trevelin
HUDSON
Puerto Ibanez

• 1991 Hudson Eruption
• VEI 5
• 4.3 km3 bulk volume
• 100,000km2 affected
• Trachyandesite-rhyodacite

Chile Chico
Los Antiguos

• References
• PCC Villarosa et al. unpub data
• Chaiten Watt et al. 2009 Alfano et al. 2011
• Hudson Scasso et al. 1994

Perito Moreno
Tres Cerros
50S
Puerto San Julian
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• 2008 Chaiten eruption, Chile
• 75 mm of ash fall induced infrastructure failure
  in Futaleufu, Chile (2,000 residents - temporary
  evacuation)
• Water supply compromised
• Power supply cut
• Roads disrupted by thick ashfalls
• Health concerns
• Compounded effects
• Evacuation duration 1-12 months

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Eruption Eruption HUDSON 1991 HUDSON 1991 HUDSON 1991 HUDSON 1991 HUDSON 1991 HUDSON 1991 CHAITEN 2008 CHAITEN 2008 CHAITEN 2008 CHAITEN 2008 PUYEHUE CORDON-CAULLE 2011 PUYEHUE CORDON-CAULLE 2011 PUYEHUE CORDON-CAULLE 2011
Town Affected Town Affected Puerto Ibanez Chile Chico Los Antiguos Perito Moreno Tres Cerros Puerto San Julian Chaiten Futaleyufu Trevelin Esquel Villa La Angostura Bariloche Jaccobacci
Distance from Vent (km) Distance from Vent (km) 90 120 125 175 473 545 11 75 100 110 44 90 231
Ash hazard character- istics Thickness of ash fall (mm) 20 100 80 20 40 5 20 30 15 10 150 40 35
Ash hazard character- istics Duration of main ash fall 4 days 4 days 4 days 4 days 2-4 days 2-4 days 3 days 6 days 4 days 2-3 days 5-6 days 5-6 days 5-6 days
Ash hazard character- istics Remob of ash (duration) 15 years 15 years 15 years 15 years 5-10 years 5-10 years 0.5-4 years 1-2 years 6-18 months 6-18 months 6-12 months 6-12 months gt18 months
Critical Infra-structure Power
Critical Infra-structure Water
Critical Infra-structure Ground Transport
Critical Infra-structure Waste-water Sewage
Critical Infra-structure Telecom
Municipal Cleanup Undertaken Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes
Municipal Cleanup Duration
Evacuation of population Official Evac Yes No No No No No Yes Yes No No No No No
Evacuation of population Self evac immediate lt50 lt50 lt30 lt25 gt75 lt5 100 gt50 lt5 lt5 lt20 lt5 lt20
Evacuation of population Self evac - long term lt50 Yes Yes Yes gt75 Yes gt50 -- -- -- ??? -- --
Ground transportation most common and often
longest disruption. Roads (and properties)
require clean up ? costly and time consuming
Electrical Water high dependence ? high
disruptive impact System design key factor
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General findings for infrastructure

• Disruptive rather than catastrophically damaging
• Most infrastructure systems will tolerate
  volcanic ash...up to a point
• Loose relationship with ash thickness/load, but
  strongly influenced by
• system design
• level of planning
• adaptive capacity
• The complex characteristics of volcanic ash can
  create a range of possible direct and indirect
  impacts
• Possibly leading to complex, cascading effects
• Individual case-by-case assessment approach
  probably most appropriate

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Evacuations

• Official evacuations rare
• But self-evacuation very common
• Persistence of ashy conditions (direct or reomob)
  will influence duration of evacuation
• Few evacuation from fear of roof collapse
• insufficient ash loads

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Summary 1 Thresholds

• Evidence supports the view of cities as complex
  self organising systems
• (e.g. Alesch Siembieda 2012)
• Hypothesis of establishing a critical threshold
  of ash hazard intensity for common levels of
  disruption across city is probably null
• But we can use it as a guide

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Summary 2 Thresholds?
Ash Thickness Urban Infrastructure Systems Evacuation considerations
1 mm Mostly nuisance Public health concerns
10 mm Some limited impacts to infra. systems. Depends on system design Some self evacuation.
75 mm Widespread disruption to infra. systems. Self evacuations likely, may extend up to months depending on ashy conditions residual functionality
400 mm Not observed but likely to result in widespread disruption and damage to systems Livelihoods compromised ? long term evacuation likely.

• Remobilisation of ash (esp. on regional scale) is
  just as disruptive as primary fall as it extends
  duration of impact
• Infrastructure networks (electricity, road,
  water)
• Agriculture (highly sensitive)

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Thank you. Any questions?

• Going forward from here
• Need detailed understanding of what will be the
  likely impacts at varying levels of hazard
  intensity
• Heading to the lab...
• Wardman (talk and poster this session)
• Current recon trip methodology doesnt allow
  for in-depth analysis.
• Developing local capacity key

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Context Ash Impacts

• Recent experience in New Zealand and beyond
  indicates volcanic risk scientists need to give
• Timely and often highly specialized impact and
  mitigation information to stake-holders and
  end-users
• Non-crisis period
• Integrated, on-going and dynamic risk reduction
  and readiness strategies with all stakeholders
  are optimal
• Yet, there is regular change of personnel,
  organizations and arrangementsetc
• Crisis period
• Scientists often scrambling into the field to
  collect data.
• Reduces (or negates) their ability to share
  information in a timely manner
• Diversity of potential impacts makes it hard to
  make robust, meaningful estimates to
  stake-holders

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