Volcano Observatory Best Practice Workshop Near Term Eruption Forecasting

1. Volcano Observatory Best Practice Workshop Near Term Eruption Forecasting Erice, Sicily (IT), 11 - 15 September 2011 CALDERAS Problems and challenges for near-term eruption forecasting Paolo Papale INGV, Italy

2. CALDERAS: some general facts • Caldera-forming eruptions are the largest eruptions on Earth. For example, the Fish Canyon eruption in southwestern Colorado (United States) about 28 million years ago erupted more than 5,000 km3 of magma from La Garita caldera. That's enough magma to bury the entire state of California to a depth of nearly 12 m! • At least 1,299 episodes of unrest have occurred at 138 calderas greater than 5 km in diameter during historical time. • In a typical year some form of unrest (earthquakes, ground deformation, change in fumarole activity, or eruptions) occurs at about 18 large calderas worldwide, and eruptions occur within or near at least five of them. source: http://volcanoes.usgs.gov/images/pglossary/caldera.php

3. CALDERAS: why are they different? • The structure of calderas is profoundly different from that of stratovolcanoes • “negative” as opposed to “positive” edifice • boarder faults • chaotic rock assemblage • development of large geothermal circulation • resurgency • compressional/extensional portions • several distinct post-collapse vents • …

4. post-collapse eruptive vents main caldera border extensional setting internal caldera resurgent block extensive degassing CAMPI FLEGREI, Southern Italy maximum uplift area compressional setting

5. CALDERAS: why are they different? They often display unrest dynamics that if observed at central volcanoes, they would almost certainly culminate into an eruption • Observations that are often reported as “critical” for near-term eruption forecast: • acceleration in seismicity • acceleration in deformation • increase of gas fluxes, especially CO2 flux (and concentration) • (re: first two days of VOBP workshop) Are they equally diagnostic / critical at calderas?

6. CAMPI FLEGREI Vertical displacement during last 2 centuries > 8,000 earthquakes recorded  3.5 m of ground uplift In 1983 about 40,000 people were evacuated from the town of Pozzuoli, officially, due to the risk of structural collapses as a consequence of rapid ground displacement and seismic swarms

7. Campi Flegrei, Italy, 1980-2008 From: Chiodini et al., 2008.

8. RABAUL eruption, 1994 “The eruption began on September 18 after less than a day of intense seismicity…” “The people who lived there were reminded of the inevitability of an eruption by intense earthquake activity and uplift of the ground within the caldera in the mid-1980's.” “However, despite warnings and a declared stage-2 emergency in 1983 and 1984, Rabaul did not erupt and, in fact, activity waned and remained at low levels until hours before the latest eruption broke out…” Source: http://hvo.wr.usgs.gov/volcanowatch/1994/94_09_23.html

9. CALDERAS: why are they different? Vent location is definitely more uncertain than for central volcanoes map of the probability of venting for a next eruption at Campi Flegrei from Selva et al., 2011 5 km

10. RABAUL, 1994: several vents up to km apart were active “At times on September 19, there may have been as many as five active vents along the caldera rim, including several that began below the sea...” Source: http://hvo.wr.usgs.gov/volcanowatch/1994/94_09_23.html

11. CALDERAS: why are they different? Many caldera depressions are partially or totally filled with water Geothermal circulation is usually well developed below caldera floor Phreatic explosions and phreatomagmatic eruptions can be frequent at calderas

12. During last 3 decades a number of interpretations have been proposed for the 1982-84 crisis at Campi Flegrei. Based on signal inversion and forward modeling, ground displacement has been alternately interpreted as mainly due to: • increased heat/fluid flow in the geothermal system • emplacement of a shallow magma body CALDERAS: some “hot” questions • what’s the origin of unrest at calderas, and why so often large unrest dynamics do not culminate into an eruption?

13. Inversion of P-wave velocity and gravity at Campi Flegrei High velocity – High Density 3D integrated vP model of Campi Flegrei Seismic attentuation tomography From De Siena et al., 2010 From A. Zollo and co-workers

14. 200-500 m 200-500 m  0.1 km3

15. 0,9 0,9 0,8 0,8 0,7 0,7 0,6 0,6 0,5 0,5 volume (DRE) volume (DRE) 0,4 0,4 0.25 km3 0,3 0,3 0,2 0,2 0.1 km3 0,1 0,1 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 eruzione eruzione AD 1538 Monte Nuovo Magnitude of last 5 ka activity at Campi Flegrei volume (km3 DRE) volume (DRE) eruzione eruzione From Di Vito and Orsi, 2009

16. Top of carbonatic basement top of carbonatic basement Top of carbonatic basement Seismic discontinuity pressure (MPa) depth (km) Seismic discontinuity Vesuvius composition of the gas phase (wt% CO2) Campi Flegrei pressure (MPa) depth (km) composition of the gas phase (wt% CO2)

17. CO2~ 60 - 80 wt% in the gas phase 1.5 – 3 km depth Plinian phase D1 of the 4100 BP Agnano Monte Spina eruption From Rutherford, this project and previous GNV Campi Flegrei Project

18. Agnano Monte Spina eruption shallow phonolite A few tens of hours before discharge deep trachyte From Rutherford, INGV-DPC Projects 2001-03/17 and 2004-06/V3_2

19. AVERNO Eruption IC Eruption AMS Eruption AMS Eruption Chemical and isotopic evidence of mixing-mingling preceeding many CF eruptions From: Civetta, 2009

20. Schematic view of Campi Flegrei system in the past 5 ka. large geothermal circulation heterogeneous, mostly shoshonitic, CO2-rich, large (>100 km3) magma reservoir

21. CALDERAS: some “hot” questions • what’s the origin of unrest at calderas, and why so often large unrest dynamics do not culminate into an eruption? • how to discriminate between unrest leading or not leading to an eruption? (e.g., dominantly due to the action of magma vs. dominantly due to the action of geothermal fluids) • how to relate observations to expected vent location? • how to deal with often decades-long unrest dynamics? • how long in advance will the signals allow robust forecast? • how to evaluate the hazard (and risk) related to often intense unrest dynamics?

22. Schematic view of Campi Flegrei system in the past 5 ka. large geothermal circulation what controls the size of an eruption at calderas? or, do we need large magma bodies at shallow depth for a new caldera-forming eruption? heterogeneous, mostly shoshonitic, CO2-rich, large (>100 km3) magma reservoir

23. More general interpretation issue: Whether unrest at calderas (e.g., Long Valley, Yellowstone, Campi Flegrei, …) simply punctuates long periods of quiet or is the early warning sign of future eruptions is an important but still unanswered question

24. Short-term volcanic hazard forecast at calderas is generally characterized by uncertainties larger than for central volcanoes!

25. Campi Flegrei – Pre-eruptive Event Tree DELPHI METHOD Boolean parameters are represented by “YES” “Gray areas” correspond to variable probability of being in the adjacent states, depending on the measured values Red parameters: Seismicity Green parameters: Deformation Blue parameters: Geochemistry after Selva et al., 2011

26. 1 unrest 0.9 0.8 0.7 0.6 0.5 0.4 magmatic 0.3 0.2 eruption 0.1 0 1981 1982 1983 1984 1985 Application to Campi Flegrei crisis 1982-1984 Probability estimates: beyond the color codes after Selva et al., 2010

27. Colour code Continuous probabilities (with uncertainties) Green: normal Yellow: watch Orange: attention Red: crisis Correctly communicate the uncertain nature of predictions Artificial discretization forces actions to be strictly tied to evaluation from scientists Allow a clear distinction of roles and responsibilities between scientists and decision-makers Scientists become de-facto decision-makers

28. after Voight et al., 2006 vertical displacement (m) ULP ground oscillations 0 2 4 6 time (hours) GLOBAL VOLCANO MODEL(S) after Longo et al., 2010