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Lecture 1 Understanding and forecasting unrest at fast and slow volcanoes

Learn about the differences between fast and slow volcanoes, their magmatic behaviors, triggers, eruptive sequences, precursory activities, magma plumbing, seismic activity, eruption types, and forecasting challenges. Explore case studies like Chaitén, Merapi, Soufrière Hills, Turrialba, and Pinatubo to understand volcanic unrest dynamics.

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Lecture 1 Understanding and forecasting unrest at fast and slow volcanoes

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  1. Lecture 1 Understanding and forecasting unrest at fast and slow volcanoes

  2. Fast volcanoes These commonly re-activate, erupt, and quieten in a short period of time. Their magmas are commonly mobile (hot, crystal-poor, volatile-rich, and bubbly). Examples include Krakatau 1883, Mt. St Helens 1980, and Pinatubo 1991.

  3. Slow volcanoes These systems are restless for years to decades. Their magmas tend to be sluggish (crystal-rich and degassed). Examples include Nevado de Ruiz in Colombia and Popocatépetl in Mexico.

  4. Fast vs slow Both types of systems accelerate and decelerate. But their rates are vastly different, posing particular problems in each case.

  5. Triggers Inputs of deep (mafic) magma Tectonic earthquakes

  6. Chaitén Soufrière Hills Turrialba Merapi Chaitén

  7. Eruptive sequence A series of plinian eruptions in early May 2008, with rapid rise of mobile magma Explosive-effusive activity later in May 2008 Then emplacement of a lava dome until late 2009 or earliest 2010

  8. Chaitén erupting explosively and effusively on 26 May 2008 photo courtesy U.S. Geological Survey

  9. Chaitén lava dome photographed on 24 Jan 2010 Pallister et al. 2013, Andean Geology 40:227-294

  10. Precursory activity at Chaitén Published reports suggest that felt earthquakes began on 30 April, one day before the eruption. However, local accounts may indicate that earthquakes were felt in Chaitén town as early as January 2008. Earthquakes were recorded in 2004-2005.

  11. Lava dome growth as a function of time at Chaitén Pallister et al. 2013, Andean Geology 40:227-294

  12. Magma plumbing beneath Chaitén Michimahuida volcano Liquiñe-Ofqui fault zone Wicks et al., 2011, Nature 478:374-378

  13. Merapi Soufrière Hills Turrialba Merapi Chaitén

  14. Merapi erupting in early November 2010, with before and after images Images courtesy BRGM

  15. Summit deformation in September-October 2010 Surono et al., 2012, J. Volcanol. Geotherm. Res. 241-242:121-135

  16. Types of volcanic earthquakes (long-period earthquake) Courtesy USGS

  17. Seismicity at Merapi, late 2010 Lava dome growing Surono et al., 2012, J. Volcanol. Geotherm. Res. 241-242:121-135

  18. SO2 fluxes lava dome Surono et al., 2012, J. Volcanol. Geotherm. Res. 241-242:121-135

  19. Tectonic triggering of eruptions Volcano station Distant station Surono et al., 2012, J. Volcanol. Geotherm. Res. 241-242:121-135

  20. Soufrière Hills Soufrière Hills Turrialba Merapi Chaitén

  21. 5 km Courtesy NASA

  22. Courtesy NASA

  23. Escalating activity at Soufrière Hills, 1995-1997 Aug-Oct explosions May-June pf activity 18 Sept explosion July-Aug activity Collapse and blast 1996 1997 Sparks et al. 1998, Geophys. Res. Lett. 25:3421-3424

  24. July-August 1996 activity – precursors to the first explosive eruption

  25. 19 August 1997 vulcanian eruption Courtesy The Atlantic

  26. Deformation, seismicity, and vulcanian eruptions, August 1997 C = large dome collapse P = weak explosion E = vulcanian eruption Druitt et al., 2002, Geol. Soc. London Mem. 21:281-306

  27. Turrialba Soufrière Hills Turrialba Merapi Chaitén

  28. Summit region of Turrialba prior to 1996 Courtesy Smithsonian Institution

  29. pH of fumarole condensates, 1992-2009 Martini et al., 2010, J. Volcanol. Geotherm. Res. 198:416-432

  30. SO2 fluxes from Turrialba, 2008-2012 Conde et al., 2014, Int. J. Earth Sci. 103:1983-1998

  31. Carbon/sulfur ratios and SO2 fluxes, 2014-2015 De Moor et al., 2016, J. Geophys. Res. 121:5761-5775

  32. Carbon isotopes of gas at Turrialba, April 2014 Soil gases High-T vents plume atmosphere Malowany et al., 2017, G-cubed

  33. May 2016

  34. In summary…

  35. Fast volcanoes • Long repose periods • High magmatic water contents (~7 wt. %) • Fast magma ascent • Large eruptions • Rapidly decaying activity afterward • Mobile magmas • Are there signs of re-activation well in advance (i.e., years) of eruption ?

  36. Climactic eruption pre-climactic post-climactic ? Chaitén 2008 1 year Merapi 2010 Mt. St. Helens 1980 Mt. Pinatubo 1991 Krakatau 1883 Cordón Caulle 2011 ~2 years El Chichón 1982 0.5 0.1 1 5 Years

  37. Slow volcanoes • Lower magmatic water (~3 wt. % ?) • Slow ramping up • Slow magma ascent • progressive structural opening

  38. Popocatépetl, Mexico, volcanotectonic seismicity, 1990-1994 De la Cruz-Reyna et al., 2008, Bull. Volcanol. 70:753-767

  39. Popocatépetl, Mexico, SO2 fluxes, 1994-1997 First lava dome First eruption Delgado-Granados et al., 2001, J. Volcanol. Geotherm. Res. 108:107-120

  40. FAST SLOW PINATUBO ’91 shallow dacitic reservoir shallow reservoir plexus mid-crustal reservoirs ascent of mafic magma MOHO deep (28-35 km) long-period earthquakes

  41. Some summary thoughts For fast volcanoes, their short precursory period is problematic for forecasting For slow volcanoes, their initiation and termination can be difficult to identify

  42. Seismic forecasting

  43. White and McCausland, 2016, J. Volcanol. Geotherm. Res. 309:139-155

  44. (a) energy FAST large eruption Time (weeks to months) Cumulative VT energy (b) SLOW energy small eruptions Time (years)

  45. Gas forecasting

  46. Mt. St. Helens, 10 April 1980courtesy USGS

  47. Turrialba 2014-2015 De Moor et al., 2016, J. Geophys. Res. 121:5761-5775

  48. (a) FAST energy H2S/SO2 large eruption Time (weeks) Cumulative VT energy (b) CO2/SO2 energy SLOW small eruptions Time (years)

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