Tara Shreve1,2*, Raphael Grandin2, and Marie Boichu3 1Carnegie Insqtuqon for Science, Earth and Planets Laboratory, Washington

Home , Copahue

Can high rates of passive volcanic gas emissions induce reservoir depressurizaton at Ambrym volcano (Vanuatu)? Landsat-8 Tara Shreve 1,2*, Raphael Grandin2, and Marie Boichu3 1Carnegie Insttuton for Science, Earth and Planets Laboratory, Washington, DC (USA) 2Insttut de Physique du Globe de Paris, Université de Paris (France) 3Laboratoire d’Optque Atmosphérique, Université de Lille (France) *[email protected] vEGU 2021 1 1. Context ‣ Volcanic gas emissions 2. Case study

‣ Ambrym 2018 erupton: Silencing the world’s top passive SO2 gas emiter 3. 2015–2017 subsidence episode 4. Geodetc modelling 5. Theoretcal modelling ‣ Couple gas emissions to reservoir depressurizaton 6. Conclusions and perspectves ‣ Can mass loss by gas emissions promote reservoir depressurizaton, magma replenishment and erupton? Outline vEGU 2021 2 100 Carn et al., 2017 ‣ SO2 fuxes at volcanoes can exceed 1 kt day-1 and total gas fuxes are an 1. Ambrym 36. Chikurachki 71. Ketoi 2. Kilauea 37. Mayon 72. Chiginagak 3. Bagana 38. Asama 73. Tokachi order of magnitude larger 4. Nyiragongo-Nyamuragira 39. Gaua 74. Piton de la Fournaise 5. Aoba 40. Sirung 75. Spurr 6. Etna 41. Redoubt 76. Jebel-at-Tair 7. Tavurvur 42. Shishaldin 77. Santa Ana 8. Dukono 43. Tungurahua 78. San Miguel 9. Popocatepetl 44. Copahue 79. Sabancaya ‣ Efect of gas emissions on reservoir 10. Manam 45. Sinabung 80. Ebulobo 11. Yasur 46. Karangetang 81. Isluga 12. Anatahan 47. Krakatau 82. Rinjani pressurizaton is not well studied 13. Soufriere Hills 48. Kerinci 83. Augustine 14. Nevado del Ruiz 49. Tofua 84. Sangeang Api 10 15. Sakura-jima 50. Villarrica 85. Kanlaon 16. Miyake-jima 51. Michael 86. Dalafilla-Erta Ale 17. Karymsky 52. Sarychev 87. Paluweh 18. Masaya 53. Tinakula 88. Erebus ‣ Ambrym (Vanuatu) strongest passive 19. Suwanose-jima 54. Veniaminof 89. Gareloi 20. Bromo-Semeru 55. White Island 90. Marapi

Cumulative number 21. Mutnovsky-Gorely 56. Fuego 91. Merapi 22. Turrialba 57. Lastarria volcanic emiter of SO2 from 2005– 23. Kizimen 58. Santa Maria 24. Avachinsky 59. Barren Island 25. Batu Tara-Lewotolo 60. Ubinas CO /SO ratio: -1 26. Raung-Ijen 61. Galeras 2 2 2015 (7 kt day ) (Carn et al., 2017) 27. Ulawun 62. Reventador 28. Langila 63. Bulusan Measured (n = 40) 29. Aso 64. Slamet 30. Nevado del Huila 65. Lokon-Empung Not measured (n = 51) 31. San Cristobal 66. Korovin 32. Satsuma-Iojima 67. Kudriavy ‣ Inter-eruptve subsidence episode at 33. Pagan 68. Stromboli 34. Kliuchevskoi 69. Cleveland 35. Shiveluch 70. Montagu Ambrym from 2015–2017 1 10 100 1000 10000 Mean SO2 flux (tons/day) ‣ Physical mechanism unexplained Physics-based models can help discriminate between processes driving subsidence.

Context vEGU 2021 3 ‣ Rif zone intrusion and submarine 167˚ 169˚ 100 km erupton in 2018 (Shreve et al., c. PAC 2019, Moussallam et al., 2021) AUS ‣ Intruded volume >0.4 km3 Aoba

‣ <5 cm pre-eruptve uplif 16˚ − 15˚ Ambrym

−2 −1 01234 15 pt Opening (m)

− 17˚ PAC

4.5 km AUS 9 Volcanoes Rift zones Shreve et al., 2019

Case study vEGU 2021 4 ‣ Rif zone intrusion and submarine erupton in 2018 (Shreve et al., 2019, Moussallam et al., 2021) ‣ Intruded volume >0.4 km3 Can mass loss by sustained ‣ <5 cm pre-eruptve uplif passive gas emissions promote reservoir −2 −1 01234 Opening (m) depressurizaton, magma replenishment and erupton?

4.5 km

Shreve et al., 2019

Case study vEGU 2021 5 ‣ Sentnel-1 tme series calculated using MintPy (Yunjun et al., 2019) estmates max subsidence rate of ~10 cm year-1 from Oct. 2015—Oct. 2017

‣ No evidence of eruptve actvity aside from lava lakes

‣ Subsidence ends abruptly around October 2017 afer seismicity increase (Global Volcanism Program, 2017)

Sentnel-1 velocity map, 2015–2017 t on increase Seismicity Seismicity

Reference 2018 erup LOS displacement (m) displacement LOS Sentnel-1 ascending tme series ALOS-2 ascending interferogram

Subsidence vEGU 2021 6 Episode E = 5 GPa ‣ Joint inversion of Sentnel-1 tme series ν = 0.25 average velocity map (Oct. 2015—Oct. 2017) and scaled ALOS-2 interferogram (March 2015—Oct. 2017) using DefVolc, a Mixed Boundary Element Model and 2 km neighborhood algorithm (Cayol et al.)

‣ Assume horizontal ellipsoidal reservoir

‣ Geodetc inversion estmates a thin, elongated and shallow source ~2 km b.s.l. Opening (m) Best-ft model ΔV = -3 x 106 m3 year-1 ΔP = -2.15 MPa year-1

Geodetc vEGU 2021 7 Modelling data synthetics residuals

nel-1 velocity map velocity t nel-1 Sen ( 30 Oct 2015–31 Oct 2017) 2015–31 Oct 30 Oct (

LOS displacement (cm/year) ( 21 Mar 2015–28 Oct 2017) 2015–28 Oct 21 Mar ( scaled interferogram, ALOS-2 Geodetc vEGU 2021 8 Modelling 10-4 Best-ft model 2 Marginal Probability ‣ EstmateMax. PPD Modelmean model and Mean Model 1 Density Functons uncertaintes by Cent. E (km) E Cent. 0 Mean model 106 8.202 Marginal Probability Density Functions approximatng posterior Max. PPD Model 8.2 95% confdence intervals Mean Model 8.198 probability density Cent. N (km) N Cent. functon using 10,000 0 -2000 resampled points -4000 Depth (m) Depth (Sambridge, 1998) 6000

4000 S1 (m) S1 2000 Mean model 10

5 -1

S1 over S2 over S1 ΔP = -3.6 ± 1.6 MPa year

5 S2 over S3 over S2

180 160 140 120

Strike (°) Strike 100 80

0 -2 -4 (MPa) -6 Pres. Change Change Pres. 1.9 1.92 1.94 1.96 8.198 8.2 8.202 -4000 -2000 0 2000 4000 6000 4 6 8 10 2 4 6 8 10 80 100120140160180 -6 -4 -2 0 105 106 Pres. Change Cent. E (km) Cent. N (km) Depth (m) S1 (m) S1 over S2 S2 over S3 Strike (°) (MPa) Geodetc vEGU 2021 9 Modelling 10-4 2 Max. PPD Model Mean Model 1

0 106 8.202 Marginal Probability Density Functions Max. PPD Model 8.2 Mean Model 8.198

-2000

-4000

6000

4000

2000

180 160 140 120 100 Best-ft model

80 Pressure change rates estmated Mean model

from geodetc models: 95% confdence intervals 0 ‣ Best-ft model: -2.15 MPa year-1 -2 ‣ Mean model: -3.6 MPa year-1 -4 ‣ Upper bound (+ 1 standard -6 deviaton): -2 MPa year-1 1.9 1.92 1.94 1.96 8.198 8.2 8.202 -4000 -2000 0 2000 4000 6000 4 6 8 10 2 4 6 8 10 ‣ Lower80 100120140160180bound (- 1 standard -6 -4 -2 0 -1 105 106 deviaton): -5.2 MPa year Pres. Change (MPa)

Geodetc vEGU 2021 10 Modelling Adapted from Girona et al, 2014

Q ‣ Lumped parameter theoretcal model from Girona et al., 2014 Gas Plume

Adapted from ‣ Mass loss from conduit due to Girona et al., 2014 k gas emissions is balanced by a μ Conduit pressure decrease in the L hydraulically-connected reservoir β c Shallow R Reservoir V , α c r [mg,c(t) + mm,c(t)]g D nr P(t) k r ΔP(t) = P(t) − P(t ) = − P(t ) 0 πR(t)2 0

? M

Rd Deeper magma source

Theoretcal vEGU 2021 11 Modelling Adapted from Girona et al, 2014

Q ‣ Lumped parameter theoretcal model from Girona et al., 2014 Gas Plume

Adapted from ‣ Mass loss from conduit due to Girona et al., 2014 k gas emissions is balanced by a μ Conduit pressure decrease in the L Pressure hydraulically-connected reservoir β c Shallow change R Reservoir V , α c r [mg,c(t) + mm,c(t)]g D nr P(t) k r ΔP(t) = P(t) − P(t ) = − P(t ) 0 πR(t)2 0

? M Mass of gas Mass of in conduit (incompressible) Rd Deeper magma source Conduit radius melt in conduit

Theoretcal vEGU 2021 12 Modelling Assumptons include: Adapted from Girona et al, 2014

Constant H2O Open conduit degassing rate Undegassed parent melt Gas Plume Melt volume in conduit Denser degassed melt decreases when gas emited k μ Conduit L Gas separaton Maxwell β c Shallow viscoelastc Reservoir Rc Vr, α rheology D n Crystal content neglected r P(t) kr Constant temp.

Adapted from ? M Pressure-dependent gas Girona et al., solubility 2014 Incompressible melt Rd Deeper magma source Theoretcal vEGU 2021 13 Modelling Fixed parameters: Adapted from Girona et al, 2014

Gas Plume Mean H2O degassing rate 90 kt day-1 from Carn et al., 2017, k Allard et al., 2015 μ Reservoir depth Conduit L 2 km b.s.l. from geodetc β c Shallow inversion Reservoir Reservoir geometry Rc Vr, α D n Sill-like r P(t) kr from geodetc Dissolved volatles inversion 1.3 wt% H2O Adapted from ? M from Allard et al., Girona et al., 2015 2014

Rd Deeper magma source Theoretcal vEGU 2021 14 Modelling Weak Constraints: Adapted from Girona et al, 2014

Gas Plume Degassed and undegassed melt

k density μ Conduit Conduit L Reservoir β radius c Shallow volume Reservoir Rc Vr, α D n r P(t) kr

Adapted from ? M Girona et al., 2014

Rd Deeper magma source Theoretcal vEGU 2021 15 Modelling Case 0: ‣ Elastc half-space d ρm̂ ,c(t) ‣ Steady-state magma convecton ( = 0) dt ‣ Gas exsolves in conduit

‣ Reservoir volume (Vr) ≫ volume of melt in conduit (Vm,c)

Theoretcal vEGU 2021 16 Modelling Adapted from Girona et al, 2014 Case 0: Q ‣ Elastc half-space d ρm̂ ,c(t) ‣ Steady-state magma convecton ( = 0) Gas Plume dt ‣ Gas exsolves in conduit Adapted from Girona et al., ‣ Reservoir volume (Vr) ≫ volume of melt in conduit (Vm,c) 2014 k μ Conduit L β c Shallow Reservoir Rc Vr, α D nr P(t) k r ̂ gρm̂ ,c(t0)kQt ΔP(t) = − 2 ? M πRc(t0) ρwk + gρwρm̂ ,c(t0)Vr(t0)

Rd Deeper magma source

Theoretcal vEGU 2021 17 Modelling Adapted from Girona et al, 2014 Case 0: Q ‣ Elastc half-space d ρm̂ ,c(t) ‣ Steady-state magma convecton ( = 0) Gas Plume dt ‣ Gas exsolves in conduit Adapted from Girona et al., ‣ Reservoir volume (Vr) ≫ volume of melt in conduit (Vm,c) 2014 k Mean density μ Mean H O Conduit of melt in 2 L degassing conduit β rate c Shallow Reservoir Rc Vr, α D nr P(t) k r ̂̂ gρm̂̂ ,c(t0)kQt ΔP(t) = − 2 ? M πRc(t0) ρwkk + gρwρm̂̂ ,c(t0)Vr(t0) Partal density R d Deeper magma source of water in Reservoir Host rock bulk melt volume modulus Theoretcal vEGU 2021 18 Modelling Host rock bulk modulus, k = 500 MPa accountng for a compressible Given a fxed undegassed sill-like reservoir kg m−3 ρnd = 2430 and degassed melt density, Undegassed parent melt density ρ = 2670 kg m−3 a wide range of reservoir c1 Degassed melt density and conduit parameters produce depressurizaton rates that are within uncertaintes estmated with geodetc models.

Results vEGU 2021 19 Host rock bulk modulus, k = 500 MPa accountng for a compressible Given a fxed undegassed sill-like reservoir kg m−3 ρnd = 2430 and degassed melt density, Undegassed parent melt density ρ = 2670 kg m−3 a wide range of reservoir c1 Degassed melt density and conduit parameters produce depressurizaton rates that are within uncertaintes estmated with geodetc models. How does undegassed and degassed melt density afect depressurizaton rates for realistc range of conduit radii (10–150 m)? Results vEGU 2021 20 Host rock bulk modulus, k = 500 MPa accountng for a compressible Given a fxed undegassed sill-like reservoir kg m−3 ρnd = 2430 and degassed melt density, Undegassed parent melt density ρ = 2670 kg m−3 a wide range of reservoir c1 Degassed melt density and conduit parameters produce depressurizaton rates that are within uncertaintes estmated with geodetc models. How does undegassed and degassed melt density Realistc range of conduit afect depressurizaton radii: 10–150 m rates for realistc range of conduit radii (10–150 m)? Results vEGU 2021 21 km3 Reservoir volume Vr = 10 m Rc = 10 Conduit radius For small conduit radius (~10 m) and small reservoir volume (~10 km3), lower rates of depressurizaton are estmated when there is a small density diference (<70 kg m-3) between degassed melt and undegassed parent melt.

Results vEGU 2021 22 Case 1: ‣ Viscoelastc half-space (μ = 1018 Pa ⋅ s) d ρm̂ ,c(t) ‣ Steady-state magma convecton ( = 0) dt ‣ Gas exsolves in conduit

Theoretcal vEGU 2021 23 Modelling Case 0 Case 1

No signifcant diference between Case 0 and Case 1 for the parameters of interest.

Results vEGU 2021 24 Wide range of reservoir and conduit parameters can explain the depressurizaton rates estmated with geodetc models from March 2015—October 2017. t on increase Seismicity Seismicity 2018 erup LOS displacement (m) displacement LOS Sentnel-1 ascending tme series ALOS-2 ascending interferogram

Results vEGU 2021 25 Case 0 assumes constant rate of depressurizaton, does not constrain change in depressurizaton rate in October 2017.

Hypothesis:

t on Magma replenishment from

increase a deeper source results in Seismicity Seismicity

2018 erup change in depressurizaton LOS displacement (m) displacement LOS Sentnel-1 ascending tme series rate. ALOS-2 ascending interferogram

Results vEGU 2021 26 Case 2: ‣ Magma replenishment from deeper source ‣ Hydraulic connecton with shallow source established in September 2017 Assume source overpressure ( ) of 10 MPa ‣ ΔPs(t) ‣ Constant hydraulic strength (λ(t)) from September 2017 to December 2018 ‣ Depends on propertes of dike connectng shallow to deep source, which are unconstrained

Theoretcal vEGU 2021 27 Modelling Adapted from Girona et al, 2014 Case 2: ‣ Magma replenishment from deeper source Q ‣ Hydraulic connecton with shallow source established in September 2017 ‣ Assume source overpressure (ΔP (t)) of 10 MPa Gas Plume s ‣ Constant hydraulic strength (λ(t)) from September 2017 to December Adapted from 2018 Girona et al., ‣ Depends on propertes of dike connectng shallow to deep source, 2014 k which are unconstrained μ Conduit L dVrep(t) β c Shallow = λ(t)(ΔPs(t) − ΔP(t)) Reservoir dt Rc Vr, α D n r P(t) kr

? M

Rd Deeper magma source

Theoretcal vEGU 2021 28 Modelling Adapted from Girona et al, 2014 Case 2: ‣ Magma replenishment from deeper source Q ‣ Hydraulic connecton with shallow source established in September 2017 ‣ Assume source overpressure (ΔP (t)) of 10 MPa Gas Plume s ‣ Constant hydraulic strength (λ(t)) from September 2017 to December Adapted from 2018 Girona et al., ‣ Depends on propertes of dike connectng shallow to deep source, 2014 k which are unconstrained μ Conduit L dVrep(t) β c Shallow = λ(t)(ΔPs(t) − ΔP(t)) Reservoir dt Rc Vr, α D nr P(t) k r 4 πRd ? M λ(t) = 8Mμnd

Rd Deeper magma source

Theoretcal vEGU 2021 29 Modelling Adapted from Girona et al, 2014 Case 2: ‣ Magma replenishment from deeper source Q ‣ Hydraulic connecton with shallow source established in September 2017 ‣ Assume source overpressure (ΔP (t)) of 10 MPa Gas Plume s ‣ Constant hydraulic strength (λ(t)) from September 2017 to December Adapted from 2018 Girona et al., ‣ Depends on propertes of dike connectng shallow to deep source, 2014 k which are unconstrained μ Conduit L dVrep(t) β c Shallow = λ(t)(ΔPs(t) − ΔP(t)) d Radius of dike R Reservoir V , α t c r connectng D nr P(t) k r 4 deep and πRd shallow ? M λ(t) = reservoirs 8Mμnd Length of dike Parent melt R d Deeper magma source viscosity

Theoretcal vEGU 2021 30 Modelling Adapted from Girona et al, 2014 Case 2: ‣ Magma replenishment from deeper source Q ‣ Hydraulic connecton with shallow source established in September 2017 ‣ Assume source overpressure (ΔP (t)) of 10 MPa Gas Plume s ‣ Constant hydraulic strength (λ(t)) from September 2017 to December Adapted from 2018 Girona et al., ‣ Depends on propertes of dike connectng shallow to deep source, 2014 k which are unconstrained μ Conduit L dVrep(t) β c Shallow = λ(t)(ΔPs(t) − ΔP(t)) d Radius of dike R Reservoir V , α t c r connectng D nr P(t) k r 4 deep and πRd shallow ? M λ(t) = reservoirs 8Mμnd Length of dike Parent melt R d Deeper magma source viscosity No constraints Theoretcal vEGU 2021 31 Modelling ‣ Good ft with pressurizaton rate estmated from geodetc models when either: 1. Large reservoir (~24 km3) and thin conduit (radius ~10 m), or

Results vEGU 2021 32 ‣ Good ft with pressurizaton rate estmated from geodetc models when either: 1. Large reservoir (~24 km3) and thin conduit (radius ~10 m), or 2. Large conduit (radius ~450 m) and medium-sized reservoir (~12 km3)

Results vEGU 2021 33 ‣ Good ft with pressurizaton rate estmated from geodetc models when either: 1. Large reservoir (~24 km3) and thin conduit (radius ~10 m), or 2. Large conduit (radius ~450 m) and medium-sized reservoir (~12 km3) ‣ Hydraulic strength estmated to be λ(t) = 2.1 × 10−7 m3(Pa ⋅ s)−1 ‣ Total volume of magma replenishment at onset of 2018 erupton is ~100 x 106 m3 (vs. >400 x 106 m3 intruded)

Results vEGU 2021 34 ‣ Good ft with pressurizaton rate estmated from geodetc models when either: 1. Large reservoir (~24 km3) and thin conduit (radius ~10 m), or 2. Large conduit (radius ~450 m) and medium-sized reservoir (~12 km3) ‣ Hydraulic strength estmated to be λ(t) = 2.1 × 10−7 m3(Pa ⋅ s)−1 ‣ Total volume of magma replenishment at onset of 2018 erupton is ~100 x 106 m3 (vs. >400 x 106 m3 intruded) ‣ Additonal observatons needed to constrain reservoir volume and conduit radius

Results vEGU 2021 35 Conclusions and Perspectves Jan 2016 Dec 2018 ‣ Magma replenishment from depth may explain change in reservoir pressurizaton rate in late 2017 at Ambrym ‣ Replenishment did not result in uplif ‣ Magma replenishment consistent with increased number of thermal anomalies before 2018 erupton Sentnel-2 satellite, ESA © Bernard Pelletier Shreve et al., 2019 Nov 2018 Aug 2020 Next steps

‣ Explore efect of magma replenishment on number of lava lakes and lava lake level ‣ Further parametric analysis of factors infuencing magma replenishment rate (host rock propertes, deep source overpressure, 2 km hydraulic strength, etc.)

Conclusion vEGU 2021 36 References

P. Allard, A. Aiuppa, P. Bani, et al. Prodigious emission rates and magma degassing budget of major, trace and radioactve volatle species from Ambrym basaltc volcano, Vanuatu Island arc. Journal of Volcanology and Geothermal Research, 304:378–402, 2015. htps://doi.org/10.1016/ j.jvolgeores.2015.10.004.

S.A. Carn, V.E. Fioletov, C.A. Mclinden, C. Li, and N.A. Krotkov. A decade of global volcanic SO2 emissions measured from space. Scientfc Reports, 7:1–12, 2017. ISSN 20452322. htp://doi.org/10.1038/srep44095.

V. Cayol, Y. Fukushima, F. Dabaghi, et al. DefVolc: tools for 3D inverse modelling of deformaton data. htps://doi.org/10.18145/defvolc.

T. Girona, F. Costa, C. Newhall, and B. Taisne. On depressurizaton of volcanic magma reservoirs by passive degassing. Journal of Geophysical Research : Solid Earth, 119:8667– 8687, 2014. htps://doi.org/10.1002/2014JB011368.

Global Volcanism Program. Report on Ambrym (Vanuatu). Weekly Volcanic Actvity Report, 30 August-5 September 2017, 2017. htps:// volcano.si.edu/showreport.cfm?doi=GVP.WVAR20170830-257040.

Y. Moussallam, E. Médard, G. Georgeais, et al. How to turn of a lava lake? A petrological investgaton of the 2018 intra-caldera and submarine eruptons of Ambrym volcano. Bulletn of Volcanology, 83(36), 2021. htps://doi.org/10.1007/s00445-021-01455-2.

M. Sambridge. Geophysical inversion with a neighbourhood algorithm – II. Appraising the ensemble. Geophysical Journal Internatonal, 138(2):727–746, 1999b. ISSN 0956540X. htps://doi.org/10.1046/j.1365-246x.1999.00900.x.

T. Shreve, R. Grandin, M. Boichu, et al. From prodigious volcanic degassing to caldera subsidence and quiescence at Ambrym (Vanuatu): the infuence of regional tectonics. Scientfc Reports, 9(18868), 2019. htps://doi.org/10.1038/s41598-019-55141-7.

Z. Yunjun, H. Fatahi, and F. Amelung. Small baseline InSAR tme series analysis: Unwrapping error correcton and noise reducton, Computers & Geosciences, 133(104331), 2019. ISSN 0098-3004. htps://doi.org/10.1016/j.cageo.2019.104331. References vEGU 2021 37 Thank you for your interest!

vEGU 2021 38