Effects of magma compressibility on volcano deformation and seismicity. Eleonora Rivalta

Transcription

1 Effects of magma compressibility on volcano deformation and seismicity Eleonora Rivalta

2 Outline Interaction between magma-filled deformation sources: 1) Magma chamber dyking 2) Magma chamber magma chamber 3) Dyke faulting and the role played by compressibility in the dynamics of these interactions.

3 1 -The 'missing magma' problem: the 1997 intrusion at Kilauea Dike: m3 Summit: m3 Makahopuhi: m3 Pu'u O'o: m3 V dyke rv= Δ V chamber = 3.8 (Owen et al., 2000)

4 The 2007 'father's day' intrusion Summit: m3 Dike 1: m3 Pu'u O'o: m3 Dike 2: m3 Pu'u O'o lake: m3 (Montogomery-Brown et al., 2010, JGR) rv = 3.0

5 The 2007 intrusion at Kilauea (Montogomery-Brown et al., 2011)

6 The 'missing magma' problem: the 2005 intrusion in Afar Wright et al., 2006

7 The 'missing magma' problem: the 2005 intrusion in Afar V dyke rv= Δ V chamber km 3 =5 ( )km Wright et al., 2006

8 Interpretation An additional source, too deep to be detected from deformation signals, fed the intrusion from below. In general, difficult to test/falsify Volume determinations are not reliable Not to the extent required to explain these discrepancies Magma compressibility Different source compliance

9 Effects of magma compressibility on volcano deformation Árnadóttir et al., 1998 Pressure variation and volume change at the Krafla magma reservoir Magma compressibility and elastic response of host rock mask the 'true volume' of the intrusion Appl. to volume budget of 1984 intrusion at Krafla Johnson et al., 2000 Considerations on the different volumes involved Tryggvason, 1981 Johnson, 1992 Application to the relation between erupted and deflation volumes at Mount St. Helens Rivalta and Segall, 2008 'Mass conservation', volume budget during intrusion events Dynamics of coupling between magma chambers Rivalta, 2010 and dikes Mastin et al., 2008

10 Physical model dm =ρ dv +V d ρ=(ρ dρ dv +V )dp=ρ V (βe +βm )dp dp dp Magma compressibility: 1 dρ βm = ρ dp βm = Pa 1 (or much higher if magma contains bubbles) Source compliance: βe = 1 dv V dp β e (spherical chamber )= Pa 1 4μ βe (penny shaped crack )= Pa pi σ

11 Physical model dm =ρ dv +V d ρ=(ρ dρ dv +V )dp=ρ V (βe +βm )dp dp dp Pa 1 4μ 1 β e (cigar shaped chamber )= μ 1 βe (penny shaped crack )= i 10 7 Pa 1 p σ βe (ellipsoid ) depends on the aspect ratio β e (spherical chamber )= βm = Pa 1 (or much higher if magma contains bubbles) (Amoruso and Crescentini, 2009) If total mass is constant i βm V rv= =1+ βe ΔVc Rivalta and Segall, 2008

12 Physical model Rivalta and Segall, 2008

13 The 'missing magma' problem: chronology Year location rv Ref 1984 Krafla (Iceland) Kilauea (Hawaii) 3.8 (Owen et al., 2000) 2000 Miyakejima (Japan) 3.6 (Irwan et al., 2006) 2004 Dallol (Ethiopia) 32 (Nobile et al., 2012, subm.) 2005 Manda-Harraro (Ethiopia) Kilauea (Hawaii) Ferdinandina (Galapagos) Ferdinandina (Galapagos) 2.0 (Árnadóttir et al., 1998) (Wright et al., 2006, Grandin et al., 2009) (Montgomery-Brown et al., 2011) (Bagnardi and Amelung, 2012, subm.)

14 Wright et al., 2012

15 The 2005 dike intrusion in Afar Ayele et al., 2009

16 The 2005 dike intrusion in Afar ΔV Chambers: km km3 ΔV Dike: +1.5 km^3 ΔV Dike / ΔV Chambers = r_v = km ΔV Chambers: km km3 ΔV Dike: +2.0 km3 r_v = 2.2 Grandin et al., 2009

17 Fernandina, Galapagos rv = 2.6

18 Fernandina, Galapagos rv = 2.0

19 Dallol, Ethiopia, 2004 (Nobile et al., 2011)

20 Dallol, Ethiopia

21 The 1997 intrusion at Kilauea (Owen et al., 2000)

22 The 'missing magma' problem in volcano deformation ~ 0.3 km/h ~ 2 km/h Einarsson and Brandsdottir, 1978

23 Izu Islands (Japan), 2000 Irwan et al., 2006

24 Physical model On one hand: dm On the other hand: dm i =k pc p i dt dm dp =ρ V (βe +βm ) dt dt ρ πr For a cylindrical conduit k= m L long and with radius R: 8 ηl dm c = k p c p i dt 4 (Pinel and Jaupart, 2003) 3 dp i p i p c =, dt = 8 L m V i e m m R 4 8 L r 1 sphere= 4 m 3 R4 ~ weeks to months 64 1 L a p.s.c.= 3 R 4 3

25 Physical model dp i 1 = p p c dt i i dp c 1 = p p c dt c i pc p dm c 1 c Out pi The flow will stop when pc=pi=peq dm i =0 c c 1 c 1 Chamber's volume loss: V =V c p p eq e Dike's volume: b V= p 1 e 1 W E dike b W = sphere = c V 1 m c i t W i 2010 W c Rivalta, = 1 W 1 W W t W W = V c p 1 e 1 W E c 1 t W i m V r V= =1 c c V at any time!

26 Physical model Different time scales for discharge and recharge Convexity upwards Strong dependence on βm, βc i m V r V= =1 c c V at any time! Rivalta, 2010

27 Validation: 2000 intrusion at Izu Islands Rivalta, 2010

28 Validation: 2000 intrusion at Izu Islands Rivalta, 2010

29 Pattern of induced seismicity Keir et al., 2009 Belachew et al., 2011

30 'Vertical' dike propagation (Battaglia et al., 2011, JVGR) (Bonforte et al., 2008, JGR)

31 Vertical propagation and stacked sills (Sigmundsson et al., 2010)

32 Harrat Lunayyir, Saudi Arabia, 2009 (Pallister et al., 2011, Nature Geoscience)

33 2 - Interacting magma chambers

34 Interacting magma chambers (Pascal et al., 2012, submitted)

35 Interacting magma chambers Perspectives: Varying shapes Interacting sources (e.g. boundary elements) Include magma properties (compressibility) Dynamics of filling/emptying

36 3 - Magma compressibility and dyke-faulting interaction

37 Magma compressibility and dyke-faulting interaction Δ σ+δ σ F u i + u i x x Δσ uxi V

38 Magma compressibility and dyke-faulting interaction ( MT fault =μ A f 0 sin2 θ cos2 θ 0 cos2 θ sin2 θ ( ) μδu j λ Δu μ Δuk MT Δ dike =A d μ Δ u j (λ+2μ)δ u 0 0 λ Δu μ Δ uk )

39 Magma compressibility and dyke-faulting interaction

40 Magma compressibility and dyke-faulting interaction Induced earthquakes interact with dykes, which respond with a shearing and change of opening. Apparent rotation of the fault planes (up to ~27 degrees) For low gas content & mass constant, pure DC For higher gas content, significant isotropic and CLVD component CLVD is physical: contraction/inflation of the dyke during the earthquake

41 Perspectives Effects of compressibility are multifaceted and not intuitive It helps thinking about 'mass' rather than volume How much of the recurrent volume-multiplications observed during dyking is due to magma compressibility and source compliance? More statistics will help us find/understand patterns: sill/dyke, magma composition, volatile content, depth of sources, geometry? insight into plumbing at depth Dynamics of the plumbing We need to understand more the influence of gas (bubble nucleation, exsolution, type of degassing) on the observables (deformation, seismicity)

42 Acknowledgements Paul Segall Francesco Maccaferri Maurizio Bonafede Luigi Passarelli Torsten Dahm Yosuke Aoki Emily Montgomery-Brown Marco Bagnardi Larry Mastin Valerio Acocella Tim Wright Derek Keir Karen Pascal Carolina Pagli Adriano Nobile

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