Vertical deformation Seismogram Gravity change The dynamics of magma chamber refilling at the Campi Flegrei caldera A. Longo 1, C. Montagna 1, M. Vassalli 2, P. Papale 1, D. Giudice 1, G. Saccorotti 1 INGV Pisa
New reconstruction of ground deformation at Serapeo (Pozzuoli) during last two centuries Present unrest started in 1950 About 60 years of unrest From Del Gaudio et al., INGV-DPC Project 2004-06/V3_2
Seismic tomography Melt zone at 7-8 km below the surface (from Zollo et al., GRL 2008)
0 0 pressure (MPa) Pressure (MPa) 100 200 300 400 500 Top of carbonatic basement Minopoli 2 Agnano Monte Spina Campanian Ignimbrite Seismic discontinuity Campi Flegrei 4 8 12 16 20 Depth (km) depth (km) From Civetta, Arienzo, Mangiacapra, Moretti, et al., INGV-DPC Project 2004-06/V3_2 0.0 0.2 0.4 0.6 0.8 1.0 CO 2 gas (wt fraction) composition of the gas phase (wt% CO 2 ) pressure (MPa) top of carbonatic basement Top of carbonatic basement Seismic discontinuity Vesuvius depth (km) composition of the gas phase (wt% CO 2 )
Seismic reflection From RU Faccenna, INGV-DPC Project 2004-06/V3_2 Na 09
Plinian phase D1 of the 4100 BP Agnano Monte Spina eruption CO 2 ~ 60-80 wt% in the gas phase 1.5 3 km depth From Rutherford et al., INGV-DPC Project 2004-06/V3_2
Agnano Monte Spina eruption shallow phonolite deep trachyte A few tens of hours before eruption From Rutherford et al., INGV-DPC Project 2004-06/V3_2
Chemical and isotopic evidence of mixing-mingling preceeding many CF eruptions AMS Eruption 19.06 19.05 19.04 206 Pb/ 204 Pb AMS Eruption 19.03 A1 wr E1 wr 19.02 E gray glass 19.01 87 Sr/ 86 Sr 19.00 0.70745 0.7075 0.70755 0.7076 0.70765 AVERNO Eruption 0,707465 IC Eruption SM sp SMs SMc Mond.15U3 0,707415 87 86 Sr/ Sr 0,707365 Mond.152a2 From Civetta et al., INGV-DPC Project 2004 06/V3_2 0,707315 w.r Mg-cpx. big Fe-cpx.small Fe-cpx.big Magn. Feld. big 0,707265 0 1 glass 2 3 Mg-4 5 Fe-cpx.int 6 7 Biot. Feld.frantz 8 9 10 11 Apat 12 13
Global view of the CAMPI FLEGREI system INGV-DPC Project 2004-06/V3_2
CAMPI FLEGREI 0 CO 2 -depleted phonolite - 4 (Project 2004-2006 V3_2) CO 2 -rich shoshonite - 8 km a.s.l. - 12
p t o p = 70 MPa (~3 km) Shallow oblate CO 2 poor phonolite H 2 O 2.5 wt% CO 2 0.3 wt% (Rutherford, 2004, Civetta, pers. comm.) Shallow prolate CO 2 rich shoshonite H 2 O 2 wt% CO 2 1 wt% (D'Antonio et al., 1999) T = 1533 K No crystals Mingling magmas Exsolution law: Papale et al. (2006) Viscosity: Giordano et al. (2008)
Initial physical properties p t o p = 70 MPa (3 km) 6 gas vol%, 2240 kg/m 3 viscosity 620 Pa s 5 gas vol%, 2270 kg/m 3 ρ = 40 kg/m 3 ρ = 20 kg/m 3 10 gas vol%, 2230 kg/m 3 4 gas vol%, 2290 kg/m 3 9 gas vol%, 2270 kg/m 3 3 gas vol%, 2440 kg/m 3 viscosity 420 Pa s p b o t t o m = 210 MPa (9 km)
GALES Developed at INGV Pisa Finite Elements Method Galerkin Weighted Residuals Stabilization: Least Squares (streamwise direction) Discontinuity Capturing (solution gradient direction) Double discretization in space and time Primitive variables (y, p, u, T) C++ programming language Parallel computation (Linux cluster) http://www.pi.ingv.it/~longo ~longo/gales/gales.htmlgales.html Accurate, robust, and adaptable Solves from compressible to incompressible flows Suitable for the simulation of the space-time evolution of magmatic systems in a wide domain (from the deep regions of magma chamber to the volcanic crater)
MAGMA multiphase, multicomponent separated flow phase- and composition-dependent properties Newtonian to non-newtonian rheology phase changes (volatile exsolution, crystallization) multicomponent gas-liquid reactions (H 2 O, CO 2, S, ) kinetics of phase change wide range of flow regimes (incompressible to compressible, low-to-high-re, ) Red: accounted for Black: future implementations
Oblate chamber Evolution of composition
Physical properties at t = 7h 45' Upper chamber: Composition: 100 wt% -> ~70 wt% phonolite Density: 2240-2270 kg/m 3 -> ~2190-2260 kg/m 3 Gas content: 6-5 vol% -> ~8-6 vol% gas ~1 km 130 m/h v max ~1 m/s Mass changes (relative): upper chamber -3 10-3 bottom chamber +3 10-5 v max ~ 0.1 m/s
Prolate chamber Evolution of composition Slower convection/mixing lower density contrast larger friction in the chamber
Upper chamber ~ 8 hours -0.25 bars 0 bars overpressure -0.35 bars -0.2 bars -0.4 bars -0.3 bars overpressure Lower chamber +1 bar
~ 8 hours overpressure prolate oblate Chamber top overpressure prolate oblate Chamber middle overpressure prolate oblate Chamber bottom
Mass of shoshonitic magma entering the shallow chamber oblate prolate
Conclusions The buoyant magma invading the shallow chamber soon looses its identity as a separate component (in optimum agreement with the observations) The geometry of the shallow chamber has large effects on the dynamics of magma refilling and mixing: Oblate: faster / more efficient Prolate: slower / less efficient The pressure evolves in a complex way, overall decreasing in the shallow chamber, and increasing in the deep chamber At least in the oblate chamber case, the pressure decrease in the shallow system is partially recovered over the range of ~10 hours, letting however a residual negative overpressure of the order of a few tenths of a bar