Research ArticleGEOPHYSICS

Stress inversions to forecast magma pathways and eruptive vent location

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Science Advances  31 Jul 2019:
Vol. 5, no. 7, eaau9784
DOI: 10.1126/sciadv.aau9784
  • Fig. 1 Numerical Finite Elements (FE) models of principal stress orientation and resulting magma trajectories.

    σ3 is represented by the black segments, the thick red line represents the location of a sill-shaped pressurized melt lens, and the thin red lines represent σ3-orthogonal streamlines. (A) “Unloading scenario” where we applied 9 MPa of vertically oriented tensional stress due to overburden removal (blue arrows). (B) “Inflating sill scenario” where we applied 5 MPa pressure to a thin flat cavity. (C) “Unloading + inflating sill” scenario where we combined the two previous cases. We added a weak (1 MPa) horizontal stretching to all models.

  • Fig. 2 Eruptive history of the Campi Flegrei caldera during the last 15 ka.

    (A) Shaded relief map of the caldera with location of eruptive vents (31). (B) Boxplot showing the radial distribution of eruptive vents. The boxes have horizontal lines at the first quartile q1, median, and third quartile q3. The whiskers correspond to 99.3% data coverage. The red circle at epoch 1 is an outlier [i.e., data point that is smaller than q1 − w × (q3 − q1), where w is the whisker length]. The horizontal size of the boxes represents the time interval of the epoch. (C) Volume of eruptions and cumulative (gray line) erupted volume (31).

  • Fig. 3 Forward model.

    Summary of the resampled Monte Carlo simulations shown as histograms for epoch 1 (red), epoch 2 (green), and epoch 3 (blue). Gray and colored bars refer to simulations where σt is larger and smaller than 2PU/π, respectively, corresponding to “shrinking magma chamber” and “unloading controlled” scenarios. (A to D, F to I, and K to N) The resampled distributions for the input parameters as indicated. (E, J, and O) Representative streamlines for the two scenarios and the frequency of observed eruptive vents in the upper part of the panel.

  • Fig. 4 Vent forecasts.

    Top: Stationary stress forecast. (A) Thin red lines are forecasted magma trajectories, and red stairs indicate the distribution of arrival radii based on 66% of the observed vents of epoch1. The blue and red bars show the distribution of observed vents and a random 66% of them, respectively. (B and C) Marginal distributions of inverted PU and σT/PU (red bars) fitted by beta functions (magenta lines), respectively. Bottom: Evolving vent forecasts. (D) Observed vent radii and resampled trajectories for epoch 1 [we excluded the outlier vent of Rione Terra (caldera center)]. (E and F) Resampled distributions of PU and σt/PU for epoch 1 fitted with a generalized beta function [magenta lines for (E), (F), (H), and (I)]. (G to I) Same as (D) to (F) but for epoch 2. (J and K) Distributions for PU and σt/PU projected for epoch 3. (L) Vent forecasting for epoch 3 (gray stairs) compared with observed vent radii (blue bars). (M to O) Same as (G) to (I) but for the Monte Nuovo cone.

  • Fig. 5 Explaining asymmetric volcanism.

    (A and B) Topographic/loading profiles (A, magenta and blue lines, respectively) and modeled stress field below Campi Flegrei caldera for the two half cross sections highlighted in the inset of (B). The black segments represent the direction of σ3. The thick red line represents the pressurized melt zone according to (38) and likely active in the last 5 ka at least (33). Thin red lines are σ3-perpendicular streamlines. Elev. a.s.l., elevation at sea level.

  • Fig. 6 Performance of the unloading model for notable worldwide calderas.

    The background color represents the phase diagram for intracaldera, rim, or off-caldera vent location according to model prediction, as specified. The caldera rim field is bounded by 0.85a and 1.15a (inset). Estimates for calderas in nature are represented by pie plots according to the proportion of observed intracaldera, rim, or off-caldera vents, with the same color coding as the background. Uncertainties are shown as black lines. The star highlights the position of Campi Flegrei (CF) according to the σt/PU calculated in this study. The inset shows streamlines of selected models with d/a = 0.4 and d/a = 1.4 and variable σt/PU as a reference. d/a is depth d normalized to the caldera radius a, while σt/PU is the normalized stress controlling trajectory concavity. Caldera acronyms are as follows: FE, Fernandina; WO, Wolf; DA, Darwin; SiN, Sierra Negra; AL, Alcedo; CeA, Cerro Azul; AS, Aso; CrL, Crater Lake; RO, Rotorua; SA, Santorini; BO, Bolsena; RA, Rabaul; AI, Aira; VA, Valles; DO, Dolomieu.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaau9784/DC1

    Fig. S1. Probability distributions for model parameters of epoch 1.

    Fig. S2. Probability distributions for model parameters of epoch 2.

    Fig. S3. Probability distributions for model parameters of epoch 3.

    Fig. S4. Covariance distributions of σt/PU versus PU and σt versus PU for a set of simulations with starting depth homogeneously distributed between 3 and 4 km and radius equal to 0 km.

    Fig. S5. Impact of variability of starting depth.

    Fig. S6. Parameters projection for the time-varying stress forecast.

    Table S1. Thicknesses and densities of deposits filling Campi Flegrei caldera with associated loads.

    Table S2. Properties of notable worldwide calderas.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Probability distributions for model parameters of epoch 1.
    • Fig. S2. Probability distributions for model parameters of epoch 2.
    • Fig. S3. Probability distributions for model parameters of epoch 3.
    • Fig. S4. Covariance distributions of σt/PU versus PU and σt versus PU for a set of simulations with starting depth homogeneously distributed between 3 and 4 km and radius equal to 0 km.
    • Fig. S5. Impact of variability of starting depth.
    • Fig. S6. Parameters projection for the time-varying stress forecast.
    • Table S1. Thicknesses and densities of deposits filling Campi Flegrei caldera with associated loads.
    • Table S2. Properties of notable worldwide calderas.

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