Figure 4
From: Low efficiency of large volcanic eruptions in transporting very fine ash into the atmosphere
Simulations of the tephra fallout deposit from the 23rd February 2013 Etna eruption. The simulations are generated by the FALL3D tephra-transport deposition model with distinctive Qs as input. The simulated tephra fallout deposits are displayed as isomass contour levels (black lines) that represent the “computed tephra load” on the ground in kg/m2. The “measured tephra load” on the ground is indicated in red squares at individual locations of field sampling (red squares and numbers, see Supplementary Information Table 3 for details on sampling locations). (a) Simulation 1 uses an input Qs1 estimated with our satellite-derived statistical model (see equation at the top of the map for low SiO2 content and open system). The simulated deposit is in very good agreement with the “measured tephra load” at locations #1, 8, 9 and 10 for instance. (b) Simulation 2 uses an input Qs2 estimated with the empirical scaling law35 (see equation at the top of the map). The simulated deposit has a much smaller extent than in simulation 1, with “computed tephra loads” departing significantly from the “measured tephra loads”. The total erupted mass (TEM) according to these simulations yields values of 1.09 × 1010 and 6.58 × 108 kg for simulation 1 and 2, respectively. The reference TEM value47 for this fallout deposit is 4.9 × 109 kg which means that the Satellite-derived statistical model overestimates the TEM by a factor of ∼2.2, while the empirical scaling law underestimates the TEM by a factor ∼7.4.
