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Earth, Planets and Space
Fig. 3 | Earth, Planets and Space

Fig. 3

From: Salt shell fallout during the ash eruption at the Nakadake crater, Aso volcano, Japan: evidence of an underground hydrothermal system surrounding the erupting vent

Fig. 3

A schematic diagram of the formation process of salt fallouts. a A hydrothermal solution distributed beneath the crater floor surrounding the eruption vent. The hydrothermal solution sporadically pours into the conduit of the eruption plume or the gas plume, beneath the vent. b The poured solution forms droplets and is then transported by the plume. Heating of the droplet in the plume evaporates the water, precipitating the salts at the droplet surface. A complete drying of the droplet creates a hollow spherical salt shell. Preservation of the fragile, hollow spherical salt shell structure during transport suggests that the salt formation occurs after magma fragmentation, implying that the hydrothermal solution layer is located at a depth shallower than the magma fragmentation level

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