Abstract

A dacite dome at Unzen volcano grew mainly exogenously when it was small and the effusion rate was high, but endogenously when the dome became large and the effusion rate declined. The endogenous dome that has grown since late 1993 shows a shape classified as “Peléan,” whereas the earlier stage had a “low lava dome” shape. The carapace of the endogenous dome moved like the crust of a basaltic lava pillow, although the dome is several hundred times larger than such pillows. The surface carapace was carried from the inside of the dome where it had been produced, and it thickened as it cooled. The crater floor was strongly deformed by the advancing endogenous dome. The movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground.

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