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Slug or Plug: Why does Stromboli volcano erupt?

Strombolian eruptions

Figure: Close view of Stromboli volcano erupting molten lava fragments.
Source: Tim Pfeiffer

Stromboli volcano is famous for its relatively mild but astonishingly persistent eruptions. The leading paradigm for these so-called normal eruptions posits that each eruption represents the burst of a large gas slug ascending through liquid magma in the volcanic conduit. However,numerous petrological studies have since established the existence of highly crystalline magma in the upper few hundred meters of the Strombolian conduit.These observations shed doubt on a purely fluid-dynamical view of the conduit dynamics at Stromboli. What are the ramifications of the presence of highly crystalline magma in the upper part of the Strombolian conduit? We suggest that the crystal-rich magma might form a plug with finite yield strength, which is porous enough to allow for substantial amount of passive degassing but not porous enough to allow all ascending gas to escape. As a consequence, gas accumulates underneath the plug and builds up pressure which eventually causes failure of the plug. We  hypothesize that plug failure and associated drainage of gas-right magma might be the cause of normal eruptions.

Collaborators: Kathy Cashman,Isolde Belien, Brad Hager, Per Olof Persson