Explosive dynamics of violent Strombolian eruptions: the eruption of Paricutin Volcano 1943-1952 (Mexico)

Violent Strombolian is a term that was originally used by MacDonald [Macdonald, G.A., 1972. Volcanoes, Prentice-Hall inc., Englewood Cliffs, New Jersey, 510 pp.] to describe energetic Strombolian eruptions such as some of the more explosive phases of the 1943‚Äö-1952 eruption of Par‚àö‚â†cutin Volcano (Michoac‚àö¬8n, central Mexico), eruptions that disperse 'showers of incandescent cinder and bombs...to heights of a few thousand feet' and during which 'a great black ash cloud rises above the volcano'. Here we re-examine accounts of the Par‚àö‚â†cutin eruption and compare them with new stratigraphic data and physical features of the tephra deposit to improve the definition of violent Strombolian activity and to better elucidate the mechanisms that can cause this distinctive eruptive style. We find characteristic violent Strombolian activity to be strongly pulsatory, with production of moderately high eruption columns (2‚Äö-6 km) that eject abundant fine ash. Also characteristic is simultaneous lava effusion from lateral vents. At Par‚àö‚â†cutin, violent Strombolian activity occurred at magma eruption rates of 104 to 105 kg/s, intermediate between Strombolian and subplinian rates. A progressive decline in magma flux during the eruption led to a decrease in the relative proportion of both erupted tephra and glassy vesicular fragments in the fallout layers. Eruption characteristics can be explained by varying degrees of shallow gas segregation from water-rich basaltic magma that modulate both transitions between two-phase flow regimes in the upper conduit and effusion of degassed lava from the base of the cone.