Dynamic nature of volcanic phenomena: 2001--2002 eruption processes at Etna and Stromboli, Italy

This dissertation identifies and explains fluctuations in eruption at the persistently active basaltic volcanoes of Etna (Sicily, Italy) in 2001 and Stromboli (Aeolian Islands, Italy) in 2002. In the Etna chapter, ∼72 hours of ground-based gas puff frequency and lava flow velocity data are considered alongside ∼8 months of satellite-based effusion rate data. The data suggest oscillations in the shallow supply of magma on timescales of both hours and months.;The Stromboli chapters use microtextural analysis of lapilli samples to identify the presence of three physically distinct magma types (low density, LD; transitional textures, TT; high density, HD) with contrasting vesicle textures. Quantitative vesicularity data indicate that the textures are linked via an ongoing, time-dependant evolution involving increasing degrees of coalescence and outgassing from LD to TT to HD magma. Fine-scale mingling of end-member magma types implies dynamic shallow processes that are linked with the passage of gas slugs through the shallow conduit during Strombolian explosions. New LD magma rises with gas slugs; mingling with HD occurs during and immediately following slug ascent.;A similar textural diversity is documented in six samples from a 2-hour sequence of similar explosions and one explosion ∼24 hours later. This indicates that Stromboli's shallow magma is physically complex at the instant of a single explosion, and that, with minor variation, such physical complexity is likely to persist through sequences of similar explosions (on timescales of hours to days). In comparison, contrasts in the textural properties of ejecta from three periods of more markedly contrasting explosion intensity (May, September/October, December) suggests a feedback between changing rheology of shallow magma and explosion processes (over periods of weeks to months).