The morphology and evolution of the Stromboli 2002–2003 lava flow field: an example of a basaltic flow field emplaced on a steep slope

Abstract

The use of a hand-held thermal camera during the 2002-2003 Stromboli effusive eruption proved essential in tracking the development of flow field structures and in measuring related eruption parameters, such as the number of active vents and flow lengths. The steep underlying slope on which the flow field was emplaced resulted in a characteristic flow field morphology. This comprised a proximal shield, where flow stacking and inflation caused piling up of lava on the relatively flat ground of the vent zone, that fed a medial-distal lava flow field. This zone was characterized by the formation of lava tubes and tumuli forming a complex network of tumuli and flows linked by tubes. Most of the flow field was emplaced on extremely steep slopes and this had two effects. It caused flows to slide, as well as flow, and flow fronts to fail frequently, persistent flow front crumbling resulted in the production of an extensive debris field. Channel-fed flows were also characterized by development of excavated debris levees in this zone . Collapse of lava flow fronts and inflation of the upper proximal lava shield made volume calculation very difficult. Comparison of the final field volume with that expecta by integrating the lava effusion rates through time suggests a loss of~70% erupted lava by flow front crumbling and accumulation as debris flows below sea level. Derived relationships between effusion rate, flow length, and number of active vents showed systematic and correlated variations with time where spreading of volume between numerous flows caused an otherwise good correlation between effusion rate, flow length to break down. Observations collected during this eruption are useful in helping to understand lava flow processes on steep slopes, as well as in interpreting old lava-debris sequences found in other steep-sided volcanoes subject to effusive activity.

Lava effusion — A slow fuse for paroxysms at Stromboli volcano?

“…Using these values, the 2002-2003 DRE volume was ~ 9.9 ± 2.0 × 10 6 m 3 based on the estimate of (Calvari et al, 2005a) and (Calvari et al, 2005b), comparable with the 8.7 ± 1.8 × 10 6 m 3 derived by photogrammetry (Baldi et al, 2008). To avoid complications arising from uncertainties in vesicularity, in the following analysis we use the effusion rate data derived from thermal imagery acquired from satellite and airborne platforms ( [Calvari et al, 2005a], [Calvari et al, 2005b], [Calvari et al, 2010], and [Lodato et al, 2007]). These yield time-series of the cumulative volumes erupted before both 2003 and 2007 paroxysms.…”

“…« 10 6 m 3 (Bertagnini et al, 1999), reflect the critical balance between magma storage, crystallisation, degassing, and pressure evolution. ( [Calvari et al, 2005a], [Calvari et al, 2005b] and [Lodato et al, 2007]) resulted in a paroxysm after ~ 3 months of lava effusion, whereas a mean eruption rate of 1.5 m 3 s − 1 in 2007 (Calvari et al, 2010) produced a paroxysm after only two weeks. So long as the volcano maintains its present subsurface storage configuration, we infer that it will be possible to use the same threshold volume to forecast future explosive paroxysmal events.…”

“…Error budgets for the effusion rates are comparable for both the helicopter surveys and satellite imagery (± 40%, [Calvari et al, 2005a] and [Calvari et al, 2005b]). (Calvari et al, 2005a), (Calvari et al, 2005b), (Lodato et al, 2007) and (Calvari et al, 2010) From Figure 3, we derived the DRE cumulative volumes erupted before both paroxysms (Fig. 4).…”

“…However, the two most recent Stromboli paroxysms appear to be associated with slow decompression, because the depressurisation and lava effusion took place over a period of days/weeks. Here, we develop this hypothesis further through an analysis of effusion rate data from the 2002([Calvari et al, 2005a, [Calvari et al, 2005b], and [Lodato et al, 2007]) and 2007 eruptions (Calvari et al, 2010). We evaluate these observations in the light of studies and laboratory experiments and propose a triggering mechanism for paroxysms that occur during basaltic effusive eruptions.…”

“…The new model might be the key to understanding how the shallow supply system works, and because it is linked to surface observations of lava effusion, and thus to erupted lava volumes, it could pave the way to forecasting of future paroxysms. [Bonaccorso et al, 2003], [Burton et al, 2008], [Calvari et al, 2005a], [Calvari et al, 2005b], [Calvari et al, 2006], [Calvari et al, 2010], , [Lodato et al, 2007], [Neri and Lanzafame, 2009] and ).…”