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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

PIMENTEL, A., SPARKS, R.S.J., PACHECO, J.M. (2004) - Morphology and petrology of silicic lava flows and lava domes of Terceira Island (Azores). 4th Workshop of the Volcano Dynamics Research Training Network (VDRTN) - “Basaltic Volcanism”, Ilha da Reunião, França, 10 - 20 de Maio (Poster).​


Terceira Island has numerous recent effusive silicic products produced by the Santa Barbara and Pico Alto polygenetic volcanoes. Silicic extrusions occur in the calderas and on the flanks, sometimes along WNW-ESE to NW-SE alignments. Aerial-photograph analyses and field-work allowed to identify 151 effusive silicic vents on three of the four central volcanoes of the island. Overall, 110 lava extrusions were analysed: 68 lava domes (mainly low lava domes) and 42 silicic lava flows (coulees). These silicic extrusions have aspect ratios ranging from 4 to 48. The morphometric data shows good linear and power-law correlations between volume, height/thickness and radius/length, although with lower correlation coefficients for the lava flows.


Terceira’s silicic lavas have a relatively narrow compositional range and similar crystal content. The petrologic data suggest that the composition and the crystal content do not play a key role in the resulting type of the extrusion.


The total extruded volume and underlying surface slope are not main factors controlling the type of theses silicic extrusion. The main factor influencing of the shape of the lavas is the effusion rate.