Iniciar sessão

Navegar para Cima
Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
Última hora:

Painéis ► em encontros internacionais


Referência Bibliográfica

POTUZAK, M., MANGIACAPRA, A., KUEPPERS, U., RICHARD, D., DINGWELL, D.B., ORSI, G., YIRGU, G., DELL'ERBA, F., DI VITO, M.A. (2006) - The Da'ure' eruption at the Boyna Volcanic Complex during the September 2005 Afar extension episode: petrophysical characterisation and eruptive implications. AGU Fall Metting, San Francisco, USA, 11 - 15 de Dezembro (Poster).


Rifting is a common though rarely observed process on Earth. As a consequence, our understanding of the related processes is far from complete. The 2005 rifting event in Ethiopia was the largest subaerial event since more than 2 decades and was accompanied by a small volume volcanic eruption. The pyroclast distribution was very restricted and allows a nearly complete picture of the erupted products. We analysed the petrophysical properties of erupted bombs and ash and the final dome extrusion period. Our data constrain the conditions extant during this comenditic eruption and may thereby provide a unique contribution to the dynamics of dike injection in this rift segment, as measured chemically from the top. A series of microprobe analyses revealed a comenditic glass composition (peralkaline rhyolite) of the eruptive products with 74 wt.% SiO2 and 2.6 wt.% Fetot. The crystal content is very low (approx. 1 %). Differential scanning calorimetry (DSC) technique was applied to glasses from bread-crust-bomb fragments, ash and dome lava. Ash and bread-crust bomb samples exhibit similar cooling rates close to 6 K/min, the dome showed cooling rates an order of magnitude lower. Furthermore, our DSC measurements confirm that the crystallization of Si-rich melts could be avoided even when the cooling rates are very slow. The Tg peak of ash samples was found to be at 1035 +/- 10 K, the bomb samples at 917 +/- 10 K, and the dome rocks at 850 +/- 10 K. This finding is most likely due to the eruption dynamics dependent grain-size and the resulting cooling rates. In addition, the high-T viscosities have been measured using the concentric cylinder method in air. The low-T subliquidus viscosities were provided on glassy samples, previously quenched on stainless steel plate, using the micropenetration method in an Argon atmosphere. The viscosity values show non-Arrhenian behaviour across the whole temperature range investigated and can be fitted by the Avramov equation. The fragility of the melt was calculated. These results constrain temperatures, strain rates and degassing kinetics extant during rare peralkaline volcanic eruptions. These raise a number of questions regarding the underlying magmo- tectonic events presumably responsible for the eruption.