Abstract

ELIZONDO, Verónica; ALVARADO, Guillermo E.  and  SOTO, Daniel. Space-time evolution of eruptive mouths on the volcanoes Irazú, Arenal, Turrialba and Poás in historical time (Costa Rica). Rev. Geol. Amér. Central [online]. 2019, n.61, pp.35-57. ISSN 0256-7024.  http://dx.doi.org/10.15517/rgac.v61i0.40087.

Historical research was performed analyzing the morphologic and temporary evolution of the craters and small eruptive vents (lateral craters, intracraters, some as pit craters and small craters or “mouths”) of the volcanoes Irazú, Arenal, Turrialba and Poás. The establishment of the small intracrateric eruptive mouths was preceded by fumarolic activity in the summit, where location seems to be controlled by the same tectonic guidelines that predominate at the volcanic edifice or massif: NW-SE, E-W and N-S (Irazú), E-W (Arenal), NE-SE (Turrialba) and N-S (Poás). The initial formation of the intracraters at Irazú and its coalescing was ruled dominated by phreatic activity with phreatomagmatic phases (1917-1921, 1924, 1928-1930, 1933, 1939-1940), which culminated with eruptive activity from 1962 to 1965, in presence of abundant juvenile pyroclasts (strombolian and vulcanian activity), to finally establishing a main crater that encompasses the smaller craters. On Arenal’s western flank, three new craters formed in 1968 in the E-W fissure. Between Irazú’s eruptive period in 1723 and its reactivation in 1917, 194 years passed, similar to Turrialba’s 144 years of relevant inactivity between 1866 and 2010. Turrialba showed the formation of minor vents between 2010 and 2013, to culminate with the enlargement and deepening of the active crater (2014-2019) with various minor active intracraters. The 2017 activity at Poás volcano was also preceded by phreatic activity with the formation of mud volcanoes, which ended with the volcanic dome’s destruction by phreatomagmatic explosions. The birth of a new spatter cone at the same place of the former dome, as well as various sulfur cones and mud volcanoes oriented approximately N-S. In this paper, certain patterns in the succession of craters in the cases mentioned and their relationship with the tectonic trends may have short-term implications for the volcanic hazard once the preferential sectors of evolution and formation are known, as well as the evolution from small crater to larger ones, related to more vigorous eruptive periods.

Keywords : Eruptive small vents; volcanic craters; Irazú, Arenal, Turrialba and Poás volcanoes; morphological evolution; Costa Rica..

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