¿Qué desencadena las erupciones de los volcanes de Galápagos? Nuevos objetivos en el Volcán Alcedo : caracterización volcán-física de los productos de las erupciones riolíticas del volcán Alcedo, archipiélago de Galápagos.

Abstract

The Alcedo volcano is a basaltic shield volcano that recorded rhyolitic eruptions with lava flows within the caldera and pumice fall deposits on the east coast of the volcano. This study presents stratigraphic analyses that allow characterizing the distribution of rhyolitic products from the Alcedo volcano, along with high-resolution cartography in a craters and lava flows area at southwest of the caldera. This serves as a base for calculating volcano-physics parameters of the rhyolitic eruption. A field mission was developed, obtaining stratigraphical information from the coast, identifying three layers (A, B and C) of the pyroclastic deposit and four components: dense and frothy pumice (layers A, B and C), a mixture of scoria and pumice (layers A and C), and scoria (layer C). Density tests on the eruption’s pyroclasts revealed a volume-weighted average of de 0.46 g cm-3 for layer A, 0.27 g cm -3 for layer B and 0.37 g cm-3 for layer C, consistent with the compositions of components in each layer. Thickness measurements along the coast were used to extrapolate six isopachs of the Alcedo volcano explosive eruption, estimating a subaerial deposit volume of 1 250 Mm3 and a total volume of 1 960 Mm3. Cartography of the lava flows, developed with very high-resolution digital elevation models (~10.1- 10.3 cm/px), shows the presence of a small crater from which an obsidian flow emerged, a large crater associated with the explosive eruption, and a second small crater from which a later flow of unknown composition emerged and was identified for the first time in this study. The total volume estimation for lava flows is 36 ± 19 Mm3, with an average thickness of 22 ± 11 m. The calculations, along with cartographic products, are valuable for determining the dimensions of the Alcedo volcano explosive eruption, the size of rhyolitic flows, and providing a chronological estimation of eruptive events based on the morphology of the study area.