Abstract
Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011–2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt.
Highlights
Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another
In comparison with other examples occurred in rift zones (e.g.: Iceland, Afar), where magma migrated more or less linearly following the main structural trends of the rifts structures[4,10,11,12], the lateral migration of magma at El Hierro was clearly affected by pre-existing structures that defined stress barriers that controlled its journey inside the volcanic edifice[2,19]
As at the rest of the Canary Islands, the lithosphere at El Hierro volcanic edifice is composed of different main rock layers that from top to base include: the volcanic pile composed of an alternation of lava flows and pyroclastic deposits; a pre-volcanic sediment layer; the pre-volcanic basaltic oceanic crust; and the lithospheric mantle
Summary
Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. In comparison with other examples occurred in rift zones (e.g.: Iceland, Afar), where magma migrated more or less linearly following the main structural trends of the rifts structures[4,10,11,12], the lateral migration of magma at El Hierro was clearly affected by pre-existing structures that defined stress barriers that controlled its journey inside the volcanic edifice[2,19]. A similar pattern of lateral magma migration has been observed in some of the six post-eruptive unrest episodes that have occurred since 2012 (Fig. 2)
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