Stress barriers controlling lateral migration of magma revealed by seismic tomography

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.

What Controls Sill Formation: An Overview From Analogue Models

“…Sill emplacement above previous sill may also occur (Rocchi et al, ; Westerman et al, ), as probably due to low rigidity and/or high‐viscosity contrasts due to advanced but not complete solidification of the older sill, or to the lateral feeding of the younger sills, without any interaction with the older magma. Rigidity inversions may be due to thermal weakening (i.e., decrease of rock rigidity; Heap et al, ), so that portions of the crust become more compliant at high depths, as geophysically detected in Afar (Desissa et al, ), Iceland (Mitchell et al, ; Schuler et al, ), and Canary Islands (Martí et al, ).…”

Imaging of Lithospheric Structure Beneath Jeju Volcanic Island by Teleseismic Traveltime Tomography

“…Complex magmatic structures within the lithosphere are generally formed by the movement and emplacement of magmas in the lithosphere (e.g., Benz et al, ; H.‐H. Huang et al, ; Martí et al, ; Miller & Smith, ; Thybo & Artemieva, ). Such magma emplacement and movement are controlled by various factors, including local or regional stress fields and preexisting structural (e.g., fault or fracture) or rheological discontinuities (Maccaferri et al, ; Martí et al, ; Németh, ; Takada, ; Valentine & Perry, ).…”

Driving magma to the surface: The 2011–2012 El Hierro Volcanic Eruption

“…(e) P wave 3‐D tomography of the structure of El Hierro, and its horizontal projection at 17.2–18 km depth (modified from Martí et al . []).…”

“…It revealed a high‐velocity crust to a depth of 10–12 km and a low‐velocity anomaly below the base of the crust, interpreted as a batch of magma rising as a small plume from the mantle located beneath El Hierro. Furthermore, recent P wave 3‐D tomography [ Martí et al ., ] performed with 20,000 local earthquakes registered in September 2011 to March 2014, revealed additional and valuable features. Martí et al .…”

“…Martí et al . [] could model the structural complexity of the interior of El Hierro, including the identification of a number of stress barriers that authors interpreted as corresponding to regional tectonic structures and blocked pathways from previous eruptions, which reduces the options for fresh magma for finding a suitable pathway to the surface and for erupting (Figure e). These authors also confirmed the existence of a magma reservoir in the upper‐mantle, situated in the central area of the island.…”