From prodigious volcanic degassing to caldera subsidence and quiescence at Ambrym (Vanuatu): the influence of regional tectonics

Abstract

Eruptive activity shapes volcanic edifices. The formation of broad caldera depressions is often associated with major collapse events, emplacing conspicuous pyroclastic deposits. However, caldera subsidence may also proceed silently by magma withdrawal at depth, more difficult to detect. Ambrym, a basaltic volcanic island, hosts a 12-km wide caldera and several intensely-degassing lava lakes confined to intra-caldera cones. Using satellite remote sensing of deformation, gas emissions and thermal anomalies, combined with seismicity and ground observations, we show that in December 2018 an intra-caldera eruption at Ambrym preceded normal faulting with >2 m of associated uplift along the eastern rift zone and 2.5 m of caldera-wide subsidence. Deformation was caused by lateral migration of >0.4 cubic kilometers of magma into the rift zone, extinguishing the lava lakes, and feeding a submarine eruption in the rift edge. Recurring rifting episodes, favored by stress induced by the D’Entrecasteaux Ridge collision against the New Hebrides arc, lead to progressive subsidence of Ambrym’s caldera and concurrent draining of the lava lakes. Although counterintuitive, convergent margin systems can induce rift zone volcanism and subsequent caldera subsidence.

The 2017 Eruption of Erta 'Ale Volcano, Ethiopia: Insights Into the Shallow Axial Plumbing System of an Incipient Mid‐Ocean Ridge

“…Several key features of the Erta 'Ale shallow plumbing system show similarities to other volcanoes such as Kilauea and Mauna Loa, Hawaii, and Ambrym, Vanuatu, with the removal of melt from a summit caldera coincident with the horizontal propagation of a dike into an established rift zone (e.g., Amelung et al, ; Montagna & Gonnermann, ; Poland et al, ; Shreve et al, ). At Kilauea, a synthesis of measurements, including InSAR, GPS, tilt, and gravity, reveal a shallow magma reservoir at ∼1.5 km depth below the Halema'uma'u lava lake (Anderson et al, ; Bagnardi et al, ; Poland et al, ).…”

The 2020 Eruption and Large Lateral Dike Emplacement at Taal Volcano, Philippines: Insights From Satellite Radar Data

“…The balance between vertical and lateral propagation is a key question central to many magmatic systems, occurring not only in tectonic spreading centers, such as Krafla, Afar, and Bárdarbunga (Sigmundsson et al., 2015; Sturkell et al., 2006; Wright et al., 2006), but also at ocean islands with localized rift zones such as Kı̄lauea, Ambrym, and Piton de la Fournaise (Froger et al., 2015; Neal et al., 2019; Shreve et al., 2019) and sometimes even at restless calderas such as Campi Flegrei (Di Vito et al., 2016). In these systems, a large volume of magma travels laterally, whether the eruptive sequence starts with an eruption in the central area, as observed at Piton de la Fournaise in 2007 (Froger et al., 2015) and Ambrym in 2018 (Shreve et al., 2019), or without eruption in the central part but deflation due to the lateral dike propagation and distal eruption as found for Bárdarbunga‐Holuhraun, 2015 (Sigmundsson et al., 2015) and Kı̄lauea, 2018 (Neal et al., 2019). However, there are also cases where lateral dike propagation does not feed an eruption (Sturkell et al., 2006; Wright et al., 2006), as in the case of Taal’s 2020 event.…”

“…Two distinct signals emerged: (1) Volcano Island and the north and east portions of Taal caldera experienced deflation of ∼4 m, and (2) the SW region from Volcano Island toward Balayan Bay inflated (∼1 m) and pulled apart (∼2 m), with the center of the NE‐SW trending rift located near the Pansipit river. In volcano geodesy studies, these signals suggest magma withdrawal from a reservoir and magma emplacement through dike intrusion (Neal et al., 2019; Shreve et al., 2019; Sigmundsson et al., 2015; Sturkell et al., 2006; Wright et al., 2006, & references therein).…”

What Triggers Caldera Ring‐Fault Subsidence at Ambrym Volcano? Insights From the 2015 Dike Intrusion and Eruption

“…Little geological trace would be left at the surface, especially if lateral intrusions, which may arrest at depth, were the dominant mechanism of magma withdrawal from a central magmatic plumbing system. Increased space‐geodetic monitoring of volcanoes worldwide improves the chances of measuring caldera subsidence and ring‐fault activation during moderate‐sized eruptions (VEI < 3) (Pinel et al., 2014; Shreve et al., 2019).…”