Surface deformation of the Barren Island volcano, Andaman Sea (2007–2017) constrained by InSAR measurements: Evidence for shallow magma reservoir and lava field subsidence

Highlights

• InSAR measurements revealed co-eruptive deformation of the cinder cone of the Barren Island Volcano

• Bayesian Inversion of InSAR data suggest exceptionally shallow magma reservoir at a depth of 578 m

• Shallow magma reservoir may be a result of extensional stress regime imposed by the oblique subduction

• Significant deformation (−15 to −150 mm/yr) observed along the lava delta of the Barren Island is interpreted as post-emplacement subsidence

• Quantified thickness and spatial extent of lava flow

Abstract

Barren Island, situated in the Andaman Sea, is the northernmost active volcano of the Sunda arc. The oldest known eruption of the volcano was during the period 1787–1832. After about 150 years of quiescence, volcanic activity resumed in 1991 and continues since then. The magmatic plumbing system of this volcano is largely unknown due to lack of geophysical experiments owing to its remote location. We report, for the first-time, time-series surface deformation measurements of Barren Island volcano from interferometric synthetic aperture radar (InSAR) during epochs 2007–2011 and 2015–2017. Line-of-Sight (LOS) deformation of −50 mm/yr during 2007–2011 at the cinder cone is interpreted as the co-eruptive pressure changes associated with the 2008–2010 eruptions. Bayesian inversion suggests a shallow magma reservoir at a depth of 578₋₁₀₀⁺³⁰⁰ m below the summit. The depth of the magma reservoir is shallower than that of other volcanoes of the Sunda arc, probably due to the extensional stress regime imposed by the oblique subduction. Based on the present studies and previous works, we propose a plausible source model for Barren Island volcano. We also discuss potential biases in the present source parameter estimation due to the lack of high quality InSAR data from both ascending and descending directions. Significant deformation (−15 to −150 mm/yr) observed along the lava delta of Barren Island volcano for both the epochs are interpreted as post-emplacement subsidence of the lava flow. Further, we characterise the lava flow including volcanic deposits by mapping its spatial extent and elevation changes during 1979–2000 and 2000–2017 periods using geodetic measurements.

Introduction

The Sunda arc, formed by the subduction of the Indian plate below the SE Asian plate, hosts more than 80 volcanoes from eastern Java to the Andaman Island (Fig. 1). Barren Island, situated in the Andaman Sea, is the northernmost active volcano of this arc. The volcano rises from a depth of 2000 m to a maximum height of 354 m above the mean sea level. The diameter of the island is about 3 km. The volcano consists of a cinder cone surrounded by caldera wall, which opens towards the west (Fig. 1).

Barren Island volcano is built of prehistoric lava flows along with volcanoclastic deposits (Sheth et al., 2009). Geochemical and isotopic studies suggest that the volcano became sub-aerial at about 1.6 Ma and had major eruptions at 71, 62, 23, 17, 12 and 8 Ka (Ray et al., 2013, Ray et al., 2015; Awasthi et al., 2014). According to historical records, the formation of the cinder cone at the centre of the pre-historical caldera occurred as a result of a series of violent volcanic eruptions during 1787–1832 (Shanker et al., 2001; Luhr and Haldar, 2006). After about 150 years of quiescence, the second phase of volcanic activity resumed around 1991 and several eruption episodes have been recorded since then. Violent eruptions with lava flows were observed during 1991, 1994–95, 2005–2006 and 2008–2010 (Pal et al., 2010; Sheth et al., 2010). After 2010, the volcanic activity has subsided and strombolian activity with ash and occasional lava eruptions continues until the present.

Measurement of surface deformation caused by volcanic activity can provide vital insights into the magma plumbing system and eruption mechanisms. Volcanic systems of the west Sunda and Java regions are well studied using InSAR data (Philibosian and Simons, 2011; Chaussard and Amelung, 2012; Chaussard et al., 2013). However, despite the long eruption history, Barren Island volcano is poorly studied using InSAR and its magma reservoir characteristics are largely unknown. Previous satellite based studies are restricted to optical/thermal image analysis for construing the surface and atmospheric process associated with the volcanic eruptions (Reddy et al., 1993; Vinod Kumar et al., 2006; Martha et al., 2018). We present, for the first time, comprehensive surface deformation data of the Barren Island volcano from InSAR measurements during 2007–2011 and 2015–2017 epochs. We also present a source model for the volcanic deformation using inversion of the InSAR data.