Morphological evolution of a new volcanic islet sustained by compound lava flows

Fukashi Maeno,Takayuki Kaneko,Setsuya Nakada

doi:10.1130/g37461.1

Abstract

We investigated the creation of a volcanic islet and emplacement of lava flows in the sea by analyzing data from the island-forming eruption at Nishinoshima, Japan, that has been continuing since November 2013. Aerial observations and satellite images were used to perform a quantitative analysis of the eruption processes. The most intriguing characteristic of the lava flows is the development of lobes and tubes from breakouts and bifurcations of andesitic ‘a’ā-type lava flows. Internal pathways that fed lava to the active flow front were eventually developed by crust solidification and dominated the lava transport. The average discharge was ~2 × 10 5 m 3 /day, and the total volume of erupted material reached ~0.1 km 3 at the end of February 2015. Fractal analysis of the lava-flow margins suggests that the growth pattern is self-similar, with a fractal dimension (D) of ~1.08–1.18, which is within the range of subaerial basaltic lava flows. The morphological evolution of Nishinoshima is controlled primarily by effusion of lava with an apparent viscosity of 10 4 –10 6 Pa∙s, average discharge of ~2.3 m 3 /s, and eruption duration lasting ~2 yr. Our data and analyses suggest that the effect of lava coming in contact with seawater, as well as the variations in the lava discharge rate on local and overall scales, are important factors affecting the development of crust and the lava transport system.

Highlights

Lava-flow morphology reflects the emplacement and cooling dynamics of erupted lava, and is used to constrain eruption parameters, ambient conditions, and the physical properties of lavas (e.g., Huppert et al, 1982; Griffiths, 2000)
Subaerial lava flows and their eruption processes are often recorded by monitoring instruments, and eruption parameters such as the discharge and its temporal variation are measured quantitatively (e.g., Harris et al, 2007)
We describe the eruption process and the morphological evolution of the lava flows that form a new volcanic islet, and estimate the eruption parameters, based on our aerial surveys and on satellite images taken by the TerraSAR-X

Summary

INTRODUCTION

Lava-flow morphology reflects the emplacement and cooling dynamics of erupted lava, and is used to constrain eruption parameters, ambient conditions, and the physical properties of lavas (e.g., Huppert et al, 1982; Griffiths, 2000). Historical examples of eruptions in the sea that enable us to analyze time-series data and estimate eruption parameters are limited (e.g., Thordarson and Sigmarsson, 2009); the emplacement dynamics of lava flows in the sea are not well constrained. Since November 2013, the latest island-forming eruption comprising lava effusion and Strombolian activity has been occurring at Nishinoshima volcano, 130 km west of Chichijima, Ogasawara Islands, Japan (Fig. 1A). We describe the eruption process and the morphological evolution of the lava flows that form a new volcanic islet, and estimate the eruption parameters, based on our aerial surveys and on satellite images taken by the TerraSAR-X. The 2013 eruption began with Surtseyan-type eruptions and the formation of a cone in a shallow sea of ~20 m depth, ~400 m southeast of the existing Nishinoshima Island. The new islet was detected by TerraSAR-X on 22 November (Fig. 1B).

13 Apr 2014 JST

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