Magma intrusion and discharge process at the initial stage of the 2000 activity of Miyakejima, Central Japan, inferred from tilt and GPS data

Abstract

SUMMARY The 2000 eruptive activity of Miyakejima island began with an earthquake swarm and crustal deformation that was clearly observed by continuous observations of ground tilt and GPS on Miyakejima. Based on the crustal deformation data, we estimated the magma migration process at the initial stage (18:30 LT on 2000 June 26—06:00 LT on 2000 June 27) of the activity. The activity in 2000 has been characterized by a collapse‐caldera formation and no fissure eruption on the flank of the island, which is markedly different from the style of the recent eruptions in 1940, 1962 and 1983. We constructed a source model that approximately explains the crustal deformation data. The model consists of four dykes, of which three are intruding dykes and the other is a contracting dyke. We can infer the magma migration process at the initial stage from the model as follows. At 18:30 LT on June 26, the magma began to ascend from a dyke‐shaped magma chamber and intrude at the southwestern flank of Miyakejima. In the intrusion, the total volume of intruded magma was ∼4 × 106 m3. At around 21:00 LT, a relatively large volume of magma began to intrude as a dyke beneath the west coast of Miyakejima. The dyke then propagated laterally towards the northwest. The amount of magma intruded from 21:00 LT to 01:00 LT was ∼40 × 106 m3. This large intrusion caused a discharge of magma from the magma chamber. The northwestward propagation of the dyke and the contraction of the chamber continued thereafter. The discharge of magma from the chamber beneath Miyakejima probably starved the first intrusion that had been ascending towards the southwestern flank of the island, resulting in the collapse‐caldera formation after the initial stage. The style of the 2000 eruptive activity relative to recent activity has primarily been changed by the subsurface discharge of magma towards the northwest.

Volume change of the magma reservoir relating to the 2011 Kirishima Shinmoe-dake eruption—Charging, discharging and recharging process inferred from GPS measurements

“…The real magma reservoir is not an infinitesimal sphere, and the crust has heterogeneous and layered structures. Many previous studies have tried to model ground deformation by using a complex source geometry (e.g., Hashimoto and Tada, 1988;Segall et al, 2001;Ueda et al, 2005), or heterogeneous crustal structures (e.g., De Natale and Pingue, 1993;Fernandez and Rundle, 1994;Trasatti et al, 2003). We acknowledge that the models used in this study are too simple to represent real phenomena, the limited station distribution does not allow us to introduce a complex source model or heterogeneous crustal structure.…”

Earthquake swarms preceding the 2000 eruption of Miyakejima volcano, Japan

“…Magma intrusion beneath Miyakejima has also been studied using Kinematic GPS (Irwan et al 2003) and tilt and GPS data (Ueda et al 2004). Both postulate several dykes located southwest of Miyakejima to account for the observed GPS and/or tilt data.…”

Banded tremor at Miyakejima volcano, Japan: Implication for two‐phase flow instability

“…[2] The eruption of Miyakejima volcano, Japan, began on 26 June, 2000, with a subsurface dike intrusion [Ueda et al, 2005]. One of the most characteristic activities of this eruption was the formation of a caldera from July to August 2000 [e.g., Fujita et al, 2004;Geshi et al, 2002].…”