Orientation of the Eruption Fissures Controlled by a Shallow Magma Chamber in Miyakejima

Abstract

Orientation of the eruption fissures and composition of the lavas of the Miyakejima volcano is indicative of the competitive processes of the regional tectonic stress and the local stress generated by the activity of a magma plumbing system beneath the volcano. We examined the distributions and magmatic compositions of 23 fissures that formed within the last 2800 years, based on a field survey and a new dataset of 14 C ages. The dominant orientation of the eruption fissures in the central portion of the volcano was found to be NE-SW, which is perpendicular to the direction of regional maximum horizontal compressive stress (σ Hmax ). Magmas that show evidence of mixing between basaltic and andesitic compositions erupted mainly from the eruption fissures with a higher offset angle from the regional σ Hmax direction. The presence of a dike pattern perpendicular to the direction of maximum compression σ Hmax is an unusual and uncommon feature in volcanoes. Here we investigate the conditions possibly controlling this unexpected dike pattern. The distribution and magmatic compositions of the eruption fissures in Miyakejima volcano highlight the tectonic influence of shallow magma chamber on the development of feeder dikes in a composite volcano. The presence of a shallow dike-shaped magma chamber controls the eccentric distribution of the eruption fissures perpendicular to the present direction of σ Hmax . The injection of basaltic magma into the shallow andesitic magma chamber caused the temporal rise of internal magmatic pressure in the shallow magma chamber which elongates in NE-SW direction. Dikes extending from the andesitic magma chamber intrude along the local stress field which is generated by the internal excess pressure of the andesitic magma chamber. As the result, the eruption fissures trend parallel to the elongation direction of the shallow magma chamber. Some basaltic dikes from the deep-seated magma chamber reach the ground surface without intersection with the andesitic magma chamber. These basaltic dikes develop parallel to the regional compressive stress in NW-SE direction. The patterns of the eruption fissures can be modified in the future as was observed in the case of the destruction of the shallow magma chamber during the 2000 AD eruption.

The compositional diversity and temporal evolution of an active andesitic arc stratovolcano: Tongariro, Taupō Volcanic Zone, New Zealand

“…1: Villamor et al 2007). Additionally, the action of tectonics on regulating eruption rates and timings have inferred in many other studies elsewhere in the TVZ, the western United States, the Chilean Andes and in Japan (Lanphere and Sisson 2003;Allan et al 2012;Geshi and Oikawa 2016;Myers et al 2016;Rawson et al 2016). Interrelated behaviour between rifting and magmatism is also known in the central TVZ where rifting is aided by thermally assisted crustal weakening, and vice versa, which can result in positive feedbacks (Rowland et al 2010;Allan et al 2012;Ellis et al 2014).…”

Hydrothermal and Magmatic System of a Volcanic Island Inferred From Magnetotellurics, Seismicity, Self‐potential, and Thermal Image: An Example of Miyakejima (Japan)

“…Oyama) composed of lava and scoria. However, most events erupted outside the caldera, along fissure systems‐oriented in an SW–NE direction that is roughly perpendicular to the maximal regional compressive stress (Geshi & Oikawa, 2016). In several episodes, dikes encountered aquifers leading to phreatomagmatic eruptions (e.g., Furumio maar and Suoana‐Kazahaya maars, Figure 1c).…”

“…After ∼3 ka of repose period, volcanic activity resumed with the eruption of lava flows, scoria, and pyroclastic deposits that infilled the Kuwanokitaira caldera and formed a new stratocone (Figure 1c, brown layers). Finally, a second major collapse event generated the Hatchodaira caldera, 2 km across (Geshi & Oikawa, 2016). The post‐Hatchodaira caldera period (2.7 ka–2000 A.D.).…”

The volcanic and magmatic evolution of Tongariro volcano, New Zealand

“…≥10-100 kyr) in eruptive output and compositional variation in magmas are fundamentally influenced by tectonic processes. Episodic variations in crustal stress regimes related to volcanism have been observed (Gerst and Savage, 2004) and inferred in many studies (Lanphere and Sisson, 2003;Allan et al, 2012;Geshi and Teruki, 2016;Rawson et al, 2016;Swallow et al, 2019). Interrelated behaviour between rifting and magmatism are known in arc settings such as in the TVZ where rifting is assisted by thermally-assisted crustal weakening, and vice versa, which can result in positive feedbacks (Rowland et al, 2010;Allan et al, 2013;Ellis et al, 2014).…”