NDLI: On the conditions of sheet injections and eruptions in stratovolcanoes

Content Provider	Springer Nature Link
Author	Gudmundsson, Agust Brenner, Sonja L.
Copyright Year	2005
Abstract	Nearly all eruptions in stratovolcanoes (composite volcanoes, central volcanoes) are supplied with magma through fractures. Consequently, a primary physical condition for an eruption to occur in a stratovolcano is that a magma-driven fracture is able to propagate to the surface. Magma-filled fractures, frozen or fluid, are referred to as sheet intrusions. More specifically, they are named dykes when subvertical, and inclined (or cone) sheets when inclined. Field observations indicate that most sheet intrusions do not reach the surface to feed eruptions but rather become arrested at various crustal depths. For this reason periods of volcanic unrest with sheet injections are much more common than volcanic eruptions. Whether a sheet intrusion becomes arrested or, alternatively, propagates to the surface depends primarily on the stress field in the stratovolcano. A stratovolcano normally consists of layers of contrasting mechanical properties, such as soft (low Young’s modulus) pyroclastic units and stiff (high Young’s modulus) lava flows. We present numerical models indicating that volcanoes composed of such layers commonly develop stress fields encouraging sheet and dyke arrest. The models indicate that a necessary condition for a sheet intrusion to reach the surface and feed a volcanic eruption is that the stress field along the sheet pathway becomes homogenised. We propose that much of the activity in a stratovolcano during a volcanic cycle encourages stress-field homogenisation. Field studies show that the sheet intrusions in individual stratovolcanoes have various dips: some are vertical dykes, others inclined sheets, and still others horizontal sills. Analytical models indicate that the dip of a sheet reaching the surface can have great effects on the magma transport during an eruption. This effect is normally greater for a flat volcano such as a collapse caldera than for a stratovolcano that forms a topographic high. We conclude that the shallower the dip of a sheet intrusion, the less will be its volumetric magma transport to the surface of a stratovolcano.
Starting Page	768
Ending Page	782
Page Count	15
File Format	PDF
ISSN	02588900
Journal	Bulletin of Volcanology
Volume Number	67
Issue Number	8
e-ISSN	14320819
Language	English
Publisher	Springer-Verlag
Publisher Date	2005-07-01
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Volcanic eruption Sheet arrest Crustal layering Crustal stress Magma transport Stratovolcano
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology

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