Dynamics of deep submarine silicic explosive eruptions in the Kermadec arc, as reflected in pumice vesicularity textures
Dynamics of deep submarine silicic explosive eruptions in the Kermadec arc, as reflected in pumice vesicularity textures
Despite increasing recognition of silicic pumice-bearing deposits in the deep marine environment, the processes involved in explosive silicic submarine eruptions remain in question. Here we present data on bubble sizes and number densities (number of bubbles per unit of melt matrix) for deep submarine-erupted pumices from three volcanoes (Healy, Raoul SW and Havre) along the Kermadec arc (SW Pacific) to investigate the effects of a significant (>~1 km) overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation. We compare these textural data with those from chemically similar, subaerially erupted pyroclasts from nearby Raoul volcano as well as submarine-erupted ‘Tangaroan’ fragments derived by non-explosive, buoyant detachment of foaming magma from Macauley volcano, also along the Kermadec arc. Deep submarine-erupted pumices are macroscopically similar (colour, density, texture) to subaerial or shallow submarine-erupted pumices, but show contrasting microscopic bubble textures. Deep submarine-erupted pyroclasts have fewer small (<10 ?m diameter) bubbles and narrower bubble size distributions (BSDs) when compared to subaerially erupted pyroclasts from Raoul (35-55 ?m vs. 20-70 ?m range in volume based median bubble size, respectively). Bubble number density (BND) values are consistently lower than subaerial-erupted pyroclasts and do not display the same trends of decreasing BND with increasing vesicularity. We interpret these textural differences to result from deep submarine eruptions entering the water column at higher pressures than subaerial eruptions entering the atmosphere (~10 MPa vs. 0.1 MPa for a vent at 1000 mbsl). The presence of an overlying water column acts to suppress rapid acceleration of magma, as occurs in the upper conduit of subaerial eruptions, therefore suppressing coalescence, permeability development and gas loss, amounting to closed-system degassing conditions. The higher confining pressure environment of deep submarine settings hinders extensive post-fragmentation clast expansion, coalescence of bubbles, and thinning of bubble walls, causing clasts to have similar BND values regardless of their vesicularity. Although deep submarine-erupted pyroclasts are closely similar to their subaerial counterparts on the basis of bulk vesicularities and macroscopic appearance, they differ markedly in their microscopic textures, allowing them to be fingerprinted in modern and ancient pumiceous marine sediments.
Pumice, Submarine volcanism, Bubble number density, Kermadec arc
314-332
Rotella, Melissa D.
be18845a-aaf1-4f05-ae92-55447b6774e8
Wilson, Colin J.N.
5953011a-09ee-47de-a41d-b1e81eaf1037
Barker, Simon J.
27644ab9-faf3-4043-ab4a-9220f23196f7
Schipper, C. Ian
da647c0b-b982-4cf5-8503-cf5386639264
Wright, Ian C.
be2a8931-3932-4f1e-b387-43e3652bf3fc
Wysoczanski, Richard J.
92f8ff48-fc8e-4354-abca-be150a617b9e
15 August 2015
Rotella, Melissa D.
be18845a-aaf1-4f05-ae92-55447b6774e8
Wilson, Colin J.N.
5953011a-09ee-47de-a41d-b1e81eaf1037
Barker, Simon J.
27644ab9-faf3-4043-ab4a-9220f23196f7
Schipper, C. Ian
da647c0b-b982-4cf5-8503-cf5386639264
Wright, Ian C.
be2a8931-3932-4f1e-b387-43e3652bf3fc
Wysoczanski, Richard J.
92f8ff48-fc8e-4354-abca-be150a617b9e
Rotella, Melissa D., Wilson, Colin J.N., Barker, Simon J., Schipper, C. Ian, Wright, Ian C. and Wysoczanski, Richard J.
(2015)
Dynamics of deep submarine silicic explosive eruptions in the Kermadec arc, as reflected in pumice vesicularity textures.
Journal of Volcanology and Geothermal Research, 301, .
(doi:10.1016/j.jvolgeores.2015.05.021).
Abstract
Despite increasing recognition of silicic pumice-bearing deposits in the deep marine environment, the processes involved in explosive silicic submarine eruptions remain in question. Here we present data on bubble sizes and number densities (number of bubbles per unit of melt matrix) for deep submarine-erupted pumices from three volcanoes (Healy, Raoul SW and Havre) along the Kermadec arc (SW Pacific) to investigate the effects of a significant (>~1 km) overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation. We compare these textural data with those from chemically similar, subaerially erupted pyroclasts from nearby Raoul volcano as well as submarine-erupted ‘Tangaroan’ fragments derived by non-explosive, buoyant detachment of foaming magma from Macauley volcano, also along the Kermadec arc. Deep submarine-erupted pumices are macroscopically similar (colour, density, texture) to subaerial or shallow submarine-erupted pumices, but show contrasting microscopic bubble textures. Deep submarine-erupted pyroclasts have fewer small (<10 ?m diameter) bubbles and narrower bubble size distributions (BSDs) when compared to subaerially erupted pyroclasts from Raoul (35-55 ?m vs. 20-70 ?m range in volume based median bubble size, respectively). Bubble number density (BND) values are consistently lower than subaerial-erupted pyroclasts and do not display the same trends of decreasing BND with increasing vesicularity. We interpret these textural differences to result from deep submarine eruptions entering the water column at higher pressures than subaerial eruptions entering the atmosphere (~10 MPa vs. 0.1 MPa for a vent at 1000 mbsl). The presence of an overlying water column acts to suppress rapid acceleration of magma, as occurs in the upper conduit of subaerial eruptions, therefore suppressing coalescence, permeability development and gas loss, amounting to closed-system degassing conditions. The higher confining pressure environment of deep submarine settings hinders extensive post-fragmentation clast expansion, coalescence of bubbles, and thinning of bubble walls, causing clasts to have similar BND values regardless of their vesicularity. Although deep submarine-erupted pyroclasts are closely similar to their subaerial counterparts on the basis of bulk vesicularities and macroscopic appearance, they differ markedly in their microscopic textures, allowing them to be fingerprinted in modern and ancient pumiceous marine sediments.
Text
Rotella et al 2015.pdf
- Accepted Manuscript
More information
Accepted/In Press date: June 2015
Published date: 15 August 2015
Keywords:
Pumice, Submarine volcanism, Bubble number density, Kermadec arc
Organisations:
Marine Geoscience
Identifiers
Local EPrints ID: 377946
URI: http://eprints.soton.ac.uk/id/eprint/377946
ISSN: 0377-0273
PURE UUID: a8ba894e-0680-4401-8ba4-317001912e0c
Catalogue record
Date deposited: 11 Jun 2015 09:16
Last modified: 15 Mar 2024 05:17
Export record
Altmetrics
Contributors
Author:
Melissa D. Rotella
Author:
Colin J.N. Wilson
Author:
Simon J. Barker
Author:
C. Ian Schipper
Author:
Ian C. Wright
Author:
Richard J. Wysoczanski
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics