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Changing eruptive styles and textural features from phreatomagmatic to strombolian activity of basaltic littoral cones: Los Erales cinder cone, Tenerife, Canary Islands


Title (Dublin Core)

Changing eruptive styles and textural features from phreatomagmatic to strombolian activity of basaltic littoral cones: Los Erales cinder cone, Tenerife, Canary Islands

Description (Dublin Core)

Monta&ntilde;a Los Erales is a 70 m high Quaternary cinder cone in the Bandas del Sur region, south Tenerife. Field observations on excavated sections and SEM analysis of tephra samples from the cone suggest that the eruption style of this vent changed progressively from an initial hydrovolcanic phase, through a transitional stage, to one that was entirely strombolian. Clast sizes increase from &le;&#239;&#128;&#160;1 cm angular lapilli in hydrovolcanic samples to 15 cm bombs in strombolian samples. Vesicles also increase in size from 0.5 mm to 1.2 mm, becoming more rounded in the strombolian samples. Palagonitization, extensive in the hydrovolcanic deposits, becomes less noticeable in strombolian deposits.<br /> To investigate the causes for and the nature of these changes in eruptive style, products from each major unit were analysed for their morphology, using scanning electron microscopy with both SE and BSE imaging as tephra morphologies are known to reflect the eruptive regime and degree of explosivity at the time of eruption. SEM imaging of hydrovolcanic samples illustrate angular fragments that have been rapidly quenched and contain high levels of palagonitisation and zeolitisation, whereas strombolian samples appear to be less altered and display larger clast sizes and vesicles. Our results confirm that the initial phase of activity was largely driven by magma-water (coolant) interaction, where magma may have interacted with a lens of fresh ground or surface water, causing intense fragmentation of the magma. With proceeding eruptive activity the water became exhausted, giving rise to an entirely strombolian eruptive style. Additionally, fossil diatoms were found in hydrovolcanic samples, further emphasising the influence of a, probably fluvial, water source during the early phase of emplacement.<br><br>La Monta&ntilde;a de Los Erales es un cono de c&iacute;nder del Cuaternario de 70 m de altura situado en la zona de las Bandas del Sur, en el litoral meridional de la isla de Tenerife. Observaciones de campo en secciones excavadas en los flancos del cono y an&aacute;lisis SEM de las muestras de tefra sugieren que el estilo eruptivo de este aparato volc&aacute;nico cambi&oacute; progresivamente durante la erupci&oacute;n de una fase inicial hidrovolc&aacute;nica a una final enteramente estromboliana, con estadios intermedios transicionales. El tama&ntilde;o de los clastos aumenta de &le;&#239;&#128;&#160;1 cm de lapilli angular en las muestras hidrovolc&aacute;nicas a bombas de 15 cm en las estrombolianas. Las ves&iacute;culas tambi&eacute;n aumentan en tama&ntilde;o desde 0,5 mm a 1,2 mm, volvi&eacute;ndose m&aacute;s redondeadas en las muestras estrombolianas. Los intensos procesos de palagonitizaci&oacute;n de los dep&oacute;sitos hidrovolc&aacute;nicos son menos significativos en las fases estrombolianas.<br /> Con objeto de investigar la naturaleza y las causas de estos cambios se analiz&oacute; la morfolog&iacute;a de los productos de las principales fases. Se han utilizado para ello im&aacute;genes de microscop&iacute;a electr&oacute;nica (SE y BSE), ya que se sabe que las diferentes morfolog&iacute;as de estos piroclastos reflejan el r&eacute;gimen eruptivo y el grado de explosividad durante la erupci&oacute;n. Las im&aacute;genes SEM de las muestras hidrovolc&aacute;nicas presentan fragmentos angulares que se han enfriado r&aacute;pidamente y con elevado grado de palagonitizaci&oacute;n y zeolitizaci&oacute;n. Las estrombolianas, en cambio, aparecen menos alteradas y muestran mayor tama&ntilde;o de clastos y ves&iacute;culas.<br /> Los resultados obtenidos indican que la fase inicial de la erupci&oacute;n se caracteriza por una importante interacci&oacute;n magma-agua (refrigerante), probablemente relacionada con una cantidad limitada de agua superficial o fre&aacute;tica que produjo la intensa fragmentaci&oacute;n del magma. En el transcurso de la erupci&oacute;n la fuente de agua se agot&oacute;, dando lugar a las fases finales de car&aacute;cter enteramente estromboliano. F&oacute;siles de diatomeas, que se han encontrado asociados a las muestras hidrovolc&aacute;nicas, refuerzan la posibilidad de que el agua fuera de origen superficial, probablemente el cauce de un barranco.

Creator (Dublin Core)

Gould, R.
Byrne, K.
Carracedo, J. C.
Troll, V. R.
Clarke, H.

Subject (Dublin Core)

phreatomagmatic eruptions
cinder cones
Los Erales
erupciones freatomagm&#225;ticas
conos de c&#237;nder

Publisher (Dublin Core)

Consejo Superior de Investigaciones Científicas

Date (Dublin Core)


Type (Dublin Core)


Identifier (Dublin Core)


Source (Dublin Core)

Estudios Geologicos, Vol 61, Iss 3-6, Pp 121-134 (2005)

Language (Dublin Core)


Relation (Dublin Core)

Provenance (Dublin Core)

Journal Licence: CC BY