A transition from strombolian to phreatomagmatic activity induced by a lava flow damming water in a valley |
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| Institution: | 1. Institut national de la recherche scientifique (INRS), centre Eau Terre Environnement (ETE), 490 rue de la Couronne, Québec (QC), G1K 9A9, Canada;2. Geology Department, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand;3. Department of Geology and Center for Geohazards Studies, 411 Cooke Hall, University at Buffalo, Buffalo, NY 14260, USA;4. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata, 605-00143 Roma, Italy;1. Departamento de Geología, División de Ciencias de la Tierra, CICESE, PO Box 434843, San Diego, CA 92143, USA;2. Departamento de Vulcanología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Coyoacán, 04510, México, D.F, Mexico;1. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Bologna, Piazza Porta S. Donato 1, 40126 Bologna, Italy;2. Dipartimento di Scienze della Terra, Università degli Studi di Firenze, via La Pira, 4, 50121 Firenze, Italy;3. Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Sismologia e Tettonofisica, Via di Vigna Murata 605, 00143 Roma, Italy;4. CNR, IGG, sezione di Firenze, via La Pira, 4, 50121 Firenze, Italy;5. School of Earth Science, University of Bristol, Wills Memorial Building, Queen''s Road, Bristol BS8 1RJ, UK;1. Department of Geology, University at Buffalo 126 Cooke Hall, Buffalo, NY 14260, USA;2. Istituto di Geologia Ambientale e Geoingegneria (IGAG)-CNR, Roma, Italy;3. Dipartimento di Scienze della Terra, Sapienza-Università di Roma, Roma, Italy;4. Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy |
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| Abstract: | The Golan Heights is a Plio-Pleistocene volcanic plateau. Cinder cones of Late Pleistocene age are very common in the eastern and northern Golan, while phreatomagmatic deposits are relatively rare and occur just in two structures — the maar of Birket Ram and the tuff ring of Mt. Avital. The complex of Mt. Avital includes two large cinder cones, a tuff ring with an elongated central depression and several basaltic flows, some of them breach the cinder cones. The (exposed) eruptive history of the complex includes (1) an early stage of basaltic lava flows, (2) strombolian activity and the buildup of the southern cinder cone, (3) a second stage of basaltic flows and the buildup of the northern cinder cone, and then a transition to (4) phreatomagmatic explosions. The phreatomagmatic deposits include surges, lapilli fallout deposits and coarse-grained lithic tuff breccias, which were found up to 200 m above the central depression. Basaltic and scoriaceous clasts are the main component of all deposits, while juvenile material is usually a minor component, almost absent in the lapilli deposits.It is suggested that the phreatomagmatic events in Mt. Avital were induced by the infiltration of water from a lake that existed in a nearby topographic low (Quneitra Valley). The lake was formed or significantly expanded at about 300 ka due to a lava flow that blocked the drainage of the valley to the west. The interlayering of tuff and scoria at the top of the northern cinder cone and the good preservation of a lava flow top breccia under the surges imply that the phreatomagmatic activity immediately followed and even coincided with the last stages of strombolian activity. It is suggested that the dry–wet transition was triggered by the effusion of the second stage lavas and the buildup of the northern cinder cone, which probably caused a reduction of pressure in the magmatic system and allowed the lake water an access to the magmatic system. The minimum age of the phreatomagmatic events is determined by a 54 ka Musterian site which lies directly on top of the tuff in the Quneitra Valley. |
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