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Onshore and offshore geomorphological features of the El Golfo debris avalanche
|Autor:||Biain, Ander; Somoza, Luis; León, Ricardo; Ferrer, Mercedes; Urgeles, Roger ; Medialdea, Teresa; González Sanz, Francisco Javier; Ruano, Nuria|
|Fecha de publicación:||1-nov-2015|
|Citación:||7th International Symposium on Submarine Mass Movements and Their Consequences. Conference Abstracts: 62 (2015)|
|Resumen:||This study presents an onshore-offshore morpho-structural characterization of the El Golfo debris avalanche on El Hierro Island (Canary Archipelago, Spain) and its implications for geohazard assessment from large insular flank collapses. Erosive and depositional features have been analysed based on geological descriptions from water wells and drainage galleries excavated onshore within the El Golfo embayment, high resolution (TOPAS) and multichannel seismic reflection profiles and multibeam bathymetry and backscatter data. The observed features allow us to suggest that the event probably occurred in multiple stages. The age of these stages is a matter of discussion. The 15km wide sub-aerial extension of the headwall scarp shows a non-continuous profile formed by two semi-circular amphitheatres suggesting the presence of at least two retrogressive events. The beach levels and the possibly debris avalanche deposit identified in the drainage gallery of Los Llanillos (interbedded by post-collapse lava flows) suggest, at least, one landslide episode between the period of El Golfo volcanism. The subaerial headwall scarp extends offshore laterally bounding a smooth chute or ramp. The end of the lateral scarps at a depth of about 3000-3200m marks the transition to the distal debris avalanche depositional area. Two subunits of chaotic reflectors separated by continuous reflectors have been identified in multichannel seismic profiles indicating that the emplacement of the deposit took place in at least two major stages separated by an unknown period of time. Within the smooth ramp, depositional features have been identified with multibeam and high resolution seismic data. We correlate these features with minor, recent gravitational instabilities of the infralitoral sedimentary wedge. The data presented shows that lateral collapse of oceanic volcanoes is less catastrophic than previously thought. It also shows that the associated hazard and the tsunamigenic potential in particular should be readily reassessed|
|Descripción:||7th International Symposium on Submarine Mass Movements and Their Consequences, 1-4 November 2015, Wellington, New Zealand|
|Aparece en las colecciones:||(ICM) Comunicaciones congresos|
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