Volcanic, tectonic and mass-wasting processes offshore Terceira Island (Azores) revealed by high-resolution seafloor mapping

Abstract

Terceira Island, in the Azores Archipelago, lies at the intersection of four submarine volcanic ridges. New highresolution bathymetric and seismic reflection data have been used to analyze the main volcanic, tectonic and mass-wasting features of the island offshore. Volcanic features such as linear volcanic centers, and pointy and flat-topped cones are mainly concentrated on the narrow western and north-western ridges, characterized by an overall rugged morphology. Fault scarps dominate mainly the broad eastern and south-eastern ridges, which are characterized by an overall smooth and terrace-like morphology. On the eastern ridge, faults form a series of horsts and grabens related to the onshore Lajes Graben. The strikes of the fault scarps, linear volcanic centers and align-ment of volcanic cones on the ridges reveal two main structural trends, WNW-ESE and NNW-SSE, consistent with the main tectonic structures observed on the Azores Plateau. In contrast, a large variability of strike was observed in interridge areas, reflecting the relative importance of regional and local stresses in producing these structures. Masswasting features are subordinate and mostly represented by hundred meter-wide scars that indent the edge of the insular shelf surrounding the island, apart from two large, deeper scars identified on the southern steep flank of the western ridge. Finally, the remarkable morphostructural differences between the western and eastern ridges are discussed in the framework of the evolution Editorial responsibility: A. Gudmundsson

Progressive Changes in Magma Transport at the Active Serreta Ridge, Azores

“…Serreta Ridge has an along axis length of ~25 km and extends from the Santa Bárbara volcano in WNW direction. The NW Terceira Ridge has a NW‐SE orientation with elongated eruptive centers striking in ~140° direction (Casalbore et al, ), in contrast to those from Serreta Ridge striking ~120°. Smaller volcanic ridges with elongated volcanic centers forming SR‐B and SR‐C of the N' Serreta Ridges (Figure ) are located between the Serreta and Northwest Terceira Ridges.…”

“…Structures located subaerially in the extension of the Serreta Ridge form the most pronounced subaerial volcano‐tectonic structures in the western part of Terceira. Alignments of volcanic cones ESE of the Santa Bárbara caldera are oriented between 110 and 120° strike (Pimentel et al, ), equivalent to similarly oriented structures WNW of Santa Bárbara (Madeira et al, ), and Serreta Ridge (Casalbore et al, ). The area in which subaerial and submarine volcano‐tectonic structures are predominantly oriented WNW‐ESE is therefore summarized as Santa Bárbara Rift.…”

“…Location and orientation of the NW Terceira Ridge is from Quartau et al (). (c) Simplified map of Terceira and surrounding seafloor with volcano‐tectonic structures modified after Navarro et al (); Nunes et al (); Quartau et al (); Casalbore et al (); and Madeira et al (). Light grey area highlights submarine areas with less than 500 m water depth.…”

Late Quaternary paleo sea level geomorphological markers of opposite vertical movements at Salina volcanic island (Aeolian Arc)

“…Additionally, the depth of the shelf edge can be strongly influenced by other processes, such as subsequent volcanic progradation (Quartau et al, ) and/or emplacement of volcaniclastic sediments (Quartau et al, ; Casalbore et al, ; Romagnoli et al, ), as well as by retrogressive erosion related to canyon heads or slide scars that commonly indent the shelf (Quartau et al, ; Romagnoli et al, , ; Casalbore et al, ; Chiocci and Casalbore, ). These processes typically cause an upward and/or landward shift of the shelf edge, resulting in depths up to tens of metres shallower than the originally formed one.…”

Submarine Depositional Terraces at Salina Island (Southern Tyrrhenian Sea) and Implications on the Late-Quaternary Evolution of the Insular Shelf

“…In the last few decades, recent advances in seafloor imagery systems enabled to extensively map the submarine flanks of volcanic islands in different geodynamic setting, revealing a large variability of landforms due to volcanic, tectonic, and erosive-depositional processes [1][2][3][4][5][6][7][8]. Until now, most of these studies focused on large-scale instability processes affecting volcanic flanks, mainly in relation to their associated tsunamigenic potential and geohazard assessment [9][10][11][12].…”