The morphology of insular shelves as a key for understanding the geological evolution of volcanic islands: Insights from Terceira Island (Azores)

Abstract

Shelves from volcanic ocean islands result from the competition between two main processes, wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension. In places where erosion dominates over volcanism, shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved. In this study, new multibeam bathymetry and high-resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of Terceira Island in order to improve the understanding of its evolution. Subaerial morphological and geological/stratigraphic data were also used to establish the connection between the onshore and offshore evolution. Shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island; most of the older edifices have wider shelves than younger ones. The shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view. Its depth was also used to reconstruct vertical movements, showing that older edifices like Serra do Cume-Ribeirinha, Guilherme Moniz, and Pico Alto have subsided while more recent ones have not. The morphology of the shelf (namely the absence/ presence of fresh lava flow morphologies and several types of erosional, depositional, and tectonic features) integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution.

Episodic, rapid sea-level rises on the central Mediterranean shelves after the Last Glacial Maximum: A review

“…In particular, the infralittoral prograding wedges (IPW; Hernández-Molina et al, 2000), also called submerged depositional terraces (SDTs; Massari and Chiocci, 2006), are seawardprograding sedimentary wedges formed below storm wave base on the WRS, inferred to have accumulated from downwelling storm currents (Hernández-Molina et al, 2000). These features trend parallel to the shore, show a backstepping pattern and commonly occur on narrow and steep shelves, such as on segments of tectonically-controlled continental margins and on the flanks of insular volcanoes (Hernández-Molina et al, 2000;Massari and Chiocci, 2006;Casalbore et al, 2010;Romagnoli et al, 2013a;Quartau et al, 2014). Following Hernández-Molina et al (1994), the IPWs probably accumulated during phases of relative sea-level still-stand or slow rise punctuating the post-LGM transgression.…”

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

“…In detail, the near-shore terrace is very similar in size and depth of its edge to present-day examples of prograding wedges observed on others insular shelves along the Mediterranean area, such as in the other Aeolian Islands [22] and the Pontine Archipelago [18,30] as well as along tectonically-controlled continental margins of Southern Iberia (infralittoral prograding wedge, [31]) and Southern Italy [32]. The depth range (10-25 m) of these edges is, in fact, compatible with the estimated present-day, local storm-wave base level in the central and western Mediterranean [20,21,33], whereas it is markedly lower with respect to the edge of similar features observed around oceanic islands, where the storm-base level is deeper [13,14,23]. Based on such evidences and considering that the present-day level has been attained since ca.…”

“…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]. Only in the last years, some papers paid attention to the shallow-water areas around volcanic islands, where the morphological characteristics of the shelf (i.e., shelf width and depth of its edge) can be used: (a) to reconstruct the original extension of early volcanic centres in the development of the island, including deeply eroded submarine cones, with respect to subaerial main centres, and (b) to assess the vertical movements of the volcanic edifice that have occurred after the shelf formation due to erosion [13][14][15][16][17]. Regarding this, another geomorphological/stratigraphic marker for relative paleo-sea level reconstruction and assessment of vertical movement is the edge depth of prograding sedimentary wedges, forming morphological terraces (Submarine Depositional Terraces, SDT hereafter, [18][19][20]).…”

The multimethod palaeointensity approach applied to volcanics from Terceira: full-vector geomagnetic data for the past 50 kyr

“…1, e.g. Self 1976;Calvert et al 2006;Gertisser et al 2010;Quartau et al 2014;Zanon & Pimentel 2015). The oldest volcano of Terceira is Cinco Picos (>401 ka; Hildenbrand et al 2014) that together with Guilherme 592 L.V.…”