Description: Seismic, sidescan sonar, bathymetric multibeam and ODP (Ocean Drilling Program) data obtained in the submarine channel between the volcanic islands of Gran Canaria and Tenerife allow to identify constructive features and destructive events during the evolution of both islands. The most prominent constructive features are the submarine island flanks being the acoustic basement of the seismic images. The build-up of Tenerife started following the submarine stage of Gran Canaria because the submarine island flank of Tenerife onlaps the steeper flank of Gran Canaria. The overlying sediments in the channel between Gran Canaria and Tenerife are chaotic, consisting of slumps, debris flow deposits, syn-ignimbrite turbidites, ash layers, and other volcaniclastic rocks generated by eruptions, erosion, and flank collapse of the volcanoes. Volcanic cones on the submarine island flanks reflect ongoing submarine volcanic activity. The construction of the islands is interrupted by large destructive events, especially by flank collapses resulting in giant landslides. Several Miocene flank collapses (e.g., the formation of the Horgazales basin) were identified by combining seismic and drilling data whereas young giant landslides (e.g., the Güimar debris avalanche) are documented by sidescan, bathymetric and drilling data. Sediments are also transported through numerous submarine canyons from the islands into the volcaniclastic apron. Seismic profiles across the channel do not show a major offset of reflectors. The existence of a repeatedly postulated major NE–SW-trending fault zone between Gran Canaria and Tenerife is thus in doubt. The sporadic earthquake activity in this area may be related to the regional stress field or the submarine volcanic activity in this area. Seismic reflectors cannot be correlated through the channel between the sedimentary basins north and south of Gran Canaria because the channel acts as sediment barrier. The sedimentary basins to the north and south evolved differently following the submarine growth of Gran Canaria and Tenerife in the Miocene.

Description: Seismic P-wave travel times collected during METEOR cruise M24 are inverted to derive a three-dimensional model of the P-wave velocity structure of the northern part of Gran Canaria, Canary Islands. The data consist of 6689 P-wave travel times from 1487 offshore air-gun shots which were recorded by both land-based seismometers and ocean bottom hydrophones. The crustal structure is well imaged by the data set as demonstrated by analysis of the resolution and tests with synthetic data. The volcanic island is characterized by generally high P-wave velocities (〉5.5 km/s) and a heterogeneous structure with large lateral velocity variations. High P-wave velocities are found around the centers of the Miocene shield volcanoes in the vicinity of Agüimes, San Nicolas, and Agaete as well as the center of the Pliocene Roque Nublo volcano. The velocity structure suggests a high percentage of dense intrusive rocks. Some of the intrusive rocks were emplaced during the eruption of 〉1000 km3 of Miocene felsic magmas following the basaltic shield phase. The velocity structure beneath La Isleta peninsula and its submarine continuation is interpreted as a volcanic rift zone with abundant dikes. The velocities decrease to 〈5 km/s north of the coastline. A high velocity zone thinning away from the central edifice is interpreted as the massive island flank extending up to 50 km off the coast which is underlain by prevolcanic Neogene–Jurassic sediments. The igneous part of the oceanic crust exhibits an anomalous structure with a relatively small thickness (∼3 km) layer 3 and a 2–4-km-thick layer 2, probably reflecting a modification of the crust due to long-lasting magmatic intrusive activity during the evolution of the Canary Islands. The Moho north of Gran Canaria is found at a depth of ∼15 km. The structure of Gran Canaria and the adjacent ocean basin is thought to be the result of a diffuse mantle upwelling under a slowly moving plate.

Description: The morphology and structure of the submarine flanks of the Canary Islands were mapped using the GLORIA long-range side-scan sonar system, bathymetric multibeam systems, and sediment echosounders. Twelve young (〈2 Ma) giant landslides have been identified on the submarine flanks of the Canary Islands up to now. Older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the Canary Islands. Most slides were found on the flanks of the youngest and most active islands of La Palma, El Hierro, and Tenerife, but young giant landslides were also identified on the flanks of the older (15–20 Ma) but still active eastern islands. Large-scale mass wasting is an important process during all periods of major magmatic activity. The long-lived volcanic constructive history of the islands of the Canary Archipelago is balanced by a correspondingly long history of destruction, resulting in a higher landslide frequency for the Canary Islands compared to the Hawaiian Islands, where giant landslides only occur late in the period of active shield growth. The lower stability of the flanks of the Canaries is probably due to the much steeper slopes of the islands, a result of the abundance of highly evolved intrusive and extrusive rocks. Another reason for the enhanced slope instability is the abundance of pyroclastic deposits on Canary Islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas. Dike-induced rifting is most likely the main trigger mechanism for destabilization of the flanks. Flank collapses are a major geological hazard for the Canary Islands due to the sector collapses themselves as well as triggering of tsunamis. In at least one case, a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse.

Description: The Canary Archipelago, located off the West African continental margin, is one of the largest oceanic island groups in the ocean basins (Fig. 1). A general but slightly diffuse westward age progression of the shield phases of the islands was interpreted as evidence for a hot spot origin of the Canary Islands (Wilson 1973; Schmincke 1982; Carracedo et al. 1998). During the last 15 years, morphological studies of the submarine flanks of ocean islands with swath bathymetry, sidescan sonar and high-resolution seismic systems have demonstrated that giant submarine landslides play an important role during the evolut ion of volcanic islands. Landslides on ocean islands are one of the most important transport processes of volcaniclastic material into the volcanic apron. They are a major geological hazard due to the sector collapses themselves as weil as triggering of tsunamis.

Description: The Sorokin Trough (Black Sea) is characterized by diapiric structures formed in a compressional tectonic regime that facilitate fluid migration to the seafloor. We present acoustic data in order to image details of mud volcanoes associated with the diapirs. Three types of mud volcanoes were distinguished: cone-shaped, flat-topped, and collapsed structures. All mud volcanoes, except for the Kazakov mud volcano, are located above shallow mud diapirs and diapiric ridges. Beyond the known near-surface occurrence of gas hydrates, bottom simulating reflectors are not seen on our seismic records, but pronounced lateral amplitude variations and bright spots may indicate the presence of gas hydrates and free gas.