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The Mid-Cayman spreading centre is an ultraslow-spreading ridge in the Caribbean Sea. Its extreme depth and geographic isolation from other mid-ocean ridges offer insights into the effects of pressure on hydrothermal venting, and the biogeography of vent fauna. Here we report the discovery of two hydrothermal vent fields on the Mid-Cayman spreading centre. The Von Damm Vent Field is located on the upper slopes of an oceanic core complex at a depth of 2,300 m. High-temperature venting in this off-axis setting suggests that the global incidence of vent fields may be underestimated. At a depth of 4,960 m on the Mid-Cayman spreading centre axis, the Beebe Vent Field emits copper-enriched fluids and a buoyant plume that rises 1,100 m, consistent with >400 °C venting from the world's deepest known hydrothermal system. At both sites, a new morphospecies of alvinocaridid shrimp dominates faunal assemblages, which exhibit similarities to those of Mid-Atlantic vents.

Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.

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Abstract. 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, E1 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 co•rrespondingly 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.

Large‐scale landslides occur on the flanks of many volcanic oceanic islands worldwide. None have taken place in historical time, but their geohazard potential, especially their ability to generate tsunamis, is large. The Cape Verde Islands are a group of 10 large and several smaller volcanic islands off the coast of West Africa between 15 and 17°N. A single flank landslide has previously been described from the island of Fogo, but systematic analysis of the Cape Verde group has until now been lacking. This paper describes and interprets a multibeam bathymetry data set covering the slopes of the western Cape Verde Islands, including those of the islands with the most recent volcanic activity, Fogo in the southwest, and Santo Antao in the northwest. All of the larger islands show evidence of large flank landslides, although only Fogo and the southwest part of Santo Antao have failed in the last 400 ka. Tope de Coroa, the volcano at the southwest end of Santo Antao, has been inactive for the past 170 ka and is judged to have a low landslide potential unless volcanic activity resumes. In contrast, there would seem to be a high probability of a future east directed landslide on Fogo, from the area of the highly active Pico do Fogo volcano, although it is impossible to predict a timescale for such an event. A tsunami generated by such a landslide could have a catastrophic effect on the adjacent island of Santiago and possibly even farther afield on the West African coast.

The coastal waters of the Maltese Islands, central Mediterranean Sea, sustain a diversity of marine habitats and support a wide range of human activities. The islands' shallow waters are characterised by a paucity of hydrographic and marine geo-environmental data, which is problematic in view of the requirements of the Maltese Islands to assess the state of their coastal waters by 2011 as part of the EU Marine Strategy Directive. Multibeam echosounder (MBES) systems are today recognised as one of the most effective tools to map the seafloor, although the quantitative characterisation of MBES data for seafloor and habitat mapping is still an underdeveloped field. The purpose of this *Manuscript Click here to download Manuscript: Manuscript.doc Click here to view linked References 2 study is to outline a semi-automated, Geographic Information System-based methodology to map the distribution of seafloor composition and morphology in shallow coastal waters using high-resolution MBES data. We test this methodology in a 28 km 2 area of Maltese coastal waters. Three data sets were collected from this study area: (i) MBES bathymetry and backscatter data; (ii) Remotely Operated Vehicle imagery and (iii) photographs and sediment samples from dive surveys. Our approach combines a suite of topographic and textural analytical techniques to map different types of seafloor morphologies and compositions at various scales. Topographic analyses, based on bathymetric data, classify the seabed into five morphological zones and features-flat and sloping areas, crests, depressions and breaks of slope-by using morphometric attributes, the Bathymetric Position Index and geomorphometric mapping. Textural analyses of backscatter and bathymetry data segment the seafloor into four classes-medium sand, maerl associated with sand and gravel, seagrass settled on sand and gravel, and seagrass settled on bedrock-using roughness estimation, TexAn analyses and supervised classification based on information from training stations. The resulting topographic and seabed composition maps were combined to plot the distribution of the predominant habitats in the coastal waters offshore the NE Malta, some of which are of high conservation value. Groundtruthing of the habitat map using ROV imagery and dive observations confirms that our approach produces a simplified and accurate representation of seafloor habitats in a quick and objective manner while using all the information available within MBES data sets.