Banco D. João de Castro

The boat runs two hours out of Praia da Vitória before the crater rim rises out of open water at a well-agreed 12 to 13 metres. Descend the line straight onto it: gas bubbles up through an extensive fumarole field, the visible signature of a volcano that is still active underneath you. The rim drops away into the old caldera, floor around 25 metres, with two smaller parasitic craters folded into the north-west flank. A second summit, reported near 40 metres further inside and rarely dived, sits below the rim, and the seamount's confirmed working depth runs to 60 metres for those equipped for it. Because there is no reef or wall to shelter behind, the current across the rim and caldera runs moderate to strong, and the line is not optional: guides expect divers to stay clipped to it and release only on their say. What draws the crossing is what shows up in open water around the structure: sicklefin devil rays, sold to divers as manta rays, hold station over the seamount, with yellowmouth barracuda, Atlantic bonito, Bermuda chub and amberjack working the same water column. Loggerhead turtles turn up occasionally. The ambient water sits at 18 to 24°C; the vents themselves run far hotter, 39 to 83°C at the openings, a detail worth remembering before anyone is tempted to reach in.

The bank takes its name from the Portuguese hydrographic survey ship NH D. João de Castro, which identified and catalogued it on 28 July 1941. Its more dramatic history is older: on 31 December 1720 a Surtseyan eruption raised the crater above the waves entirely, briefly forming a new island, Ilha Nova, about 1.5 kilometres long and 250 metres high, popularly remembered as briefly the Azores' tenth island. How long it lasted is not settled. One registry-style account has it eroding away by July 1722, close to nineteen months after it rose; the University of the Azores' CE3C research page puts the same erosion at around four months.1 Minor seismic activity was recorded again in 1997 and 2012, tremors up to Mercalli III/IV. None of it registers as an active hazard for a diver today: it belongs to the seamount's geological record, well outside anything a diver needs to plan around.

Banco Dom João de Castro is an offshore seamount dive, not an island-coast one: a two-hour crossing to a live volcano, its crater rim close enough to touch and its hydrothermal vents plainly visible. A Graciosa-based operator also ran an expedition to the bank in 2011, a sign that more than one island's operators claim it as their own offshore objective. Reaching it takes booking weeks ahead, clearing the certification floor, and committing a full day at sea.

The standard trip fills a full eight-hour day from Praia da Vitória: departing early morning, two dives with a surface interval between them, groups kept to four to six divers, minimum age 16, priced around EUR 250 per person. Advanced Open Water and 50 logged dives is the booking floor, with active-diver status and medical clearance for any pre-existing condition also required; a refresher is worth arranging if you have been out of the water a while, since there is no learning curve built into this trip. The current is the reason for the descent line, and the remoteness, roughly two hours from the nearest shelter, is the tourism board's own stated reason the site is kept for experienced divers only. This is a daylight trip: both dives run inside the same eight-hour window, out and back in one day.