Banco D. João de Castro: exploring where the Earth breathes under the sea

Offshore, between the islands of Terceira and São Miguel, the Banco D. João de Castro is an underwater volcano whose summit lies just ten metres below the surface. This exceptional site, which is rarely accessible, is one of the few remaining examples of active underwater volcanism in the Azores archipelago.

Thanks to the logistical support of Terceira-based diving centre Deep Blue Azores, we were able to organise an expedition at sea to film and document this unique site as part of the TerrAzores documentary.

Beneath the surface, the environment is both striking and fragile. Underwater fumaroles release bubbles of gas - mainly carbon dioxide and hydrogen sulphide - and bear witness to hydrothermal activity that is still present. The seabed is marked by a variety of deposits, high temperatures and aquatic life adapted to these very special conditions.

This dive reveals a geodiversity that is invisible from land, yet very real. It shows that the volcanism of the Azores is not limited to the craters and flows visible on the surface: it extends beneath the waves, into a world that is still little explored but essential to understanding the dynamics of the islands.

The Banco D. João de Castro is a rare window on the Earth's interior, a place where the living and the geological coexist in an unstable and fascinating balance.