Arcos do Calhau, Terceira: Azores' volcanic arch dive

Descending into Arcos do Calhau, you'll immediately encounter a rocky plateau at a comfortable 10 metres. This initial depth provides an excellent orientation point as you begin to explore the distinctive volcanic topography. The site's namesake — two impressive lava arches — become visible almost immediately, inviting you to navigate through their natural formations. Sunlight filters through the archways, creating a dynamic play of light and shadow, truly immersing you in the geological history of the Azores.

The journey through the arches leads you into deeper territory, with the volcanic structures extending down to 20 metres. As you move beyond the initial plateau, the environment transforms, revealing the intricate details of the lava flows that shaped this underwater landscape. The arches themselves are not merely passages but vibrant habitats, offering shelter and foraging grounds for a variety of resident species, making every turn a potential encounter.

Within the crevices and underhangs of the lava formations, you'll find yellow anemones (Actiniaria) clinging to the rocks, their colours contrasting with the darker volcanic stone. Keep a close watch for moray eels (Muraenidae) peeking from their hidden spots, their watchful eyes following your progress. These nocturnal hunters are often seen during the day resting in their territories, adding a sense of wildness to the dive.

The rocky bottom and arch structures are also home to a selection of reef fish. Look for the vibrant colours of Turkish wrasse (Labridae), darting in and out of cover. Damselfish (Pomacentridae) are omnipresent, forming small aggregations around the more sheltered areas of the site. Their constant activity brings a lively energy to the volcanic seascape, as they feed and interact within their immediate environment.

As you explore the deeper sections of Arcos do Calhau, keep an eye on the sandy patches adjacent to the rocky plateau. Here, you might spot common stingrays (Dasyatis pastinaca) camouflaged against the seabed. These graceful creatures often rest partially buried in the sand, and with a careful approach, you can observe their gentle movements as they navigate the area, a quiet counterpoint to the more active reef inhabitants.