Sete Cidades

Sete Cidades' caldera formed approximately 22,000 years ago in a catastrophic collapse, creating a 5-km-wide depression that is one of the largest calderas in the Azores.

The twin caldera lakes — Lagoa Azul (Blue Lake) and Lagoa Verde (Green Lake) — were voted one of the Seven Natural Wonders of Portugal in 2010.

At least 22 post-caldera eruptions have occurred at Sete Cidades, with a nearly circular ring of six Holocene pyroclastic cones on the caldera floor marking the most recent vents.

The 1444 eruption was the last VEI 4 event at Sete Cidades and occurred less than a decade after Portuguese settlement of São Miguel, disrupting the fledgling colony.

Four of the last five eruptions at Sete Cidades originated from submarine vents off the western coast, indicating that the volcano's magmatic plumbing extends well offshore.

The volcano's trachytic magma composition makes its eruptions significantly more explosive than basaltic eruptions typical of mid-ocean ridges.

Sete Cidades sits at the Azores Triple Junction where three tectonic plates — Eurasian, Nubian, and North American — interact, one of only a handful of triple junctions on Earth.

The village of Sete Cidades (population ~800) sits on the caldera floor, making it one of the few inhabited volcanic calderas in Europe.

The 1811 submarine eruptions produced two separate events in the same year, generating floating pumice rafts that disrupted Atlantic shipping lanes.

Ferraria, a geothermally heated ocean swimming area on the volcano's southwest coast, reaches temperatures of up to 40°C where volcanic hot springs meet the Atlantic.