Cabeço Gordo is the highest mountain, massive stratovolcano

Stratovolcano

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 and the largest geomorphological structure that forms the island of Faial

Faial Island

Faial Island , also known in English as Fayal, is a Portuguese island of the Central Group of the Azores....

. The mountain/volcano is 1,043 meters above sea level, consisting of a two kilometer wide caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

, that is 400 m in depth below the crater rim. From Cabeço Gordo, on a clear day, the islands of the central group of the Azores are visible: Pico, Sao Jorge, and Graciosa, although normally the caldera may be covered in clouds and fog.

History

Along the western edge of the Ribeirinha Volcano, the Central Volcanic Complex formed about 410,000 years ago, along with several structures that arose from tectonics. Evidence of this process has not been preserved due to subsistence, but it is generally believed that two formations (an Upper and Lower group) reflecting a geochemical variation that occurred about 16,000 years ago. The Lower group (from 410,000 years ago), was marked by the predominance of a Hawaiian/Strombolian eruptive process, that was composed of basaltic and benmoreitic rocks. The secondary, Upper group, was a highly explosive period (sub-Plinian in character), which produced a series of twelve deposits of pumice and surge deposits (pyroclastic flows of trachytic and benmoreitic).

Although the central volcano has not been active within the past two centuries, it has seen activity related to the eruption of Capelinhos

Capelinhos

The Capelinhos is a monogenetic volcano located on the western coast of the island of Faial in the Azores. It is part of the larger Volcanic Complex of Capelo, that includes 20 escoria cones and lava fields that are aligned west-northwest to east-southeast from the Cabeço Gordo caldera...

(1957–58). During this period, fumaroles in the caldera became active, and the minor lakes/swamps were dried-up by excessive heat.

Cabeço Gordo, due to its central nature, is part of each parish on the island (except for Matriz, Conceição and Angustias).

Geography

Cabeço Gordo is the main geomorphological unit, corresponding to a polygenetic volcano two kilometers at the top and one kilometer at the base. The walls of the crater rim are abrupt, although their slopes increase with altitudes. The superficial cover of the volcano is covered in pyroclastic material, such as pumice rock, phreatic and phreatomagmatic deposits, evidence of pyroclastic flows and lahars. The flanks of the stratovolcano also include the Morro de Castelo Branco and peninsula of denser material that have resisted erosion.