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✅Submarine Eruptions and the Islands That Appear and Disappear

The geological nature of the central Atlantic massif, where the Azores archipelago is located, is sensitive to various seismic phenomena and some volcanic activity, which have affected the Azorean islands throughout their history. There are records of approximately three dozen volcanic eruptions since the islands were inhabited.

These circumstances have also led to submarine eruptions, which in some cases gave rise to islands that later disappeared. However, the known records do not allow us to determine exactly when and where these phenomena occurred, especially in earlier times. Nevertheless, recognized accounts indicate 26 eruptions over the nearly six centuries since the islands were settled, fifteen of which occurred at sea.

Léon Sonrel, a French author who studied the oceans, published a work in 1868 in which he dedicated two pages to Azorean submarine eruptions and “the birth and disappearance of islands due to earthquakes,” including an engraving of an éruption sous-marine aux Açores.

According to Sonrel, this eruption took place when a volcano became active on June 11, 1638, during an earthquake between the islands of Terceira and São Miguel, giving rise to an island that was later marked on a nautical chart published in 1682 by cartographer Johannus van Keulen.

In all known cases, particularly near the islands of São Miguel, Terceira, São Jorge, Pico, and Faial, both the landscape and maritime activities were temporarily altered by these submarine eruptions. Therefore, their inclusion among the most notable episodes in the maritime history of the Azores seems justified.

A Submarine Eruption in the Azorean Seas

Among the historical records of eruptions in the Azores, submarine eruptions stand out, some of which led to the emergence of islands:

• A probable eruption in 1638, which resulted in the appearance of an island midway between São Miguel and Terceira that later disappeared. On December 31, 1719, another eruption in the same location gave rise to a new island that remained until November 17, 1723. In 1947, the hydrographic vessel D. João de Castro surveyed the area and found a minimum depth of approximately 8 meters.

• Several eruptions near Ponta da Ferraria, west of São Miguel, occurring in 1638, 1720, and 1811, the latter giving rise to the so-called Sabrina Island.

• An eruption on July 10, 1757, off the north coast of São Jorge, about “100 fathoms away, more or less,” in which “eighteen islets emerged, some larger than others.”

• A submarine eruption about 9 miles from Ponta da Serreta, northwest of Terceira, which began on June 1, 1867, and for eight days displayed “large columns of water and steam, alongside boiling water in a whirlpool.”

• Two eruptions recorded in 1800 and 1902 near Ponta do Topo, at the eastern end of São Jorge.

• An eruption approximately 800 meters from Ponta dos Capelinhos, west of Faial, on September 27, 1957, which lasted until October 24, 1958, when the last lava emission occurred, creating an island that eventually connected to the mainland.

Besides the submarine eruptions that were precisely located, others were not sufficiently identified, although they were referenced in some texts. One such example is revealed in the Annaes da Ilha Terceira:

On October 10 [year 1720], there was a great earthquake, felt throughout most of the Azorean islands […]. On that day, a considerable fire appeared near Terceira, bursting from the sea […], and a fiery and smoky island was observed, with a prodigious amount of ash being thrown far away, clearly indicating volcanic origin, and a vast quantity of pumice stones was noticed near the new island.

Although the known maritime eruptions did not cause any human tragedies and, in the most recent case, even led to a significant voluntary migration of many families to the United States and Canada, they have always represented significant episodes in the maritime history of the Azores.

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