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The SE end of Graciosa, the northernmost of the central Azorean islands, contains a small 0.9 x 1.6 km caldera with active fumaroles. The 402-m-high SE caldera rim is the high point of the small 4 x 8 km island. The caldera has been the source of eruptions producing significant tephra falls, pyroclastic flows, lahars, and lava flows. An important fumarole field is located in a volcanic cave inside the caldera, and a submarine fumarole occurs off the NW coast of Graciosa. Scoria cones erupted along several widely spaced NE-SW-trending fissures fed a youthful lava field that forms the NW end of the island. The most recent eruption from Pico Tomao, NW of the caldera, produced a lava flow during the mid-to-late Holocene that reached the eastern coast NW of the village of Praia.
Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).
|Start Date||Stop Date||Eruption Certainty||VEI||Evidence||Activity Area or Unit|
|1950 BCE ± 1400 years||Unknown||Confirmed||Ar/Ar||San Tamao|
This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.
|Feature Name||Feature Type||Elevation||Latitude||Longitude|
|Serra das Fontes||Shield volcano|
|Timao, Pico||Pyroclastic cone|
|The small 4 x 8 km island of Graciosa is seen in this NASA Space Shuttle image with north to the upper left. Cloud banks partially obscure the SE end of the island, which contains a small 0.9 x 1.6 km caldera with active fumaroles. Scoria cones are found over much of the island, and several widely spaced NE-SW-trending fissures fed a youthful lava field that forms the NW end of the island.
NASA Space Shuttle image ISS004-E-10893, 2002 (http://eol.jsc.nasa.gov/).
|The Caldeira area of Graciosa is seen in this aerial view from the SW with the village of Luz at the center of the image. The small, 0.9 x 1.6 km caldera at the SE end of the island contains active fumaroles. The 402-m-high SE caldera rim is the high point of the small 4 x 8 km island. The most recent eruption from Pico Tomao, NW of the caldera, produced a lava flow that reached the eastern coast NW of the village of Praia.
Photo by Angrense, 2007 (Wikimedia Commons).
The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.
Larrea P, Wijbrans J R, Gale C, Ubide T, Lago M, Franca Z, Widom E, 2014. 40Ar/39Ar constraints on the temporal evolution of Graciosa Island, Azores (Portugal). Bull Volc, 76:796.
Mitchell-Thome R C, 1976. Geology of the Middle Atlantic Islands. Berlin: Gebruder Borntraeger, 382 p.
Neumann van Padang M, Richards A F, Machado F, Bravo T, Baker P E, Le Maitre R W, 1967. Atlantic Ocean. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 21: 1-128.
Zbyszewski G, Candido de Medeiros A, Veiga Ferreira O da, Torre de Assuncao C, 1972. Geologic map of Ihla Graciosa (Azores). Servicos Geologicos Portugal, 1:25,000 scale map with 31 p text (in Portuguese).