Don Joao de Castro Bank (Portugal)

Status Unknown Eruption 1720 -13m
Submarine (Rift zone / Oceanic crust (< 15 km))

Don Joao de Castro Bank

Don Joao de Castro Bank is a large submarine volcano that rises to within 13 m of the sea surface roughly halfway between Terceira and San Miguel Islands. Pillow lavas form the base of the volcano, which is capped by basaltic hyaloclastites. A submarine eruption during December 1720 produced an ephemeral island that attained a length of 1.5 km and an altitude of about 250 m before it was eroded beneath the sea surface two years later. The volcano (also spelled Dom Joao de Castro) was named after the Portuguese hydrographic survey vessel that surveyed the bank in 1941. Two youthful parasitic craters, one tephra covered and the other sediment free, are located on the NW flank. The submarine volcano has an impressive shallow fumarole field and remains seismically active.

Two unusual-looking flank craters are visible in this side-viewing sonar perspective of the NW flank of Don Joao de Castro Bank in the Azores taken by U.S. Navy submarine NR-1. The two craters are 90 x 45 m wide. The left-hand and younger crater displays a floor consisting of a chilled lava lake with polygonal surface fractures. The right-hand crater is much less distinct because its surface is obscured by tephra deposits. The line at the right is the center track line of the sonar image.

U. S. Navy image courtesy of Rick Wunderman, 2003 (Smithsonian Institution).

Last updated 2019-08-04 00:28:03

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