Global Volcanism Program

Volcanoes of the World

Don João de Castro Bank

Volcanic Activity Reports

Don João de Castro Bank is a large submarine volcano that rises to within 14 m of the sea surface roughly halfway between Terceira and San Miguel Islands. A submarine eruption (with a Volcanic Explosivity Index of 3) 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 submarine volcano has an impressive fumarole field and remains seismically active. The area was charted in 1941.

Index of Volcanic Activity Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

03/89 (SEAN 14:03) Seismicity since May 1988 summarized

07/97 (BGVN 22:07) Magnitude 5.5 earthquake and associated seismic swarm

Complete Contents of Volcanic Activity Reports

All information contained in these reports is preliminary and subject to change.

[Don João de Castro Bank information only; extracted from a summary of significant seismic activity in the E Azores since May 1988.]

"A small swarm of earthquakes occurred within the volcano Don João de Castro Bank (figure 1, zone 4) 3-5 October. Sixty-two earthquakes were recorded; no harmonic tremor was detected. A felt earthquake occurred in the same area 23 October; it had intensities of MM IV-V on Terceira and MM III-IV on the N coast of Sao Miguel."

Figure 1. Sketch map showing islands in the eastern Azores. Approximate epicenters of the 3-5 October 1988 swarm at the submarine volcano Don Joao de Castro Bank (4) and the 21 November 1988 and 21 January 1989 earthquakes in the Hirondelle Basin (6 and 7) are shown. Courtesy of R. Moore.

Information Contacts: A. Rodrigues da Silva, Consorcio Geotermico de S. Miguel; R. Moore, USGS; National Institute of Meteorology and Geophysics, Portugal.

On 27 June 1997 at 0439 a strong earthquake struck the Azores Archipelago. This main shock reached M 5.5 and was felt with maximum intensity of V on the Modified Mercalli Scale at Terceira and São Miguel islands; in the islands of São Jorge, Pico, and Faial, the respective maximum intensities were III/IV, III/IV, and II/III.

The epicenter was in the vicinity of Don João de Castro bank (figure 9), a submarine volcanic structure. An earthquake swarm began the same day. During one month about 2,000 such events were registered at a reference seismic station on São Miguel island. Approximately 45 earthquakes with M >4 were registered at Terceira island. By 12 September about 2,100 earthquakes had occurred but by then the swarm had declined to 1 or 2 small events a day.

Figure 9. Epicenters during part of the seismic swarm at the Don João de Castro bank (Azores Archipelago), 27 June to 2 August 1997. Provided by SIVISA; courtesy of J.L. Gaspar.

In 1720 AD the Don João de Castro Bank produced an eruption with a Volcanic Explosivity Index (VEI) of 3. After four days an ephemeral, 1-km-long island was created. The area was charted in 1941. Seismic swarms in this general region were also noted in 1988 and 1989 (Bulletin v. 13, no. 10, and v. 14, no. 3).

Information Contacts: Azores Seismological Surveillance System (SIVISA) (Email: sivisa@mail.telepac.pt), coordinated by a) J.L. Gaspar, Azores University Centre of Volcanology, 9500 - Ponta Delgada, Azores, Portugal and b) Luísa Senos, Meteorological Institute, 9500 Ponta Delgada, Azores, Portugal.