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Report on Macdonald (Undersea Features) — April 1988


Scientific Event Alert Network Bulletin, vol. 13, no. 4 (April 1988)
Managing Editor: Lindsay McClelland.

Macdonald (Undersea Features) Eight months of frequent eruptive seismicity

Please cite this report as:

Global Volcanism Program, 1988. Report on Macdonald (Undersea Features) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198804-333060


Undersea Features

28.98°S, 140.25°W; summit elev. -39 m

All times are local (unless otherwise noted)

During the past 8 months, the RSP has detected frequent seismic swarms from Macdonald Seamount. The recorded acoustic waves (T-phases) are generated during eruptions at the interface between lava and sea water. Seismicity was recorded 19 August-27 October, 1987; 28 December 1987-3 March 1988; and 28 March-26 April, 1988. With the exception of a strong signal in October, activity was weak and varied from continuous to sporadic. Seismologists suggested that the absence of explosive onsets for the swarms detected since August could indicate that activity has been quasi-continuous through the end of April and beyond.

Geological Summary. Discovered by the detection of teleseismic waves in 1967, Macdonald seamount (also known as Tamarii seamount) rises from a depth of about 1800 m to within 27 m of the sea surface at the eastern end of the Austral Islands. The alkali-basaltic submarine volcano marks the site of a hotspot that was the source of the Austral-Cook island chain. The summit of the seamount, named after volcanologist Gordon Macdonald, consists of a flat plateau about 100 x 150 m wide with an average depth of about 40 m. The summit plateau is capped with spatter cones that form steep-sided pinnacles. Most eruptions have been seismically detected, but in 1987 and 1989 pumice emission was observed from research vessels. Pumice rafts observed in the South Pacific in 1928 and 1936 may also have originated here.

Information Contacts: J. Talandier, LDG Tahiti.