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Report on Macdonald (Undersea Features) — September 1988


Scientific Event Alert Network Bulletin, vol. 13, no. 9 (September 1988)
Managing Editor: Lindsay McClelland.

Macdonald (Undersea Features) Two weeks of submarine eruptive activity

Please cite this report as:

Global Volcanism Program, 1988. Report on Macdonald (Undersea Features) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198809-333060


Undersea Features

28.98°S, 140.25°W; summit elev. -39 m

All times are local (unless otherwise noted)

Numerous shallow submarine explosions of moderate intensity occurred . . . from 2155 on 2 September until 5 September, recorded as acoustic waves (T-phase) by the RSP. Sporadic weak activity persisted from 6 September until the eruption's end at about 0700 on 18 September. Periods of activity were also detected 6-18 May and 11 June 1988. No explosions accompanied the onsets of active periods during August 1987-June 1988, suggesting to seismologists that the eruption may have been continuous during that time.

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.