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Report on Macdonald (Undersea Features) — December 1988


Scientific Event Alert Network Bulletin, vol. 13, no. 12 (December 1988)
Managing Editor: Lindsay McClelland.

Macdonald (Undersea Features) Frequent eruptive seismicity in 1988

Please cite this report as:

Global Volcanism Program, 1988. Report on Macdonald (Undersea Features) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:12. Smithsonian Institution.


Undersea Features

28.98°S, 140.25°W; summit elev. -39 m

All times are local (unless otherwise noted)

Seismicity . . . was substantially more vigorous in 1987 and particularly in 1988 than in previous years since 1977 (figure 1). Acoustic T-waves generated from a submarine eruption 11-17 November 1988 were the most intense since the Polynesian Seismic Research station began to collect data more than 25 years ago. Since the end of the 3-18 September eruption nearly continuous weak seismicity from Macdonald was detected 26 September-5 October, 12-24 October, and 12-14 December, and weaker more sporadic explosions 25-29 December.

Figure (see Caption) Figure 1. Histogram showing hours of detected activity at Macdonald Seamount from 1977-88. Arrows indicate explosive onsets of eruptions. [Data from a figure in 13:05 and a table in 13:12 are incorporated into this figure originally printed in 14:01]. Courtesy of J. Talandier.

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.