Between May 1983 and January 1984, the RSP recorded acoustic waves (T-phase) from three shallow submarine eruptions at Macdonald Seamount. On 17 May 1983, eruptive activity began gradually with a few explosive sequences and lasted 4.5 days until 21 May. Activity resumed explosively on 27-28 October and continued for 15 hours with numerous explosive sequences. On 24 December, activity began gradually with no explosive sequences and continued for almost 10 days until 3 January 1984. This last event was the 12th and longest eruption recorded since the volcano was discovered in 1967.

Geological Summary. Discovered by the detection of teleseismic waves in 1967, Macdonald seamount (also known as Tamarii seamount) rises from a depth of about 1,800 m to within 27 m of the ocean surface at the eastern end of the Austral Islands. The basaltic submarine volcano marks the site of a hotspot that was the source of the Austral-Cook island chain. The summit, 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, Lab. de Géophysique, Tahiti.