Geophysical studies of Erebus volcano, Antarctica, from 1974 December to 1982 January

Abstract

Seismic, infrasonic, and magnetic induction recordings and eruption observations during expeditions to Mount Erebus in December-—January of 1974–75, 1975–76, 1978–79,1978–81 and December 1981 are reported. Erebus IS umque in its high-latitude location within a tectonic plate and its persistent lava lake of phonolitic composition. In an aseismic region, more than 100 volcanic earthquakes per day occur in the energy range of 0.2-200000 J (M^L–2 to 1). Foci Iie mostly within the edifice of the vo1cano with a concentration of B-types near the crater. Preliminary Pvelocity determinations are 1.6 km/s in the summit cone (from crater explosions),4.5 km/s in the main edifice (from distant earthquakes), 6.5 km/s in the underlying basement, and 7.5 km/s at about 7 km below sea level (from refraction surveys). The b-value is 1.5 for earthquakes below 100 J and 0.6 for the larger earthquakes which accompany the average 3.6 ± 2.7 strombolian eruptions per day. Large earthquakes (and eruptions) are about 10 times more frequent between 14^h and 18^h UT than between 12^h and 14^h UT. The level of seismic activity is similar from year to year, but the eruptions vary from cannon like explosions typical of 1974 to roanng gas emIssIons typical of 1981.The seismic and infrasonic wave Received August 1983, accepted July 1984 frequencies are related and vary over a range factor of about 10.The diameter of the eruptmg area has similar variation. Sometimes the infrasonic onset just preceded the explosion earthquake. In others, forerunning tremor preceded explosions by up to 45 sand was observed to accompany hissing, and rise of lava, in the exploding vent; otherwise volcanic tremor is absent.Magnetic induction signals, with on sets simultaneous with the earthquake, accompany the larger and lower frequency infrasonic/ seismic events, and are interpreted as due to the movement of conducting magma in the earth§ magnetic field.The study is continuing in the International Mount Erebus Seismic Study (lMESS) which began in November 1980.