An abrupt increase in white fumarolic emissions, accompanied by weak explosions of gas and black ash, was observed . . . 3-4 May. A seismograph in Kurilsk (~30 km from the volcano) recorded weak earthquakes at various depths and short-period volcanic tremor for the following 5 days [see also 15:2]. On 8 May at 1330, a strong explosion ejected a black ash column that reached 1,500-1600 m above the summit within 8 minutes. By 1402, winds were dispersing the plume. A low-frequency rumble was heard in Kurilsk and Goryachie Kluchi (9 km W) during the eruption, but witnesses on the Pacific coast (6-8 km S) heard no sounds. On 11 May, images from a NOAA polar orbiting satellite at 1400 and Japan's GMS satellite at 1900 showed no volcanic plume. Small ash explosions occurred after 14 May, and as of 26 May, steam/gas emissions were continuing. More than a week before the eruption, a report in the 25 April Sovetskii Sakhalin newspaper warned that the residents of Goryachie Kluchi village would be at risk if an explosion should occur.

Before the eruption, fumarolic activity was concentrated in the N block along a wide fracture that extended 250-300 m down the W slope from the summit. Geologists who flew over the volcano in a helicopter and airplane 10 days after the eruption (on 18 and 20 May) observed a narrow mudflow, ~20-30 m wide and 1 km long, on the E slope. Fumarolic activity was still visible in the upper portion of the N block fracture. Fumaroles were also observed in the saddle separating the blocks of the dome, near the E slope.

Further Reference. Abdurakhmanov, A.I., Zlobin, T.K., Markhinin, E.K., and Tarakanov, R.Z., 1990, The Ivan Groznyi volcano eruption on the Iturup Island in 1989: Volcanology and Seismology, no. 4, p. 3-9 (in Russian); v. 12, p. 423-430 (in English).

Geological Summary. The Etorofu-Yakeyama (Ivan Grozny) complex is located in the center of Iturup Island. It has a 3-3.5 km diameter caldera open to the south, where a large extrusive andesitic dome was emplaced. Several other lava domes of Holocene age were constructed to the NE; extrusion of these domes has constricted a former lake in the northern side of the caldera to an extremely sinuous shoreline. Recorded eruptions, the first of which took place in 1968, have been from the central Yakeyama (Grozny) dome.

Information Contacts: G. Steinberg, V. Ostapenko, and R. Bulgakov, Yuzhno-Sakhalinsk; G. Bogoyavlenskaya and I. Menyailov, IV; T. Baldwin, NOAA/NESDIS.