After an increase in fumarolic emissions and weak ash explosions in May, fumarolic activity remained vigorous. An eruption on 19 June at 2230, accompanied by 2-3 minutes of weak rumbling, sent ash and gas to ~2 km. An early August explosion formed new fumarolic vents on the dome's N flank, ~70-100 m from the summit (figure 1).

Figure 1. September 1989 photograph by A. Samoluk, looking W at the new fumaroles formed by an August explosion on the dome's N side.

On a 16 September ascent of the dome, geologists G. Steinberg and S Tkachenko observed vigorous gas emission from several sulfur-encrusted fissures, and deep narrow craters ~2-3 m in diameter. Two mud flows (4-6 m wide) that extended 1.5-2 km down the dome's N side had destroyed areas of thick vegetation (bushes and bamboo). One flow reached Lake Lopastnye (figure 2). No juvenile material was found in the flows. A small mudflow deposit on the S side of the dome, and another on the W (previously seen 18 and 20 May; reported as E slope in 14:5) were also observed.

Figure 2. September 1989 photograph by A. Samoluk, looking S at two mudflows on the dome's N side. Lake Lopastnye is in the foreground.

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 and R. Bulgakov, Yuzhno-Sakhalinsk.