Residents of the E end of Hokkaido heard an explosion on 20 July at 1325. The explosion was not recorded by seismographs or microbarographs in E Hokkaido. Tiatia, approximately 50 km to the E, was obscured by fog. The next morning, the crew of the JMSA ship Kunasiri observed a white cloud rising 600 m from Tiatia, but heard no explosions. No ashfall was found (in Japan) on 20 or 21 July.

Geological Summary. Chachadake, also known as Tiatia, consists of a beautifully symmetrical cone that rises above the broad rim of an erosionally furrowed, 2.1 x 2.4 km wide caldera. The edifice occupies the NE tip of Kunashir Island and morphologically resembles Mount Vesuvius. The pristine-looking conical central cone, mostly formed by basaltic to basaltic-andesite strombolian eruptions, rises 400 m above the floor of the caldera and contains a 400 x 250 m wide crater with two explosion vents separated by a linear septum. Fresh lava flows cover much of the SW caldera floor and have overflowed the rim, extending to the foot of the older somma, which formed during the late Pleistocene or early Holocene. A lava flow from a flank cone on the northern caldera rim reached the Sea of Okhotsk. A major explosive eruption in 1973 followed an initial historical eruption in 1812.

Information Contacts: JMA, Tokyo.