Significant temperature changes in a steam-rich fumarolic gas from a deep hole in the Izu-Oshima volcano, Japan, were observed prior to a series of earthquake swarms and submarine volcanic eruptions which occurred off the eastern coast ofthe Izu Peninsula, about 40 km NE of the Izu-Oshima volcano, in July 1989. We suggest that temperature changes indicate that the Izu-Oshima volcano and the submarine volcanic cone, the Teishi knoll, are linked and that upward movement of Teishi magma resulted in a gas pressure decrease of the Izu-Oshima magma. This new suggestion of a link between two magma systems over such large distance may be of great significance for understanding arc volcanism. Our observation may be of use in the future prediction of volcanic eruptions in the Izu area. ¿ American Geophysical Union 1991