Yonemaru and Sumiyoshiike are basaltic maars formed in coastal lowland deposits north of the Aira caldera, on the SW and SE flanks of the small Pleistocene Aojiki cone. The three features are also known as the Kamo Volcanic Field. The maar eruptions occurred during a period of rising sea level at the beginning of the Holocene. The 500-m-wide Sumiyoshiike was created about 7,000 years ago. The larger, 1.2-km-wide Yonemaru erupted about 2 km W of Sumiyoshiike about 6,500 years ago and produced pyroclastic surges that traveled 4 km from the vent.