Site U1436

International Ocean Discovery Program (IODP) Site U1436 was drilled as a geotechnical survey requirement for proposed D/V Chikyu drilling at Site IBM-4. Site U1436 is located at 32°23.88′N, 140°21.93′E in the Izu arc (Figure F1). It lies 1776 m below sea level in the western half of the Izu fore-arc basin, about 60 km east of the arc-front volcano Aogashima (Figures F1B, F2) and 170 km west of the axis of the Izu-Bonin Trench (Figure F3). Because Site U1436 is a geotechnical hole for proposed Site IBM-4, the first part of this section focuses on the background and objectives for Site IBM-4 ultradeep (~5.5 km) drilling to arc middle crust, which is inferred to represent juvenile continental crust. However, Site U1436 yielded a rich record of Quaternary explosive volcanism; therefore, the second half of this section provides background on Quaternary volcanism in the Izu-Bonin arc and objectives for ash recovered.