Risks and contingency

Unforeseen circumstances, collapse of a borehole from unstable sands, adverse environmental conditions, hardware failures, or unusually slow penetration could result in insufficient time being available to complete the entire operations plan for Expedition 333. In anticipation of challenging and fluctuating environmental conditions, we have included a range of contingency options for the entire expedition in the operations plan and time estimate. To balance all of the priorities, each site is allocated a fixed limit for the maximum number of operational days. In addition, one possibility is that a maximum of eight days delay in the start date of Expedition 333 may occur, in case of severe delay during installing the long-term borehole monitoring system (LTBMS) at Site C0002 during Expedition 332. Even if this happens at the beginning of the expedition, the Expedition 333 science party will board the ship as scheduled and prepare for the expedition while Expedition 332 scientists finish working on installing the LTBMS.

Figures F7 and F15 show the drilling sequence and decision trees for contingencies if Expedition 332 finishes early or is delayed at the beginning of Expedition 333 or any of expedition targets finish ahead of or behind the planned schedule during the expedition period. It is important to note that this contingency plan is based on our state of knowledge at the time of this writing and modification may be required as additional information becomes available, including recommendations from the NanTroSEIZE PMT. Within our primary operations plan, we have identified several potential contingency options in the case of hole problems and/or time constraints (Fig. F15). If coring operations at any of the three sites require significantly more time than allocated to reach the total depth target, we do not plan to rebalance any of the remaining scientific objectives.

Kuroshio Current

The Kuroshio Current is a swift western boundary current that presents substantial risk to all expedition operations. If we encounter the maximum Kuroshio Current strengths at any given drill site, any operations and measurements may be risky as previous work in the region demonstrated that current related vibrations are potentially damaging to all hardware and tools deployed. The axis of the current migrates and meanders significantly and unpredictably (Fig. F16), so efforts will be made to monitor its location and velocity using available online resources with forecasts for a few months in advance without accurate and precise predictions.