Integrated Ocean Drilling Program (IODP) Expedition 311 was originally scheduled with 22 on site operational days. In May 2005 in response to a significant change on the IODP U.S. Implementing Organization (USIO) riserless vessel schedule, an additional 15 operational days was added to Expedition 311 "Cascadia Margin Gas Hydrates." The purpose of this addendum is to provide an updated operational and scientific plan for the expedition that accounts for the additional days that have been assigned to Expedition 311.
The revised schedule includes a port call in Astoria, Oregon (USA) on 16 September 2005 to embark the scientific party and a port call in Victoria, British Columbia (Canada) at the end of Expedition 311 on 28 October 2005. Expedition 311 is now scheduled to include a total of 37 operational days on site. The original operations plan, as described in the scientific prospectus for Expedition 311 (Collett, Reidel, Malone, and the Expedition 311 Project Team, 2005) included drilling and coring activities at five sites across the Northern Cascadia accretionary prism (table T1 in the original prospectus). The proposed Expedition 311 drill sites included a four-site transect identified by proposed Sites CAS-03B, CAS-02C, CAS-01B, and CAS-05D. The fifth drill site in the plan also included drilling an active cold vent identified as proposed Site CAS-06A.