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doi:10.2204/iodp.sp.339.2011

Risks and contingency

The principal risks identified include

• Sandy lithologies alternating with silt/clay, leading to a potential for hole instability;

• MOW flows between 500 and 1400 mbsl with variable but high bottom-current velocity, which is close to 300 cm/s at the Strait;

• The presence of gas-prone sediments at some sites and depths, leading to a potential for core expansion on deck;

• The presence of submarine cables on the seafloor (or partially buried by sediment drift) that might be damaged during drilling operations;

• Commercial marine fishing and shipping traffic, military training operations (Army submarines) area, disused explosive dumping areas; and

• Adverse weather conditions.

All of these factors may affect coring and drilling operations, but most are considered of minor significance or are away from the proposed locations.

Plans for mitigation of effects and for contingency include the possibility of using heavy mud or casing to increase the stability of the hole and keep the hole from collapsing. A TV survey of the seafloor before coring is planned for all sites to prevent the hitting a submarine cable accidentally.

The drilling sites are within Portugal and Spain's Exclusive Economic Zones and obtaining clearances to drill will be necessary.

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