Submarine Mass Movements and Their Consequences

Untitled

“…The sediment liquid limit is ~65% and the plastic limit is ~35%, yielding a plasticity index of 30% (Expedition 308 Scientists, 2006;Urgeles et al, 2007). The clay minerals of the silty clays average 73% illite-smectite, ~80% of which is smectite (Day-Stirrat et al, 2010).…”

“…Experimental deformation of samples from Sites U1322 and U1324 provides clues to the mechanical processes of failure (Urgeles et al, 2007;Dugan and Germaine, 2009). We present the previously unpublished plots of stress, strain, and fluid pressure of four isotropically consolidated undrained triaxial experiments of the nine summarized in Urgeles et al (2007) (also see Supplemental Table File 1 for details of experiments).…”

“…We present the previously unpublished plots of stress, strain, and fluid pressure of four isotropically consolidated undrained triaxial experiments of the nine summarized in Urgeles et al (2007) (also see Supplemental Table File 1 for details of experiments). Three experiments (Figs.…”

“…Breakouts and extrusive failure are recorded from 90 mbsf. This is the depth at which the liquidity index measured in samples of the Ursa Basin approaches zero [liquidity index = (natural water content -water content at plastic limit)/(water content at liquid limit -water content at plastic limit)] (Lambe and Whitman, 1969); i.e., the natural water content of the samples taken from the borehole is close to or at the plastic limit, denoting a transition from a plastic to a more brittle behavior (Urgeles et al, 2007). Because the muds at Site U1322 are very low permeability (10 -17 to 10 -18 m 2 ; Binh et al, 2009;Schneider et al, 2008), the failure, occurring within minutes of cutting the hole, is undrained.…”

“…Site 1322, a vertical borehole in the Gulf of Mexico, is in an extensional tectonic environment (Urgeles et al, 2007;Sawyer et al, 2009a) characterized by active landslides (Fig. 1); the vertical stress is assumed to maximum principal stress (Tables 1 and 2).…”