*3.3. Turbidity Currents*

As a proof-of-concept for simulating turbidity currents in the northern Gulf ofMexico, we employed *TURBINS* for a lock-release type simulation for a narrow slice along a specific pathway in the failure location. Initially, the normalized sediment concentration, a proxy for excess density due to suspended particles, was set to one in the lock-region and zeroed elsewhere (Figure 11A). When the lock was released, a gravity-flow with a height of 30 m started to travel down the slope, so at 4 h past the lock release, the current was about 10 km downslope (Figure 11B). The current became diluted as a result of entrainment of ambient ocean water, and its height was reduced below the original height of 30 m as it traveled down the slope. Within about 8 h, the current had traveled 15 km down-slope (Figure 11C).

**Figure 11.** Contours of sediment concentration at (**A**) 0 h, (**B**) 4 h, and (**C**) 8 h. Sediment concentration normalized to values between 0 and 1; 0 indicates clear water without any sediment.

The velocities resulting from the momentum balance are shown in Figure 12 for different stages of the turbidity current. With time, as the turbidity current traveled downslope, thinned and became diluted; its velocities decreased (Figure 12). At 4 h post-ignition, the turbidity current had speeds exceeding 1 m/s, but by 8 h post-release the velocities were much lower. As the current traveled along the bed, it generated a counter-flowing current above that moved in the opposite direction (Figure 12A,B). The calculated velocity at the front of the turbidity current decreased from over 1 m/s to about 0.75 m/s over a period of 10 h (Figure 12C).

**Figure 12.** Horizontal velocity (m/s) calculated by TURBINS downslope at (**A**) 4 h, and (**B**) 8 h. Note change in color scale between panels (**A**,**B**). (**C**) Time history of the front velocity of the current.

Figure 13 displays the modeled bed shear stress at two instants in time. A substantial level of bed shear stress exists along the current length as a result of the turbidity current created by the suspended sediment, which drives the flow. As the current decelerated, the bed shear stress value decreased. These levels of bed stress exceeded the critical shear stress levels for the seabed assumed by the suspended sediment transport model (~0.1 Pa, Table 1), indicating that the gravity flows could be auto suspending, though this process was neglected in this version of the modeling workflow.

**Figure 13.** Bed shear stresses (Pa) generated by a simulated down-canyon flowing turbidity current at (**A**) 4 h, and (**B**) 8 h after flow initiation at the shelf-slope break.
