Effect of Seismicity and Tectonic‐Glacial Interactions on Submarine Megaslides

Abstract

Enhanced sedimentation at glacial margins can produce submarine megaslides (>10,000 km ³). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km ² in area and ∼9,080 km ³ in volume. Slope failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). With accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km ³, with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was triggered by a major sediment influx at the onset of the MPT, when glacial‐interglacial cycles shifted from 41 to 100 Kyr. The absence of repeat megaslides may reflect a changing balance between seismic strengthening and sediment flux, where later sedimentation driven by cross‐shelf ice streams results in thin, fluidized, non‐cohesive slides. Continued accretion of the Surveyor Fan and megaslide also reduces critical wedge taper, further inhibiting major failure.

Plain Language Summary

Sediment flux at glacial margins can produce submarine slides >10,000 km ³ in size (megaslides). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km ² in area and ∼9,080 km ³ in volume. Failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). Due to accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km ³, but with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was caused by the initial major sediment flux at the onset of the MPT, and that afterward only fluidized, thin, and non‐cohesive slides occurred. This is due to changing balance between seismic strengthening and sediment flux, and accretion of the Surveyor Fan and megaslide which reduces the critical wedge taper inhibiting major failure.

Key Points

• World's Fifth largest mapped megaslide documented beneath Surveyor Fan Gulf of Alaska

• Timing of slope failure linked to onset of mid‐Pleistocene glacial intensification

• Absence of later failures due to changing balance of sediment flux/seismic strengthening and negative feedbacks from critical wedge processes