Megaslides, massive underwater landslides triggered by earthquakes, volcanic activity, and sediment flux, can have significant consequences on the formation of tsunamis. These extreme events, such as the sixth-largest recorded megaslide in the Surveyor Fan in the Gulf of Alaska around 1.2 million years ago, can result in catastrophic tsunamis on the surface. With an area of at least 16,124 square kilometers and a preserved volume of 9,080 cubic kilometers, the magnitude of these megaslides is truly awe-inspiring.
A recent study published in Geophysical Research Letters by Sean Gulick and colleagues delves into the details of the Surveyor Fan megaslide. By utilizing images from seismic reflection surveys and ground truth data from drilling efforts in the Gulf of Alaska, researchers were able to uncover the existence of the slide and examine the seafloor topography before and after the event. The study suggests that the megaslide was likely triggered by a large earthquake during the Mid-Pleistocene Transition (MPT), a period between 0.6 and 1.2 million years ago characterized by longer glacial-interglacial cycles.
The findings of the study shed light on the factors that contribute to the formation of megaslides and their potential to generate tsunamis. The researchers point to sediment buildup and flux during the MPT, caused by extensive ice extents, as a key factor in slope instability that may have led to the megaslide. This highlights the intricate relationship between geological processes and seismic events in triggering underwater landslides.
While seismic activity continues in the region, the researchers note that the occurrence of megaslides similar in magnitude to the Surveyor Fan event has decreased. This is attributed to changes in sediment flux, seismic strengthening, and sediment deposits from ice streams on the continental shelf, which contribute to slope stability. As sediment continues to accumulate along the Alaska margin, the likelihood of large-scale slope failures decreases due to the reduced critical wedge taper.
Understanding the mechanisms behind megaslides and their relationship to tsunami formation is crucial for mitigating the risks associated with these underwater events. By studying past occurrences and their implications, researchers can better predict and prepare for potential tsunamis triggered by megaslides in the future.
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