Alaska Landslide Detection Advances with NOAA Tsunami Monitoring in Prince William Sound

Since August 2023, the Alaska Earthquake Center has been actively monitoring unstable slopes in Prince William Sound using seismic instruments. According to Michael West, the center's director, the initiatives are in their nascent stages, aiming to reduce exposure to landslide and tsunami risks. This interdisciplinary approach is supported by multiple agencies, including the U.S. Geological Survey and the Alaska Division of Geological and Geophysical Surveys, and is crucial for identifying the conditions under which landslides occur.

The focal point of this initiative is Barry Arm, where the experimental setup serves as a critical model for other landslide-prone regions in the United States. The test area is set to expand significantly to cover Southern Alaska, integrating most of the seismic network. In this collaborative project, Ezgi Karasözen, a research seismologist, plays a pivotal role by developing a computer-based method that analyzes seismic data from Prince William Sound every 30 seconds to detect potential landslides. Her algorithm scans data from several dozen stations, providing near-real-time landslide detection—a crucial factor for Alaska's steep coastal slopes that are at risk of triggering tsunamis.

Previously, a landslide in Greenland resulted in a 200-meter-high tsunami, demonstrating the catastrophic potential of such events. Since the monitoring began in Alaska, 28 landslides have been detected in real time, with two in the previous summer alone at Pedersen Bay and Surprise Glacier generating small tsunamis. Insights from the monitoring of the Surprise Inlet landslides have been published, offering a novel understanding of real-time landslide detection in a region where such events have historically gone unnoticed.

Landslides, encompassing a broad range of rapid land movements, are scientifically categorized under "mass movement." Specifically, in Prince William Sound, these movements typically involve substantial rock volumes that generate distinctive seismic signals. West highlights that Alaska's topography, composed of unstable and aged mountainsides, predisposes the region to frequent collapses. The observed increase in landslide occurrences has led to the informal designation of late summer as a "landslide season," correlating with increased precipitation destabilizing slopes.

While efforts in Prince William Sound are advancing rapidly, not all landslides can be detected using seismic methods. Mudslides in Southeast Alaska, for instance, occur in saturated soil and produce high-frequency seismic waves that are difficult to monitor. Karasözen notes that only large, deep-seated collapses can generate detectable long-period seismic waves over a broad area. The Earthquake Center’s efforts currently target a 220-kilometer radius around Barry Arm, where rapid detection and confirmation is key to contributing valuable data to tsunami modeling.

It takes about 20 seconds to process a landslide detection, signifying critical time for areas like Barry Arm, where tsunamis could form quickly in response to landslides. The prospect of a 2-meter high wave reaching Whittier within 20 minutes underscores the importance of efficient monitoring. Real-time seismic detection marks a significant change, enabling collaboration with other agencies to enhance hazard assessment.

Moving forward, the challenges of expanding detection across Alaska remain, given the vastness and varying distances between existing seismic instruments. Karasözen emphasizes the need for a swift detection strategy tailored to the state's seismic network, contemplating whether to establish multiple grid searches or a comprehensive system.

Collaborative efforts continue as part of a multi-agency initiative to develop a thorough inventory of landslide occurrences across Alaska. Establishing patterns over time and location would facilitate targeted monitoring or early warning systems. While full early warning capacities are not yet achieved, this real-time seismic monitoring provides greater clarity on Alaska’s landslide risks and sets the groundwork for future advancements in early warning systems.