Alaska is considered one of the most seismically active areas in the world. Every 13 years, the country is struck by a “great earthquake,” registering at magnitude eight or larger. The state’s data also revealed that more than 1,000 earthquakes of varying magnitudes are detected in the large area the size of half of the continental US every month.
The most popular and strongest earthquake—with a magnitude of 9.2—recorded in Alaska occurred in 1964. Reports showed that it was the most destructive one ever documented in North America, killing 131 people. About 15 of those died during the initial tremors and the rest in the subsequent tsunamis and landslides. The earthquake not only led to water, sewer, and gas line breaks and widespread telephone and electrical failures, but also toppled telephone poles, buckled railroad tracks, split roads in half, and tore homes apart.
The 1964 Alaskan earthquake also triggered devastating tsunamis, landslides, and submarine slumps, causing massive property damage and loss of life. It also led to significant scientific breakthroughs in subduction earthquakes and how to minimize their destruction. The reason Alaska is prone to strong earthquakes is that the Gulf of Alaska sits at the boundary of two large tectonic plates.
According to National Geographic, an American pay television network and flagship channel that is owned by National Geographic Partners, the two plates form a subduction zone where the latter plate is being constantly forced under the former, creating an intense amount of friction that causes earthquakes when released. Indeed, earthquakes formed in the country can be deadly and devastating. Experts fear that it will not only create dangerous earthquakes but also deadly tsunamis.
Geologic Structure Suggests a Major Tsunami in Alaska
In 2017, scientists from the Earth Institute at Columbia University mapped a geologic structure under the seafloor of Alaska. The discovery indicates that the region is at greater risk of being hit by a tsunami than previously recognized. The researchers said that a tectonic plate on a fault line positioned like that could span several meters and push a tremendous amount of water toward the shore during an earthquake.
The same feature resembles one that produced the 2011 Tohoku tsunami off Japan, which killed over 20,000 people and melted down three nuclear reactors. Lead author Anne Bécel of Columbia University's Lamont-Doherty Earth Observatory said that this suggests that Alaska is particularly prone to tsunami generation. "The possibility that such features are widespread is of global significance,” she said.
According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the researchers surveyed parts of the Aleutian subduction zone, a nearly 2,000-mile-long fault that extends from Russia’s Kamchatka Peninsula all the way to the Gulf of Alaska. They created cross-section images of two tectonic plates that are ramming into each other using 3D-imaging equipment aboard the Marcus G. Langseth, a research vessel that Columbia operates on behalf of the National Science Foundation.
The team found out that a large part of one plate, which is roughly the size of Delaware, has broken off its main slab. This section could be propelled violently upward during an earthquake and generate an enormous tsunami. “A strong earthquake in the area could shake it loose and cause seventy-five-foot waves to head both north and south. This could devastate parts of the Alaska Peninsula, which is just sixty miles to the north. It could also affect areas as far away as the western coast of the US and Hawaii, although the wave wouldn’t be nearly so large by the time it traveled that far,” Bécel said.
The researchers also discovered a cluster of seismicity where the newly identified fault meets the plate boundary after analyzing small earthquakes in the region. According to them, this confirms that the fault may be active. Earthquake patterns also suggest that frictional properties on the seaward side of the fault differ from those on the landward side. "With that big fault there, that outer part of the plate could move independently and make a tsunami a lot more effective. You get a lot more vertical motion if the part that moves is close to the seafloor surface,” co-author Donna Shillington, a Lamont-Doherty seismologist, said.
Melting Glacier May Trigger a Landslide, Catalyzing a Major Tsunami
Recently, a group of scientists discovered that a melting glacier and potentially thawing permafrost have destabilized a massive slope in Alaska’s Barry Arm, a fjord just 60 miles east of Anchorage. They revealed that only a third of the slope is now supported by ice, which could trigger a landslide—a landslide that could catalyze an earthquake, prolonged heavy rain, or even a heatwave that could cause extensive melting of surface snow.
The researchers estimated that a sudden, huge collapse is possible within a year and likely within two decades. “It could happen anytime, but the risk just goes way up as this glacier recedes,” Anna Liljedahl, an Alaska-based hydrologist with the Woods Hole Research Center in Massachusetts, said.
According to the New York Times, an American newspaper based in New York City with worldwide influence and readership, the researchers saw through a computer model that a collapse of the entire slope could cause a tsunami that would start out at several hundred feet high. It is roughly estimated to be 500 million cubic meters of rock and dirt or several hundred times the volume of the Hoover Dam.
In a statement from the Alaska Division of Geological and Geophysical Surveys, they said that the glacier’s retreat "could release millions of tons of rock into the Harriman Fiord, triggering a tsunami at least as large as some of the largest in the state's recorded history." Thus, the Alaska Department of Natural Resources and the state Department of Fish and Game recently issued a warning that they "strongly recommend people avoid all the identified danger zones until the hazards can be adequately understood and characterized.”
The researchers said that this could happen as landfall-generated tsunamis are not uncommon in Alaska. For instance, the 2015 Taan Fjord landslide generated a 633-foot-high tsunami. What makes Barry Arm different is that it is larger and higher in elevation, which could be catastrophic. “The largest tsunamis we have witnessed in recorded history were generated by landslides in fjords. Luckily, most of these historical landslides have been remote and isolated, with very little impact on coastal communities,” Prof. Patrick J. Lynett of University of Southern California’s Viterbi School of Engineering said.