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Complex, volatile coast makes preparing for tsunamis tough in Alaska

Tsunami damage
Enlarge / Damage from the 1964 earthquake and tsunami in Kodiak, Alaska.

On an overcast day in September, Heidi Geagel negotiates familiar potholes on a gravel road in Seldovia, Alaska. Cresting a hill topped with a small chapel, her town spreads out below—in the bay, gently rocking fishing boats; onshore, the Linwood Bar & Grill, the Crab Pot Grocery, and a couple dozen homes on stilts.

Geagel, Seldovia’s city manager, turns around to three people sitting in the back seat, who partner with the United States’ National Tsunami Hazard Mitigation Program and have traveled in from Anchorage and Fairbanks for a meeting with community leaders about tsunami hazards. She points out how much of the landscape could be underwater if one of the giant, fast-moving waves were to hit: “Pretty much the entire map of Seldovia is in the inundation zone, except for this hill.”

Alaska is uniquely vulnerable to two types of tsunamis. The first, tectonic tsunamis, are linked to the long string of volcanic islands that curves like a tail from the state’s southern tip; these islands mark the northern edge of the Ring of Fire, a geologically active zone that generates approximately 90 percent of the world’s earthquakes. Tracing those islands, deep under water, is the Alaska-Aleutian subduction zone, a trench where vast plates of hard rock overlap and friction slowly builds. Once or twice a year, the subduction zone generates earthquakes strong enough to trigger tsunami alerts; every 300 to 600 years or so, it ruptures in a megaquake that sends devastating tectonic tsunamis to Alaska’s shores.

The state’s 34,000 miles of wild shoreline make a second, lesser-known type possible, too: landslide tsunamis. Alaska’s southern coast is lined with active volcanos and hundreds of fjords ringed by unstable cliffs and, in the deep water below, a thick layer of silty sediment. Relatively small earthquakes, common in Alaska, shake that unstable landscape, causing landslides above and below sea level that displace massive volumes of water. The resulting tsunamis may hit coastal communities within minutes. And as climate change accelerates glacier melt and the subsequent erosion in those regions, those landslide tsunamis are increasingly likely.

The mix of hazards means that “in Alaska, we have the capability to have a very bad day,” as state earthquake geologist Barrett Salisbury, one of the tsunami scientists, puts it.

Seldovia sits about 137 miles as the crow flies southwest of Anchorage on the tip of the rugged Kenai Peninsula, directly above where the tectonic plates meet. It’s one of 159 communities that dot Alaska’s coast, including tourist hubs that host 4,000-passenger cruise ships, tiny Russian Orthodox villages, and the settlements of many of Alaska’s 228 federally recognized Indigenous tribes. Small and isolated, it’s a case study for the layers of complexity that make Alaskan communities especially vulnerable.

It’s hard to plan for a tsunami. Tsunami science is practically in its infancy, having only emerged as computer modeling became possible in the 1980s. Scientists in Alaska lack the technology required to forecast tsunamis before they hit the state because they simply happen too quickly. For many Alaskans, the state’s last major tsunami, which hit in 1964, is a distant memory. False alarms cause evacuations at least once a year, leaving people to wonder why they must leave without any waves to show for it. Those challenges are compounded by a culture that can be wary of outside experts. “I know the history,” says Elena Suleimani, a tsunami modeler on the state team, who works at the Alaska Earthquake Center at the University of Alaska Fairbanks.

“I know every single detail of what happened in ’64. And the people who live there, they don’t.”

As community leaders and scientists prepare for the next big wave, they struggle with a perennial question: How can they convince people they’re at risk from a disaster that’s unpredictable, can skip many generations, and is guaranteed to be catastrophic when it comes?

A deadly one-two punch

In Seldovia, homes are perched on stilts above water that could rise quickly during a tsunami. The small town sits on the tip of the rugged Kenai Peninsula, directly above where the tectonic plates meet.
Enlarge / In Seldovia, homes are perched on stilts above water that could rise quickly during a tsunami. The small town sits on the tip of the rugged Kenai Peninsula, directly above where the tectonic plates meet.

On March 27, 1964, the second largest earthquake in recorded history, magnitude 9.2, struck off Alaska’s southern coast. Streets in Anchorage cracked in half and a whole neighborhood fell into the sea. Within minutes, the underwater slopes along parts of the shoreline failed, generating local tsunamis.

Then, the tectonic tsunami hit, inundating communities repeatedly for hours. More than 20 tsunamis struck Alaska in all, killing 106 people across the state and causing $284 million in damage. In Seldovia, the ground shook for about three minutes, then permanently sank by 3.5 feet. The highest wave of the tectonic tsunami that reached the town, at 26 feet, wasn’t itself significant, as it arrived at low tide. But on the next extreme high tide, the town was underwater and had to be razed and rebuilt.

Darlene Crawford, a Seldovia Village Tribe elder, remembers holding the cupboards shut as her house shook around her, seemingly for an eternity, then herding her four young children up a hill to high ground on that cold March evening. The effects of the Good Friday Earthquake linger today, she said—the urban renewal project to raze the town divided the community, and only one cannery returned, transforming the crab fishing-based economy. “It really changed life in Seldovia,” she said. “The town was blank for quite a while.”

Still, Seldovia fared better than most, in part because the town faces the sheltered Cook Inlet. On the opposite side of the Kenai Peninsula, facing the open ocean, communities like Seward, where Crawford’s parents lived, weren’t so lucky. There, waterfront warehouses and fuel storage tanks slid into Resurrection Bay, then were returned to shore within minutes by fiery waves more than 30-feet high. The Alaska Native village of Chenega, on an island near Seward, lost a third of its population and was never resettled. Its residents initially scattered across Alaska before building a new community on a nearby island.

Next time, Seldovia might not be as lucky. Tsunamis are as unpredictable as they are inevitable. And if the next megaquake strikes at high tide, the waves could wipe Seldovia off the map.

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