U.S. News

On a cold, windy, wet summer evening last month, Pete Beachy giggled as he peered into his binoculars and prepared to do something even he admitted can seem very, very stupid. “There she is,” he muttered. “That’s a wave.”

Parked along the Seward Highway in Alaska, Mr. Beachy had spotted the first hint of foam curving around Bird Point, 30 miles southeast of Anchorage, and heading toward an inlet known as Turnagain Arm. The “wave” was a tidal bore, a twice-daily surge of water formed when the incoming high tide from the Pacific Ocean is forced into the narrow arm of Cook Inlet against the outgoing current.

The resulting breaker can reach 10 feet in height, with speeds of 10 to 15 miles an hour — and surfers can ride it for miles if they’re tough enough to withstand the cold and skilled enough to stay upright.

“One moment it’s still, and you’re looking up at the mountains and eagles and goats, and the next you feel like you have the entire ocean coming up behind you,” Mr. Beachy said. “It’s magical, man.”

Hydrologists have documented more than 60 tidal bores worldwide, but only about a dozen are surfable. The Turnagain Arm bore is among the world’s most accessible. The secret is getting out, to big-wave surfers seeking one of the world’s most unusual rides, and to a small but growing number of Alaskans who have embraced the homegrown extreme sport. The tourism agency in Girdwood, a nearby ski town, posts tide charts on its website highlighting the days with the biggest potential waves.

Every newcomer increases the risk, and fears the authorities will decide to shut their fun down.