GIRDWOOD, Alaska (AP) — The full moon and its alignment with the sun combined to send a short wall of water rushing back into a narrow Alaska inlet, creating the largest bore tide this year and an opportunity for surfers and kayakers to ride a rare wave to the beach.
The wave Tuesday evening was about 3 feet high, not much compared to what people in Hawaii or California are accustomed to, but exciting enough by Alaska standards.
"That's a big wave for Alaska, aside from tsunamis," said Ellen Franklin, who was among hundreds of people who filled highway pullouts to see the tide come rushing back in, led by an advancing wall of water resembling rapids.
The wall spanned across Turnagain Arm — the 3-mile-wide body of water that stretches from Anchorage south about 25 miles to the resort community of Girdwood. It covered the inlet from beach to beach, quickly filling in mudflats that were exposed when the tide went out.
The bore tide also drew a few surfers and kayakers hoping to take advantage of a real wave in Alaska.
"It was fantastic," said surfer Sue Ives of Anchorage. "The water was glassy. I guess this is supposed to be the biggest bore tide of the year, so it was a pretty great ride."
The bore tide is an actual tidal wave, said Michael Lawson, a meteorologist with the National Weather Service in Anchorage.
"The bore tide is a true tidal wave in the sense that it's controlled by the tide and is largely due to the gravitational influence of the sun and moon."
Bore tides happen all over the world, but Anchorage's Turnagain Arm and Knik Arm are the only places in the United States where they occur regularly, he said.
That's because of the orientation of Turnagain Arm and the shallow, narrow terrain along the strip of water stretching about 25 miles from Anchorage south to the resort town of Girdwood.
Bore tides happen every day here, Lawson said, but whether there's a visible wave associated with it depends on the weather and the exact nature of the tides.
"One thing that makes this a predictably large bore tide is that we just had a full moon, and right now, the moon and the sun are in alignment," Lawson said.
Lawson said those gravitational forces work to pull the tide extremely negatively below what the average mean water level is at low tide.
"When the tide goes all the way out, the tide further up the arm is still going to be coming out when the new tide is coming in, and where those two bodies of water clash is where the wave is created," he said.
Local media had been alerting residents to the pending large bore tide since Monday.
"Today, everybody is telling us about it on the radio cause it's supposed to be a big bore tide," said Franklin, who drove from her home in Anchorage to see it.
There was no immediate measurement of the bore tide. The National Weather Service doesn't track it, and the state Department of Natural Resources and the National Oceanic and Atmospheric Administration didn't immediately have statistics Wednesday. The state department had earlier predicted it could be as tall as 49 inches, but Lawson said winds weren't conducive on Tuesday to help build a wave that large.
Nearly every space and places that weren't meant for parked cars were filled along the pullouts along the scenic Seward Highway. People brought lawn chairs, binoculars and cameras for the event.
Some climbed down the rocky beaches to outlying rocks for better viewing. That caused at least one problem, KTUU reported that three men became trapped on rocks after the tide came in and had to be rescued by a boat manned by the Anchorage Fire Department, which said the men were in no danger.
Several others, like Ives, donned their wet suits and tried to catch the wave.
Ives estimated her ride on the wave went anywhere from a quarter- to a half-mile.
"A nice long ride, long enough that my legs started to feel a little tired," she said.
She also wasn't bummed that this is apparently the largest bore tide of the summer, and plans to surf again.
"It just means that maybe next time there'll be fewer people out here, and it will be nice and quiet," she said.