The wave is a tidal bore, a gravitational phenomenon that occurs when a full or new moon tugs at the tides, causing inlets like Turnagain Arm to empty into the bay even more than usual before sending water surging back toward shore. The bore is especially strong during the fall and spring equinoxes.
During the summer, surfers in Alaska take advantage of the inlet’s unusual water patterns. Though it’s somewhat dangerous, they trek across the mudflats with surfboards in tow. They then paddle out and hop on their boards to cruise atop the waves at speeds of up to 15 mph, set against a backdrop of snow-capped peaks.
You don’t have to be a surfer to enjoy the watery spectacle. Multiple spots along the road that winds along Turnagain Arm have vantage points that let you watch the wave from a distance. Keep an eye out for wildlife like harbor seals and beluga whales as well. On particularly cold days, the incoming bore churns the frozen salt water and sends large chunks of ice whirling through the inlet in a true show of nature’s strength.