A glacier that periodically surges forward to dam a fjord, creating a temporary lake that floods when the ice dam breaks. The cycle creates and destroys ecosystems in dramatic flood-drought oscillations.
The galloping giant of Disenchantment Bay
Hubbard Glacier is North America's largest tidewater glacier, a 76-mile-long river of ice that flows from the slopes of Mount Logan in Canada to the Alaskan coast. Its terminus in Disenchantment Bay is over seven miles wide and its face stands roughly 350 feet above the waterline, with another 250 feet hidden below the surface. Unlike most glaciers worldwide, Hubbard has been steadily advancing since it was first mapped in 1895. This advance is not slow and steady; the glacier experiences surges, where it can move significantly faster than its usual pace.
This "galloping" behavior has consequences. The glacier's primary path of advance pushes it toward Gilbert Point, a narrow gap that connects Disenchantment Bay to the 35-mile-long Russell Fjord. On two recent occasions, in 1986 and 2002, the glacier surged forward enough to completely block this channel. It bulldozed a massive dam of ice and sediment, cutting the fjord off from the ocean and transforming it into a rapidly growing lake.
The 1986 closure began in May and lasted for nearly five months. Freshwater from melting ice and mountain streams poured into the newly formed "Russell Lake," causing its level to rise by as much as 25 meters (82 feet). The 2002 closure was shorter, lasting from June until August 14, when the dam—this time made more of pushed-up seafloor sediment called a moraine—gave way after the lake level reached 61 feet above sea level.
A cycle of flood and renewal
When the ice dam can no longer withstand the immense pressure of the rising lake, it fails catastrophically. On October 8, 1986, the dam burst. In the following 24 hours, an estimated 5.3 to 5.4 billion cubic meters of water erupted back into Disenchantment Bay. The resulting glacial outburst flood, known as a jökulhlaup, was the largest ever recorded in historical times, with a peak flow briefly estimated to be equivalent to 35 Niagara Falls.
This cycle of damming and flooding creates a unique and unstable environment. While the fjord is dammed, the influx of fresh water drastically lowers its salinity, trapping and killing marine life adapted to saltwater. If a future dam holds long enough, the water level in Russell Lake could rise high enough to overtop a low pass at its southern end. This would permanently reroute its outflow into the Situk River, a world-class salmon and steelhead fishery important to the nearby community of Yakutat. Such an event would increase the Situk's average flow by a factor of up to 50, scouring the riverbed and destroying the delicate ecosystem.
Scientists expect Hubbard Glacier to continue its advance. Future closures of Russell Fjord are not a matter of if, but when. Each event is a powerful natural experiment, showing the immense geological forces that continue to shape the Alaskan coast.
💡Fun Facts
The Tlingit name for the glacier is Sít' Tlein, which means "big glacier".
The ice at the glacier's face is up to 500 years old, originating as snow near Mount Logan.
During a surge, parts of the glacier have been recorded moving over 125 feet per hour, compared to a typical 3.5 feet per hour.
At its thickest points, the glacier is over 2,000 feet deep.
Accessible 24/7 as a natural feature, but only viewable via authorized boat or air tours.
Admission
Free to view, but access requires booking a cruise, boat tour, or flightseeing tour, typically from Yakutat.
Accessibility
The glacier face is only accessible by water or air. Tour boats provide viewing platforms, but the surrounding terrain is remote wilderness and not wheelchair accessible.