Kennicott Glacier Pulls the Plug on Hidden Creek Lake

Dennis Trabant saw a lake disappear this summer. Hidden Creek Lake near McCarthy vanished in late July, losing 10 billion gallons of water in two days. Trabant, a glaciologist with the U.S. Geological Survey, was part of a team studying the annual event that doubles the flow of the Kennicott River and moves more silt than 1,000 dump trucks.

The yearly draining of Hidden Creek Lake is what glaciologists call an outburst flood, when a body of water blocked by a glacier drains rapidly through a mysterious network of conduits beneath the glacier. Hidden Creek Lake is one of hundreds of Alaska creeks and rivers dammed by glaciers. Kennicott Glacier is the impressive plug to Hidden Creek, rising the height of a 20-story building to provide a wall that doesn’t leak until mid-summer.

When the lake leaves, the people of McCarthy and Kennicott notice. The bridge crossing to McCarthy over the Kennicott River is about 12 miles from Hidden Creek Lake; its waters have threatened the town and destroyed bridges for years. When the copper mines at Kennicott operated from about 1912 until 1938, officials of the Copper River and Northwestern Railway planned on building a new bridge every summer.

This predictability, along with eyewitness accounts of the flooding from 1911 to the present, made Hidden Creek Lake an attractive study area for a team that included Trabant, Andrew Fountain of Portland State University, and Suzanne Anderson of the University of California Santa Cruz. The researchers divided themselves into groups. Some camped near the lake to monitor its water level; others based in McCarthy monitored the Kennicott River at the footbridge. Trabant camped on a perch between the glacier and the lake. He and a colleague watched the lake longer than they expected before the action began.

“We knew it as Lake Won’t-Be-Gone,” Trabant said, referring to their five-week wait until they saw the first sign of Hidden Creek Lake’s draining.

On the afternoon of July 24, a floating marker showed that the lake had stopped rising, which was unusual because Hidden Creek was dumping glacial melt and rain into the lake at the same rate as it had earlier. In a few hours, Trabant noticed a “bathtub ring” around the lake basin. Icebergs from the glacier soon stopped floating, tilting as they rested on gravel. By the afternoon of July 27, the lake level dropped 320 feet.

As the water escaped, Kennicott Glacier started calving into the lake basin. Trabant watched as pinnacles of ice no longer supported by water crashed to the dry valley floor.

“It was an incredibly noisy place,” he said.

Twelve miles away, Suzanne Anderson measured the flow of the Kennicott River, which had swollen from 6,000 cubic feet per second to 15,000 cubic feet per second. Though the river was raging, the 2000 version of the flood was not as severe as the floods that took out railroad bridges in the past. Anderson said the river channel, inundated by the flood every year, has widened to handle the tremendous pulse of water.

After they churn through the data from their two-year study, the scientists hope to know more about the invisible processes beneath glaciers that allow these floods to occur. Hidden Creek Lake may get so deep that it floats part of Kennicott Glacier, prying the ice upward and opening a connection to channels underneath the glacier that have crept up from the river during the summer. Once the sub-glacier flood begins, it keeps the channels open until all the water is gone. Then, the incredible weight of the glacier seals them until the next summer, when the drama of Hidden Lake Creek plays out once again.