Alaska Glaciers Melt, But Land Rises

Photo by Michael Penn for The New York Times

In Juneau, Alaska, as the glaciers continue to melt, the land is actually rising. At a rate of 10 feet in the last 200 years, the melting is depositing so much sediment that local streams are drying up and having an effect on the salmon and many local ecosystems.

The geology is complex, but it boils down to this: relieved of billions of tons of glacial weight, the land has risen much like a couch cushion regains its shape after someone gets up from their seat. The land is ascending so fast that the rising seas — a ubiquitous byproduct of global warming — cannot keep pace. As a result, the relative sea level is falling, at a rate "among the highest ever recorded," according to a 2007 report by a panel of experts convened by Bruce Botelho, Juneau's mayor.

In some places along the coast, the change has been so rapid that kayakers whose charts are not up-to-the-minute can find themselves carrying their boats over shoals that are so high and dry they support grass or even small trees.

A few decades ago, large boats could sail regularly along Gastineau Channel between downtown Juneau and Douglas Island, to Auke Bay, a port about 10 miles to the northwest. Today, much of the channel is exposed mud flat at low tide. "There is so much sediment coming in from the Mendenhall Glacier and the rivers — it has basically silted in," said Bruce Molnia, a geologist at the U.S. Geological Survey who studies Alaskan glaciers. "The land is rising almost three inches a year", Molnia said, making it "the fastest-rising place in North America."

The rise is further fueled by the movement of the tectonic plates that form the Earth's crust. As the Pacific plate pushes under the North American plate, Juneau and its hilly Tongass National Forest environs rise still more. "When you combine tectonics and glacial readjustment, you get rates that are incomprehensible", Molnia said.

Source - New York Times