Southeast Alaska land rising as glaciers recede

Posted: Wednesday, September 06, 2000

SITKA (AP) --Southeast Alaska is growing, and scientists are puzzling out why and how fast the land at the northern end of the panhandle is emerging from the water.

Some of the uplift comes in areas recently uncovered by glaciers, such as the golf course Morgan Deboer operates on land his family homesteaded in Gustavus in the 1950s. As the glaciers recede, the land rebounds.

''Parts of the golf course that I used to hunt on in my teens ... was all mud and sand flat where you would hunt ducks,'' Deboer said. ''Now it's waist high in grasses willows and trees.''

Uplift has more than doubled the size the Deboer homestead. There is a question in Deboer's mind whether that trend will continue. It's a question geophysicist Roman Motyka may be able to help answer.

Motyka and his colleagues have placed about a dozen tide gauges from Lituya Bay to Sergius Narrows. The vertical position of each gauge is surveyed relative to a reference point on land.

After a period of weeks they return and collect data they hope will tell how high their reference points are above sea level.

''This very same thing was done back in 1959 and again in 1940,'' Motyka said. ''We'll compare our measurements with theirs to see how much shift there's been or how much uplift there's been relative to mean low water over that time interval.''

But glacial unloading, says Motyka, may not be the only factor contributing to uplift in Southeast Alaska.

The area is on a boundary where the North Pacific plate is sliding past the North American plate about six centimeters a year. Recent technology is helping the scientists get a handle on the horizontal movement of the earth's crust and whether it contributes to uplift. The global positioning system, or GPS, allows scientists to detect movements of less than a centimeter.

Another element of the project involves determining when the uplift episode began. That involves considering uplift in terms of centuries, rather than decades or years.

The biggest uplift in the region so far is in Excursion Inlet, where the land has risen about 20 feet since 1800, Motyka said.

The rates at which the land is emerging decrease toward the south, Motyka said. In Ketchikan they've only recently found indications that there's any uplift at all. Around Juneau the rate is about one and a half to two centimeters per year. In Glacier Bay and Yakutat it's about 4 centimeters annually.



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