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09.06.2000
位於阿拉斯加東南區域的Sitka正在逐漸上升當中，而科學家們正試著找出造成上升的原因，並嘗試推算在Panhandle北端地表浮出水面的速率有多快。
某些上升的情形發生在冰河剛消退的區域，如Morgan Deboer 於1950年代所經營屬於其家產的高爾夫球場就是一個例子。
Deboer說：「高爾夫球場部分的區域是我在十幾歲時常去打獵的地方….這些可以讓你獵到野鴨的地方全都是泥濘及平坦的沙地」「現在則長滿了禾本科的柳樹及其他樹木」。
上升土地的面積已經超過Deboer家產的兩倍，Deboer心中有個關於這樣的趨勢是否會持續下去的疑問，而這個疑問也許能由地球物理學家Roman Motyka來幫他解答。
Motyka及他的同事在Lituya灣到Sergius海峽之間設置了十幾個潮汐測量器，所獲得的每一個垂直位置的測量值均會與位於陸地上的某個參考點作比較。
經過數週之後，他們回到設置測量器的地點並蒐集測量資料，希望能藉由這些測量值來究明他們所設置的參考點到底高出海平面多少。
Mityka說：「一模一樣的研究早在1940年就做過了，並且在1959年又再做了一次」「我們將會拿我們得出的結果與他們的做一個比較，以便知道這個區域在經過這些年以後，與平均低潮位相較，到底是移動或是上升了多少」。
不過，據Motyka表示，也許冰河消退並非是造成阿拉斯加東南區域上升的唯一原因。
這塊區域恰巧是位於北太平洋板塊與北美板塊互相交錯的邊界上，平均每年的移動距離大約是六公分。現代的科技能幫助科學家了解地球板塊的水平移動，及是否為造成地表上升的原因。
簡稱為GPS的全球定位系統能讓科學家偵測到小於一公分的移動。
在這項計劃當中尚且包含了另一項主題，就是這樣的上升情形是從何時開始的，這必須考慮到近百年來的情形，而不只是近幾十年或是近幾年而已。
Motyka表示，在這個區域中上升最多的地方是Excursion Inlet，自1800年以大約上升了20英呎之多。
Motyka說，土地上升的速率隨著越往南方而遞減。最近在Ketchikan發現已經沒有上升的情形發生，而在Juneau附近的上升速率大約是每年1.5公分到2公分，在Glacier灣則是有每年4公分的上升速率。
全文及圖示詳見: http://www.adn.com/metro/story/0,2633,192323,00.html
版權歸屬 Ecotrust Website 環境信託基金會 (陳均輝譯，林子倫 審校)
中英對照全文：http://news.ngo.org.tw/issue/climate/sub-cc00091901.htm
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Published September 6, 2000
Sitka -- 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 of 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 11/2 to 2 centimeters per year. In Glacier Bay and Yakutat it's about 4 centimeters annually.
http://www.adn.com/metro/story/0,2633,192323,00.html
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