Rainforest GlacierI don’t know about you, but when I think about rainforests, I always think o

Rainforest GlacierI don’t know about you, but when I think about rainforests, I always think of Sean Connery, in “Medicine Man,” hunting for a bromeliad that holds a cure for cancer. An image that would never pop into my head is that of trekking through a rainforest in Alaska to see a glacier.Roughly the size of the U.S. state of West Virginia, Tongrass National Forest is the largest intact temperate rainforest in the world. It has been continuously inhabited for more than 10,000 years by grizzly bears, wolves, snowshoe hares, short-tailed weasels, bald eagles, Sitka black-tailed deer, and the native tribes of the Tlingit, Haida, and Tsimshian. Situated within the forest lies the 21 km (13 mi.) length of Mendenhall Glacier. Originally named Sitaantaagu (“the glacier behind the town”) by the Tlingit Indians, Mendenhall Glacier held several aliases before being renamed in 1892 for Thomas Corwin Mendenhall, who helped determine the boundary between Canada and the Alaska.Mendenhall glacier, part of the 3885 km (1500 sq. mi.) Juneau Icefield, is a remnant of the “little ice age” that began around 3000 years ago. Snowfall on the icefield has been known to exceed 31 m (100 ft.), reaching total depths of 62 m (200 ft.) in some years. The sheer weight and pressure of this accumulation changes the snow into glacial ice. The ice then gets pushed down the valley, gouging out and polishing the bedrock and dragging rocks and boulders of every size along with it, until it reaches its terminus at Mendenhall Lake (which only began to form around 1931) some 200-250 years later. The intense pressure causes the ice to become so dense that air bubbles that would reflect white light are pushed out of the crystalline matrix. As light penetrates the ice the longer wavelengths are absorbed and the shorter blue light waves are scattered and transmitted.In the mid-1700’s, around the same time the Industrial Revolution began, Mendenhall reached its point of maximum advance and began to retreat. Retreating at a rate of approximately 170 meters (558 ft.) per year, the terminus now rests 4 km (2.5 mi.) further down the valley. (See the Vimeo link below for images of the retreat.) Although seeds and spores were carried onto the newly exposed rock by wind and by animals, glacier debris is poor in nutrients. Nitrogen-fixing plants like lupines and alder paved the way for other growth. Eventually, spruce and hemlock filled in, creating the existing old growth forest. As you hike along the trail up to the glacier, signs along the way show the positions of the terminus over time. With prevailing climate conditions, the glacier will continue to retreat into the foreseeable future.Within the past few years, Mendenhall Glacier has provided a surprise for those who study it. Tree stumps and logs with roots and bark still attached have been appearing from beneath the retreating glacier, often in their original growth positions. From 1400-2000 years old, the trees from this reappearing forest are giving scientists a glimpse of a pre-glacial ecosystem.CWImage by the authorSourceshttp://www.fs.usda.gov/detail/tongass/about-foresthttp://1.usa.gov/1PxZN1Thttp://bit.ly/1VqVu95http://1.usa.gov/1MHVURBhttp://ak.audubon.org/tongass-national-forest-0http://www.livescience.com/39819-ancient-forest-thaws.htmlhhttp://bit.ly/1IF8OoRhttp://ngm.nationalgeographic.com/2007/07/tongass/chadwick-texthttps://vimeo.com/69802285http://www.britannica.com/place/Mendenhall-Glacierhttp://www.britannica.com/event/Industrial-Revolution -- source link
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