About eight years ago, a group of hikers and scientists who had been hiking to the Herbert Glacier for years noticed something sticking out from the silt the glacier deposited as it retreated.
"When we first started going back there, Bob Garrison and I saw this ... material sticking out of the bank," said Al Shaw, an amateur geologist who has been hiking to the Herbert Glacier at least twice a year for many years. He and Garrison contacted their friend Mary Ann Parke, a geologist who was working with the Foundation for Glacier and Environmental Research, based at the University of Idaho.
Parke took samples of the trees and moss deposited by the glacier and had them dated by the radiocarbon method. The plants were 7,000 to 8,000 years old.
"It's fascinating to realize what's happened," said Parke, who also hikes to the glacier about twice a year.
What happened is that about 8,000 years ago, the Herbert Glacier retreated miles back in its valley, said Cathy Conner, a professor of earth sciences at the University of Alaska Southeast. She's been studying glaciers in Southeast Alaska for 20 years.
"The Herbert receded enough for a forest to grow, then it advanced and receded again, then advanced," Conner said.
The trees that were bulldozed in this series of advances and retreats are now lying at the end of the trail to the Herbert Glacier.
"When you emerge off the trail you're right alongside the river." Conner said. "You have to get yourself to where you can see where the river comes out from under the ice."
That's on the other side of the alder-covered rock on the left side of the glacier's face. To get to the 8,000-year-old trees, a hiker has to go up and over, or around, that rock.
"Wear rubber boots," Conner advises. The river can change in depth and course considerably from month to month.
Every year, scientists flock to Southeast Alaska to study the glaciers of the Juneau Icefield - the fifth largest icefield in the world. But Juneau residents don't have to be scientists to take an interest in the glaciers that wind down the valleys around town. Hiking to the Herbert Glacier on a regular basis can turn regular people into amateur scientists.
"Last year both the Mendenhall and Herbert (glaciers) do not appear to have changed between last fall and now," said Shaw, sounding as much like an expert on this particular area of Southeast Alaska as any geologist. He's been taking pictures of both glaciers in the fall and spring for several years, and makes a point of hiking with experts such as Parke and Conner.
Carolyn Gould, a Juneau resident who has been hiking to the Herbert Glacier since she was a Girl Scout in the 1950s, said that more than observing how the glacier has moved, she likes to note the changes in the course of the water that melts from the glacier.
"There used to be this very large waterfall coming down and at some point the water changed and the waterfall is gone," said Gould.
Topographic maps from the 1960s show a lake almost the size of the Mendenhall Lake in front of the Herbert Glacier, said Conner. Several years ago a lake drained that had formed on the glacier's east side next to an ice wall that created a dam.
Gould also likes to explore the terrain uncovered by the glacier as it retreats into the valley.
"It looks like a moonscape back there," she said. "There's nothing growing. There's just a lot of boulders."
A basic knowledge of glacier geology brings a new element to hiking the Herbert Glacier Trail.
"I would always encourage people to learn a little bit about the geology and glacial geology so they can see what is so beautifully exposed there," said Parke.
She recommends reading an introductory textbook on the subject or attending a geology class at UAS. This fall Conner will teach physical geology and geological history of life.
Parke recommends reading "After the Ice Age: The Return of Life to Glaciated North America" by E. C. Pielou.
"That's a tremendous read," she said. "It's an adult book, but one doesn't have to be particularly educated in sciences to read it. It's really quite interesting."
Shaw, who has gleaned his knowledge from books and through talking to scientists, said the reward comes in knowing what to look for and recognizing changes in the glaciers.
"The Herbert has been a very dramatic change in the last seven or eight years," Shaw said. "It's just sort of breathtaking to watch it change. All you can do is just sit there and say, 'Wow, this is really something.' "
Christine Schmid can be reached at email@example.com.