The Mendenhall Glacier’s recession is unveiling the remains of ancient forests that have remained frozen beneath the ice for up to 2,350 years.
UAS Professor of Geology and Environmental Science Program Coordinator Cathy Connor said she and others have been tracking the emergence of the forests’ remains. Some stumps and logs can be found in the moraines around the west side of the glacier. Some remain vertical, frozen to the ground in ice caves. Some are scoured smooth; some still have their bark. All are packed with silt in the outer layers.
As the glacier advanced, it snapped off the tops of the trees in its path, Connor said. The stumps were buried — and protected — in gravel.
Now, as the glacier melts, the melt water carves out paths in that gravel, revealing the remains of the trees.
The most recent stumps she’s dated emerging from the Mendenhall are between 1,400 and 1,200 years old. The oldest she’s tested are around 2,350 years old. She’s also dated some at around 1,870 to 2,000 years old.
“We’re seeing the Mendenhall wax and wane through time a little bit,” Connor said.
She anticipates the trees are spruce, although that hasn’t yet been scientifically verified.
At the end of the last glacial maximum, (the time at which glaciers were at their largest and most extended, about 20,000 years ago) before Southeast Alaska became the verdant place it is today, vegetation would have been more tundra-like, Connor said. The trees currently beneath the Mendenhall, however, shouldn’t differ significantly from those that grow around the glacier today.
Connor would like to find a deep pocket of sediment beneath the ice, potentially with more than one level of forest. Much of the rock around the Mendenhall Glacier is hard, meaning there are fewer layers of sediment, and fewer layers of history.
“The tricky part is, as the ice advances in earlier time, it tends to scour away whatever was there before,” she said. “So often you just get the latest chapter of the story, rather than come in at the introduction … It’s the luck of the Irish how you get a little bit of the story still remaining that hasn’t gotten ravaged and sent down the Mendenhall (River) and out to Gastineau Channel. Most of the story is now in the sea sediments and a little hard to decipher.”
In other areas of Southeast, tree remains tell stories about other glaciers.
“It’s an ongoing process,” said Professor Emeritus of Geophysics Roman Motyka. The recession of Eagle and Herbert glaciers is revealing trees of a similar age, he said.
In Glacier Bay, Connor and other researchers have found evidence of ice advances occurring more than 5,000 years ago. They’ve also documented the glacial advance between 1724 and 1794 A.D. that pushed Huna Tlingit off their land, and written a paper incorporating those cultural and geographic histories. In that paper they cite Tlingit histories recorded by Richard and Nora Dauenhauer as saying that glacier was growing and advancing “faster than a running dog.”
“It’s kind of cool that you have all these tree and sediment records that record what people have recorded in written and … oral history,” Connor said.
Today, the Taku Glacier is the only glacier of the 32 from the Juneau ice-field to be slowly advancing, pushing live cottonwoods out of the way. After the ice advance in the 1700s, most glaciers have been retreating, especially in the second half of the 20th century, Motyka said.
So far at the Mendenhall, the melting ice is only revealing trees.
“No sign of any 2,000-year-old personages, or flattened wolverines or any of that sort of thing,” Connor said. “No critters to report. No ancient climber … if there are any fossil ice people coming down the Mendenhall, I think they might have thawed and gone away since that time.”
Connor cautions those hiking near the glacier not to disturb the stumps.
“Those trees are newly thawing under the glacier for the first time in 2,000 years, which is kind of neat,” she said. “It’s like going to the tomb of King Tut or something like that. The tomb of the king spruce tree.”
• Contact Outdoors reporter Mary Catharine Martin at firstname.lastname@example.org.