Seldom does one find a way to directly date a prehistoric volcanic eruption, but 11-year-old Blake LaPerriere opened such a door for excited scientists in Southeast Alaska.
Last September, Blake, his parents, and his younger brothers were exploring a beach on southwestern Kruzof Island, part of the Tongass National Forest landscape and just west of Sitka, Alaska, where they live. Blake investigated a deeply incised creek behind a pile of beach drift where he found a standing burnt tree embedded in a tall bank of pumice. He brought it to his family’s attention, asking “Do you think that’s from a volcanic eruption a long time ago?”
Curious, Blake’s father Zach took photos and sent them my way.
As the forest’s geologist, it didn’t take me long to respond. Thanks to good weather, I was able to travel by boat to meet the family at the site the next weekend. Accompanied by Kitty LaBounty, assistant professor of natural sciences at University of Alaska Southeast, Deidra LaBounty, a geology student volunteer, and Jay Kinsman, a Forest Service geologist, we examined the site.
We carefully documented what we found, sending samples of the wood from the embedded tree to a lab for radiocarbon dating and to the University of Oregon for identification. First, we learned that the tree was indeed ancient – dating back 13,180 years. Then, Jamie Dexter from the University of Oregon confirmed the tree as Picea sitchensis, or Sitka spruce, making this one of the oldest records of Sitka spruce in Southeastern Alaska.
After I gave Blake the news on the age and identification of his find, I explained how the tree came to be there.
Southern Kruzof Island consists of more than a dozen volcanic vents and domes referred to as the Mount Edgecumbe Volcanic Field. Mount Edgecumbe dominates the landscape rising to more than 3,200 feet. Its symmetric cone and crater create a striking image. The field first erupted approximately 600,000 years ago, with volcanic activity continuing until 5,000 to 6,000 years ago.
About 13,180 years ago, a violent eruption on Crater Ridge just north of Mount Edgecumbe resulted in deep deposits of rhyolitic airfall, what we know as pumice and ash, and pyroclastic flows or fluidized rock fragments and hot gases. These fast moving flows swept down from the saddle between Crater Ridge and Mount Edgecumbe, rapidly burying the forest and vegetation on the lower slopes.
Blake had discovered one of these trees.
Knowing the tree’s age helps scientists establish the age of the simultaneous eruptions which spread ash across much of Southeast Alaska.
Interestingly, at the time of the eruption that encased the Kruzof tree, global sea levels were about 174 feet lower than today. The lands west of Sitka were a coastal plane with fresh water lakes.
The Kruzof tree is a record of an established forest in what was likely a refugium – a place where plants and animals persisted during the last ice age. This preserved relic gives us a small snapshot into the timing and extent of glaciation, the prehistoric climate, and the possibility of refugia where other plant and animals persisted and early migrants to North America may have passed. About 250 years after the eruption that trapped the tree, rising sea levels inundated the coastal plane and fresh water lakes creating Sitka Sound.
My plan is to return to the area in the future to see if other trees emerge as waves erode the bank. I’ll be looking for evidence of the soil and vegetation, which must be buried beneath the pumice flow.
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Wow, Blake - great find! You're quite a hero.
This is very interesting and exciting to read about. I grew up in Sitka and I'm excited that we have such a historic database right in our front yard. Hope more trees are discovered.
Great example of "citizen science" in action -- congrats, Blake, for being so observant, and thanks to Dr. Baichtal for making Blake's day in how he engaged with the young man and conveyed the excitement of the discovery process, science, and the methods used to unravel the mystery.
How interesting! There are still many things to find and young people are looking and learning> How great is that!!
This is the kind of thing that needs to be made available to more children. The CORE idea is not the answer. The maintenance of a stable , encouraging family unit is the answer. A woman on welfare with four kids by different fathers is dumbing down our country. There isn't an adult out there that can't volunteer and help. I've spent many years with to Boy Scouts. Others can pick an area they want. This young guy is never going to forget his experience in the outdoors and neither will his friends! They all have this step up on those that sit and play computer games. It all begins at home.
So glad to see kids learning about the geology of SE AK!!! Jim is a great teacher and I'm thankful daily for what I learned from him when I was still in school in SE AK :) It's always great to see new stories from home.
Cool Blake! Just imagine at that time the ocean was so low you could walk back to Sitka around freshwater lakes. I wonder if there were people here then?
thank you both
Great find! On another note, do the many bubbles in the coves come from geo-thermal activity below?
@Wendy - thank you for your question. There is no known geothermal activity on Kruzof Island. The highly dissected coastline is the result of wave action stripping the pyroclastic flow off of the 313,000-year-old lava flow beneath. If you are referring to the iron staining of the pyroclastic flow (the red banding), that is likely groundwater redepositing iron adjacent to the tree that acts as a preferential flow path.