UPDATE Friday at 2pm:
After weeks of trying to figure out what's blocking Bertha, the Washington Department of Transportation says a steel pipe is at least partly to blame for halting the Seattle tunnel project. And they knew it was there the whole time. Read more.
Students at Seattle's Thornton Creek Elementary were studying Washington State history when a mystery 60 feet under the city made their lessons very relevant to today.
"This fall we spent several months learning about the history of Seattle through the perspective of early settlers, like the Denny Party," says teacher Todd Bohannon.
His 5th graders were working through Thornton Creek's "expeditionary learning" program, which focuses on one thematic topic for the entire school year.
"We got to the point of the Great Seattle Fire, (and) the kids were extra excited about that because fire is exciting," Bohannon laughs, "There's this whole underground Seattle that you can't see because of the fire."
That's when one student brought in a newspaper clipping about engineers puzzling over an unknown object blocking the SR 99 tunneling machine known as Bertha. The drill has been stalled by a mysterious blockage under Seattle's waterfront since December 6th.
Twitter had been abuzz with guesses about what could be in Bertha's way. Mr. Bohannon knew he had to switch gears.
"It was at that point that I said ‘Oh, this is perfect.'" Bohannon scrapped the previously planned writing assignment, and the 5th graders got to work. "The kids had to come up with theories for what could be down there."
Early guesses were on the imaginative side. "A few kids wanted to go towards, ‘Perhaps there's an alien spacecraft down there.' But we tried to keep it focused on what we were learning."
Many immediately theorized there were remnants from the 1889 fire, which burned exceptionally hot, blocking the machine's progress.
"We had studied what Bertha could actually bore through. We don't think Bertha can actually bore through steel. That's when they came up with the idea that perhaps a train car or melted railroad lines had gone down and created a blob of steel that it can't get through."
Another popular guess: Saw blades left over from the early days of Seattle's lumber boom. "There were several mills down on the waterfront, including the Yesler mill. When they rebuilt the waterfront, a lot of that stuff was just left as fill."
The kids researched and brought in articles to support their guesses.
"Some of them were looking for big storms that would have sunk boats," explains Bohannon.
One student, Paden Grey uncovered the 1918 wreck of the A.J. Fuller, a ship that was converted to a floating cannery. It was struck by a steamer and sank in 10 minutes.
These 5th graders even drew from previous geology lessons, speculating that a glacial erratic was left from the last ice age.
What's an erratic? I had to look it up: A large piece of rock that differs from its native surroundings usually deposited by receding glaciers.
"There's actually a large erratic up in Wedgewood where I teach," said Mr. Bohannon.
Up next for these history sleuths?
Mr. Bohannon's 5th graders will go on the Seattle underground tour, and they are welcoming an expert on Bertha to talk about the big machine in their classroom.
"They're just as excited about Bertha, really, as they are about the ideas for what could be down there. Hopefully we will go down to the site where Bertha is stuck."
And Bohannon is even more convinced that learning is not a one-way street.
"They teach me all the time. All the time. And we learn together."
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