Sean C. Morgan
Of The New Era
A boom heard throughout Sweet Home a little after 11 a.m. on Thursday, Jan. 5, was a small blast on Scott Mountain by Cascade Timber Consulting (CTC).
The explosion was intended to break up rock the company needed to move in a quarry, CTC officials said, but because the rock was on the surface, it caused a reverberation of sound that was reportedly felt and heard as far away as Cascadia.
A second blast on Friday went unheard by some while others reported hearing it faintly.
It was a smaller shot, and the cloud cover was higher on Friday, blaster Wayne Johnston said. The lower cloud cover on Thursday probably helped focus the sound on Sweet Home.
The blasts were near the top of Scott Mountain facing east toward Sweet Home.
“There were a few big rocks that were a little big to move with equipment,” CTC Road Supervisor Ben Masengil said. “That type of (blasting) operation is sometimes louder than others. It’s minimal compared to what we usually use.”
When blasting, “you don’t want it to be noisy,” Masengil said. “You want to break rock.”
Normally, explosive powder is poured into holes in the ground and covered with rock powder to help maximize the energy from the blast in breaking up rock. That also minimizes the sound from the explosion.
In the Thursday blast, CTC drilled holes into a rock and put less than 25 pounds of blasting powder into them, Masengil said. The result of the blast was that gases from the explosion escaped through cracks in the breaking rock and caused louder sound than normal blasting. The gases expand at better than 20,000 feet per second.
The sound actually represents energy from the blast, energy that is lost and not used to break up rock, Masengil said.
“It generates a lot of energy that moves into the atmosphere quickly,” Masengil said. “You lose a lot of the performance of the powder to the sound.”
Powder is expensive, so usually, translating energy to sound instead of breaking rocks is the last thing he wants to do, Masengil said.
CTC notified Linn County Sheriff’s Office, the Department of Forestry and other agencies because CTC officials expected there would be phone calls following the blast, Masengil said. “We just explained we were in an operation where we would generate sound.”
Sweet Home Police Department received a number of phone calls from citizens trying to find out what the sound was.
CTC also received a number of phone calls about the blast, Masengil said.
Blasting is a normal operation for CTC, Masengil said. The company blasts rock to use for road construction into logging operations.
CTC has used as much as eight tons of powder at once, but “you’ll never hear it” because the explosion occurs in the ground and the energy goes into breaking up the rock, Masengil said.
“If you contain it, you can use that energy. What we put off today probably wasn’t even 25 pounds,” he said.
Blasts heard in Sweet Home are rare, Masengil said. This blast was on top of Scott Mountain, away from homes.
Masegil said it would be preferable to get something into the newspaper ahead of blasts like this one, but noted that the logistics of setting up the shot, blocking roads, making sure the area is secure and scheduling contractors mean it is difficult to determine ahead of time exactly when the blast will occur.
The blast on Thursday drove Sweet Home residents out of buildings lining Main Street. Residents reported that it felt like a truck had driven into their building. One man in Cascadia reported that it knocked books from a shelf.
Talk around town about the source of the sound ranged from quarry blasting to a sonic boom.