There were no injuries, but college spokesman Kevin Myers said Friday it will cost $2,000 to $3,000 to repair the building.
The incident happened last Saturday night following a rare trio of snowstorms in Portland.
Students started building the giant snowball on a campus quad near the dorm. Urged by a crowd, the math majors tried to make the snowball as big as possible by rolling it down the sidewalk that goes past the dorm.
"And the ball just got away from them," Myers said.
After escaping their control, the boulder-sized snowball rolled about 15 yards before slamming into Unit #7. Three students heard the smack and discovered the fractured bedroom wall. The student whose dorm was damaged has not had to move.
Nobody weighed the snowball, but a maintenance worker who sliced it up for removal estimated it to weigh 800 pounds or more, Myers said.
The students responsible for the runaway snowball reported the incident and won't be disciplined. Myers said they didn't intend to cause damage and feel awful about what happened. He declined to release their names and said he didn't know their class years.
Reed Magazine was first to report about the snowball.
"It was not the talk of campus until the story came out," Myers said. "The people that were there knew about it, but now it has kind of taken us by storm."