Three brush fires in the Back Bay Fens near Kerr Hall caused dense clouds of smoke and lingering ash to settle throughout the neighborhood on Monday.

The first fire was reported at 3:54 p.m., the second at 10:50 p.m. and the third shortly after 11 p.m., according to a Boston Fire Department spokesman.

Three fire engines and two ladder trucks responded to the half-acre blaze, which took fire fighters about an hour to put out, the spokesman said.

By the next day, the cause of the fires was still unknown, but not a pressing concern, and no one was injured.

“It’s a yearly tradition,” the spokesman said. “It gets so dry down there that something happens and it just burns, but it’ll still be as tall and as thick next year.”

The passing sirens and lingering smoke was enough to draw more than 100 students to the scene, said Sarah Lawson, a freshman physical therapy major.

Lawson arrived at the fire just before 11 p.m., seeing flames shoot as high as 30 feet, she said, adding that fire fighters seemed to have the fire under control.

“Everyone was just gathering around, taking pictures and watching the fire fighters put it out,” she said.

Freshman physical therapy major Mary Woods had a similar experience.

“I was walking back to my dorm with a friend, and we saw ash falling from the sky, so we wanted to see where it was coming from,” she said.

Freshman linguistics major Rebecca Collins said she could smell smoke from her residence in White Hall, but was relieved that it was not started there.

“At first, I thought it was just someone burning something in my room, but then one of my friends called and told me what happened,” she said.