Golf courses are covered in hazards — ponds, bunkers, thick rough — but here is another: the golf clubs themselves.

Scientists have determined that striking a rock while swinging a titanium club can create a shower of sparks that are hot enough, and last long enough, to start a brush fire.

The finding, by researchers at the University of California, Irvine, clears up what fire officials in Southern California have seen as a mystery: the origin of two recent golf course fires, including one that burned 25 acres and injured a firefighter in 2010.

Steve Concialdi, a captain with the Orange County Fire Authority, in Irvine, said that in both incidents, golfers using 3-irons with titanium-alloy heads had said they hit the ground and created sparks that started the fires.