OAKLAND, Calif. -- Even the experts are having trouble explaining a solid block of ice that fell from the sky, crashed into earth and left behind a three-foot hole in the grass.

The ice fell at Bushrod Park in Oakland early Saturday when homeowner Jacek Purat of Berkeley was waiting nearby to show apartments to prospective renters.

"It was totally amazing. ... I saw this flash, like a streak. Then I saw this explosion, like a big boom! I came over and it (the field) was all covered with ice. Some were this big," Purat said, making a head-size circle with his two hands.

Brooks and Judith Mencher said they were standing on their back porch near the park when they heard a sound like a very loud rocket. "It kind of went 'whoosh!"' Brooks Mencher said.

The impact "knocked turf 20 feet away," according to Oakland Police Sgt. Ron Lighten. No one was injured.

Lt. Charles Glass of the Oakland Fire Hazardous Materials Team said the ice was pure water. "It didn't come from a toilet on a plane or anything like that."

Glass said the ice that firefighters pulled from the hole was about the same size of the hole -- three by three feet and two and a half feet deep.

Tony Hirsch, a Columbus, Ohio-based aviation expert, said ice falls of pure water are not uncommon: "Ice builds up on airplanes and falls off as they prepare to land."

But Hirsch said the airplane "would have to descend through what we call visible moisture, rain or clouds, for ice to build up." The skies were partly cloudy Saturday morning.

He said a large chunk of ice could build up on the vertical stabilizer or in a wheel well: "When they lower their landing gear, it falls off."

The National Weather Service said San Francisco Bay area storms haven't been violent enough to hatch a gigantic hailstone on its own. "There's nothing meteorological that would create a piece that big falling into Oakland," said weather service forecaster Diana Henderson.

It could simply be an unexplained "ice fall," one expert said. Big balls of ice sometimes fall from the sky without any real explanation.