Some astonished visitors to Annadel State Park say they're grateful they weren't hit and killed when two large chunks of ice fell from a cloudless sky.

"They were coming down like bullets," said mountain biker Ron Schuelke, an economics instructor at Santa Rosa Junior College. "I've never heard of anything like this in my life."

As the white chunks plummeted and struck with distinct thuds Tuesday near the east Santa Rosa park's Lake Ilsanjo, both Schuelke and a second cyclist, Ryan O'Harren, were resting on the dam. O'Harren said the objects slammed into the ground close enough to him, Schuelke and four women hikers at a nearby picnic table to count as scary.

After the second impact, he suggested to Schuelke, whom he didn't know, that he put his helmet back on. Schuelke did.

The JC instructor had only heard the falling objects, but O'Harren said he heard them -#8212; the sound was similar to that of a kite being yanked strongly from the sky, he said -#8212; and saw them. He said both were white and while he didn't get good enough a view of the first to judge its size, the second appeared about as big as a volleyball.

O'Harren estimates that the first object crashed through trees and struck the Earth about 200 feet from him and the second, seconds later, struck about 100 feet away.

All six of the witnesses went looking for whatever it was that had rained like meteorites. Their discoveries had them shaking their heads.

Schuelke said the first object they found was "a large chunk of ice that had indented the ground and broken into smaller chunks."

"I guess its size to be approximately 18 inches across and maybe two to three inches deep," he said.

"I found the second, smaller chunk on the other side of Spring Creek Trail. It was about four to five inches long and two to three inches deep."

Photos that he and Schuelke snapped show the chunks to be the color of dirty snow. One has a large hole through it.

The cyclists said separately they're quite certain that had they or any of the four women been struck by the chunks, the impact could easily have killed them.

So where did they come from?

Both O'Harren and Schuelke searched the Internet and found that the possibilities include naturally occurring atmospheric ice conglomerations called megacryometeors, and frozen wastewater that falls off jetliners.

Coincidentally, O'Harren is a pilot with JetBlue.

He's aware that some people mistakenly believe that commercial jetliners still release their toilet flushings into the atmosphere. Leaks in aircraft toilets can cause ice bombs, but those are tinted the deep blue of an aviation toilet's liquid disinfectant.

O'Harren said that through the course of his 17 years as pilot he has heard tales of ice forming from the greywater that drains from a jetliner's sinks and galleys, and that is released midair from a heated line on the underside of the plane.

The release pipe has to be kept quite warm because the temperature at a cruising altitude of 30,000 or 40,000 feet is far below 0 degrees Fahrenheit.

A photographer as well as a pilot, O'Harren suggested on his Website, www.ryanoharrenphotography.com, that perhaps the hole in the intact Annadel chunk "is from the drain mast of an airplane that passed overhead; the heating element on the mast may have failed resulting in sink water to instantly freeze around it.

"Naturally, when it became too heavy, or as the plane descended into warmer air, it just fell off," O'Harren wrote.

Told of the icebombs and shown O'Harren's photos, veteran pilot Don Pedrazzini of Santa Rosa said he is certain the ice formed from water that drained from the sinks and/or galleys of a jetliner or large military aircraft.

"Look at the pictures and you can see where it formed around something that was pointed," said Pedrazzini, who flew in Vietnam and then 33 years for Delta Airlines.

"It is very white in color, so it is not from a leaking toilet," he said.

Pedrazzini recalled that years ago, he received a bulletin alerting pilots who flew into Tokyo that a village beneath the trans-Pacific approach was being hit by chunks of ice falling from jetliners. He said pilots were instructed to lower their landing gear earlier, so that any ice shaken loose would fall into the ocean.

O'Harren notes in his blog that Lake Ilsanjo is located directly beneath an approach to Oakland International Airport. He wrote that a "quick review on FlightAware," an online flight tracking service, revealed "there was a Southwest Boeing 737-700 from Portland, OR, to Oakland that flew directly overhead on this route near the time of the ice fall."

Both O'Harren and Schuelke suspect they may never know for sure where the great, frozen chunks came from. But they're certain of this: They're mighty glad no one was hit in the head.

You can reach Staff Writer Chris Smith at 521-5211 or chris.smith@pressdemocrat.com.