One could tell it wasn't a normal water main break Thursday on First Avenue near Prospect Park by the absence of a pump - even as water poured in or out at a few hundred gallons a minute and the hole didn't fill up.
It didn't fill up because the water was plunging through loose rock at the bottom of the hole into a semi-legendary cavern, located at the junction of two -mile-long vertical fracture zones in the region's limestone and shale, according to a 1966 geological report.
The area is the scene of repeated line breaks, because of stress from subsidence, and Thursday's was right in front of an empty lot where workers in the mid-1960s razed a house after the front porch broke away and a deep crevice appeared in the basement.
Workers from a coal company sunk a 42-foot shaft to see what was underneath, according to a 1987 Mirror story on the plight of the owner of the razed house, who didn't receive compensation for his loss.
Workers placed a ladder in the shaft, but may not have located the bottom of the void, a city engineering employee told the Mirror at the time.
The manhole cover they placed over the shaft is still there, beneath 4 feet of asphalt on the sidewalk adjacent to the hole in the street workers dug Thursday, said Ray Dodson, assistant general manager of the Altoona Water Authority.
Mirror photo by J.D. Cavrich
Water gushes from a broken pipe in a sinkhole that opened up next to homes on First Avenue near 14th Street in Altoona on Thursday.
The asphalt is so thick because workers over the years have laid down layer upon layer to re-level the surface as it sunk.
Dodson wouldn't mind a peek into the presumed emptiness and said he planned to take advantage of the opportunity if the work led to uncovering the manhole entrance.
The void below the Prospect area owes its existence to rainwater percolating into the ground at the junction of the fractures for millions of years, dissolving the limestone, then washing away the remaining "interbedded" clay, geologist Laurence Lattman of State College wrote in his report to the city nearly 50 years ago.
The clay continues to erode, and there's no practical way to stop it, Lattman told officials at the time.
Because the erosion of the clay undermines utility pipes, the area is prone to water main leaks, which accelerate the washout, Lattman warned. The biggest danger is actually gas lines, which, if breached, create an explosion hazard, he wrote.
The authority learned of Thursday's break from a 1:30 a.m. phone call, after a resident realized his toilet tank wasn't refilling after a flush, Dodson said.
Workers with leak detection equipment located the break about 8 a.m., then dug open the street to expose the broken 4-inch main.
Gas company workers came to the scene because the authority workers' digging also exposed a 6-inch gas line, unsupported Thursday afternoon for a distance of about 8 feet.
Using a backhoe, workers hoisted and set aside a large slab of concrete that threatened to damage the gas line.
When standing in the hole, workers wore safety harnesses.
"I don't know whether the bottom might drop out," Dodson said.
Authority workers planned to fix the broken water pipe temporarily, then allow city highway workers to shore up the area underneath with concrete.
Authority workers then planned to fix the leak permanently by installing a new section of pipe and connecting it with the ends of the old pipe using sleeves and compression fittings.
Tom Beauchamp, who lives two doors north of the site of the razed house, worried about the stability of his residence and the house between his and the lot.
His parents own both structures, and they're remodeling the one next to the lot for his sister, who's getting married.
Travis Schaeffer, who lives on the other side of the lot, is also leery.
"The sidewalk has a funny looking dip," Schaeffer said. "We're parking our cars on next to nothing."
He alerted the authority workers who first arrived on scene Thursday to the existence of the cavern.
They were jackhammering, and realized Schaeffer knew what he was talking about when they poked a shovel in to the hole they'd created and found no resistance.
"They were like, 'Wow,'" Schaeffer said.