Huntington Beach (US), Oct 9 (AP) A Southern California underwater oil pipeline was likely struck by an anchor several months to a year before a leak spilled tens of thousands of gallons of crude, the US Coast Guard has announced.

A large vessel of some kind may have struck the massive pipeline, shattering the concrete casing but not necessarily causing the slender crack from which oil spewed last weekend, said Capt. Jason Neubauer, chief of the Coast Guard's office of investigation and analysis.

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The longer timeline was partly based on marine growth that was spotted on the pipe in an underwater survey.

The pipe, which was found to be intact last October, may also have been struck several other times by other ships' anchors over the course of the period, he added.

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No ships have been identified, however.

"We're going to be looking at every vessel movement over that pipeline, and every close encroachment from the anchor just for the entire course of the year," the captain said.

The pipeline was dragged along the sea floor as much as 32 meters, Neubauer said.

That indicates a large vessel was involved, he said. Cargo ships with multiton anchors routinely move through the area from the ports of Los Angeles and Long Beach.

The leak fouled beaches and killed seabirds.

At least 17 accidents on pipelines carrying crude oil or other hazardous liquids have been linked to anchor strikes or suspected anchor strikes since 1986, according to an Associated Press review of more than 10,000 reports submitted to federal regulators.

According to federal records, in some cases an anchor strike is never conclusively proven, such as 2012 leak from an ExxonMobil pipeline in Louisiana's shallow Barataria Bay, where a direct strike by a barge or other boat also were considered possibilities.

In others the evidence of an anchor strike was obvious. During 1992's Hurricane Andrew, a 30,000-pound anchor was dragged by a drifting drilling rig over a Texaco pipeline in the Gulf of Mexico, causing a dent that broke open when the line was later re-started.

In 2003, a 7,000 pound anchor was found about 10 feet from a small spill on a Shell Oil pipeline in the Gulf.

A Coast Guard video released on Thursday appears to show a trench in the sandy seafloor leading to a bend in the submerged line, but experts offered varied opinions of the significance of the brief, grainy shots. An earlier video showcased a thin, 13-inch long rupture in the line.

Robert Bea, an engineering professor at the University of California, Berkeley and former Shell Oil engineer, said the second video appears to show a furrow in the seabed created by a dragging anchor leading to the damaged pipeline.

Investigators, however, are expected to consider other forces that could have moved and damaged the pipe, including water currents of movement in the seabed.

It will take time.

“The results from the analyses need to be validated -- corroborated. This process can bring even more questions,” Bea said.

"The shape of the crack indicates that it was caused by internal pressures in the pipeline. But, if that is true, why didn't the pipeline leak" earlier? Frank G. Adams, president of Houston-based Interface Consulting International, said in an email that the slight bow in the line displayed in one video “doesn't necessarily look like anchor damage.”

When a pipeline is hit by an anchor or other heavy object “that typically results in physical damage that may lead to a fracture,” he said.

Reports of a possible spill off Huntington Beach were first coming out Friday evening but the leak wasn't discovered until Saturday morning. While the size of the spill isn't known, the Coast Guard on Thursday slightly revised the parameters of the estimates to at least about 95,000 liters and no more than 500,000 liters.

The Coast Guard said about 20,819 liters of crude have been recovered from the ocean. The oil has spread southeast along the coast with reports of small amounts coming ashore in San Diego County, some 80.47 kilometers from the original site.

Local health officials said Friday that air samples from areas where oil potentially spread are within background levels — in other words, similar to air quality on a typical day — and below California health standards for the pollutants that were measured.

So far the impact on wildfire has been minimal — 10 dead birds and another 25 recovered alive and treated — but environmentalists caution the long-term impacts could be much greater. As cleanup continued on the shore, some beaches in Laguna Beach reopened Friday, though the public still can't go in the water.

Investigators are trying to determine what happened in the crucial early hours after reports of a possible oil spill first came in.

The narrow gash seen in one video could explain why signs of an oil slick were seen Friday night, but the spill eluded detection by the pipeline operator for more than 12 hours. (AP)

(The above story is verified and authored by Press Trust of India (PTI) staff. PTI, India’s premier news agency, employs more than 400 journalists and 500 stringers to cover almost every district and small town in India.. The views appearing in the above post do not reflect the opinions of LatestLY)