Above is the Ixtoc I oil well blowout after the oil platform Sedco 135 burned and sank in 1979.DCL


- The ongoing Gulf of Mexico oil well blowout is still not as big as the Ixtoc I leak in 1979.

- That spewed around 3.3 million barrels into the Gulf over 10.5 months before the well was capped.

- The environmental consequences of that spill were not as bad as they might have been.

Forty-two days into the worst oil spill in U.S. history, somewhere between 500,000 and 780,000 barrels of oil, possibly more, have contaminated the waters of the Gulf of Mexico.

But the ongoing Deepwater Horizon oil-well blowout is not the worst spill the Gulf has seen. The 1979 Ixtoc I well blowout spewed oil into Mexico's Bay of Campeche for 290 days, dumping around 3.3 million barrels of oil into the warm Gulf waters, as gas belching from below fed a continuous fire on the ocean's surface.

"The fire was so hot you couldn't face it, even at the distance we were, I suspect it was 100 yards," said Jerome Milman, retired professor at the Massachusetts Institute of Technology, who worked on stopping the Ixtoc I spill. "It would actually feel like it was burning the backs of your ears."

"That fire was a good thing," he noted, because it burned away the toxic gases, "except it prevented you from getting real close."

Compared to the 5,000-foot depth of the Deepwater Horizon spill, the Ixtoc I came from much shallower waters, about 160 feet, still within the reach of divers.

Otherwise, many of the circumstances were similar, with oil emerging from a broken pipe on the sea floor, and mixing with water and gas under high pressure to make goopy emulsions. Both blowouts followed the explosion and sinking of their respective drilling rigs. In both cases the blowout preventer failed.

Responders to Ixtoc I tried stopping the gush with a plug of metal balls, and with a giant "sombrero" placed over the well to capture the oil, much like the "junk shot" and containment dome attempted by BP. None of those methods worked.

Explore other devastating oil spill disasters through history, including the Ixtoc I.

The fact that the spill happened in warm offshore waters made the effects of the Ixtoc I spill less than they otherwise might have been, experts agreed. Warm temperatures accelerate the evaporation, weathering and microbes' consumption of oil. Much of the oil stayed offshore, evaporating or settling out on the sea floor.

"We were surprised there were so relatively few effects," said Olof Linden of the World Maritime University in Malmö, Sweden and part of a United Nations expert group that assessed the Ixtoc I spill.

There's a rule of thumb that for every 10 degrees Celsius increase in water temperature, chemical and biochemical reactions happen twice as quickly.

"That means if you compare the recovery time of the Exxon Valdez, where you had average temperatures of, say, 5 degrees, with those in the Mexican Gulf where the temperature is about 25 degrees, you have two doublings. What will happen in 20 years in Alaska will take five years in the Gulf," said Arne Jernelöv, who lead the U.N. team.

"The damage caused by the Ixtoc spill was huge," he wrote recently. "Beaches, mostly in Mexico but to some extent also in the United States, were hit, and birds succumbed in large numbers, despite the dispersion efforts. Because of the dispersion, shrimp, squid, and some fish populations suffered, with fisheries hit even harder."

The use of surface dispersants did help reduce bird kills, he said, but it took a heavier toll on small animals living in the water. Fish and octopus catches reportedly dropped by 50-70 percent that year from 1978 levels in some places, according to Jernelov and Linden's report. Fisheries in the area closed for a period, including the shrimp fishery, said Jernelöv, now of the Swedish Institute for Future Studies.

However, he said, "The much-reduced fishing pressure on fisheries that are normally over-fished meant that the fisheries' recovery went quite quickly. A few years down it was difficult to see any effect on the organisms. The damage the oil did was, to a significant extent, compensated or even overcompensated by the fact that you didn't have fishing."

Despite the similarities of the Ixtoc I and Deepwater Horizon spills, there is one major difference: wetlands. Linden said: "We didn't have the extensive wetland contamination we are talking about now."

Wetland contamination is difficult to reverse. As wetland plants' roots suffocate and degrade, the sediments they hold in place wash away, leaving nothing for new growth to anchor in. A few mangrove areas were lost in Ixtoc I.

"The oil hit sandy beaches mostly," Linden said, "and was therefore easier to clean up, though some of the cleanup in those days was not very carefully done."

Some oil on beaches was bulldozed under, but long stretches of beach were left alone where the oil weathered to tar and then to asphalt, said Jernelöv.

"Five years later, most of this was covered with sand," he added. "But where it was exposed, crabs were crawling over it and oysters and mussels were settled on it. The toxicity of it was gone. It looked like asphalt road."

The spill killed thousands of birds, Jernelöv said. "Maybe up to 10,000, which is a large number if you see them in one spot, but spread over a large distance. It was not like Exxon Valdez."

Researchers estimated 250,000 seabirds were killed by the Valdez spill.

By August 1979, oil reached the Texas shoreline, said Erich Gundlach, an independent consultant with E-tech International, Inc, who assessed shorelines and clean-up for Ixtoc I. "I never believed it would reach that far, but it did."

But a tropical storm did much to reduce that damage. "We had a tropical depression come in and raise the water level and it eroded the shore a little bit," Gundlach said. "It removed 80 percent of the oil that was on the shore of Texas."

Ixtoc I was was finally closed on March 23, 1980, by pumping mud into two relief wells drilled starting in June and July.

As huge as the Ixtoc I was, it was not the world's largest oil spill. The biggest one happened in Kuwait during the 1991 Gulf War when Iraqi forces dumped an estimated 6-8 million barrels of oil from tankers and oil terminals into the Persian Gulf, intending to set it on fire and thwart the U.S. military.