Predicting how a disaster will unfold is slippery at best—especially when the event is unprecedented, facts are thin on the ground, and some variables simply stack up to luck.
The Gulf oil spill was no exception, and many unexpected developments—from the Gulf economy taking a huge hit to oil getting trapped in the cold depths—foiled many an expert prediction.
A year later, here's a look at some of the major surprises from the spill.
(Read more stories about the Gulf oil spill anniversary.)
East Coast Stayed Oil-Free
When nearly five million barrels of oil gushed into the Gulf of Mexico (map) last year, experts warned that some of that crude could be headed around the tip of Florida and straight up the East Coast, courtesy of the strong Gulf Loop Current that threatened to carry oil into the Gulf Stream.
Though some oil did end up in the Loop Current, the oil never made it up the East Coast.
But that doesn't mean the same scenario couldn't or wouldn't unfold with any future spill in the area, according to physical oceanographer Robert Weisberg of the University of South Florida in Tampa.
"As the loop current migrated north towards the wellhead, it broke off an eddy which in essence severed contact from the area of the spill to the Florida Keys," Weisberg said. "That was a good thing. Florida lucked out, and so did the nation, really."
But the Loop Current is an ever-changing entity. If the Gulf oil spill had happened now, for instance, things might have turned out quite differently.
"Today the Loop Current is extending almost as far north as the wellhead, and it regularly makes its way that far north. If the same spill was to happen right now, those fears [of oil in the Gulf Stream] would probably be fulfilled," Weisberg said.
Weisberg stressed that the threat of Loop Current oil heading up the East Coast remains a concern for future operations in the Gulf, and especially those south of U.S. waters.
"Cuba is claiming that they are going to be drilling in areas that the loop regularly passes through," he said. "If an issue occurred in the middle of the Florida Straits, off northwest Cuba, then there would be plenty of oil going up the East Coast of the U.S."
"Black Tide" Didn't Inundate Coasts
Due to the spill's deepwater origin and some fortuitous calm weather, most Gulf Coast beaches and wetlands escaped the kind of catastrophic oiling that many had feared. (See pictures: "Heavy Oil Seeping Into Louisiana Marshes.")
"Certainly the impact on wetlands is not anything like it could have been," said Larry McKinney, director of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University in Corpus Christi.
"In the short term it looks like the system was resilient enough to withstand this, and you also have to give some credit to the response that may have minimized that impact by efforts to skim and burn and boom and use dispersants."
Also key is that the spill originated 1 mile (1.6 kilometers) below the surface, rather than on the surface like the Exxon Valdez disaster, said Edward Overton, professor emeritus of environmental sciences at Louisiana State University (LSU).
That means much of the oil never made it to the surface at all, and instead spread throughout Gulf waters. (See "Toxic Oil Found Deep on Gulf Seafloor?")
"Valdez was a massive black tide on the surface and the winds pushed that black tide ashore," Overton said. "That didn't happen in this case. And that surprised some people, but folks who understand oil spills knew they were dealing with a different beast."
The reach of the oil on the surface was further minimized by good weather. Ill-timed or directed storms could have driven far more of the oil ashore. (Related: "Hurricanes May Be Good for Gulf Oil Spill, Experts Say.")
Harte Research Institute's McKinney, a biologist by training, cautioned that while acute coastal damage appears to be less than many feared, it could be years before less obvious impacts become apparent.
Overton agreed. "We're just now getting through that first growing cycle," he said. "We don't know the impacts we're going to see, and undoubtedly there will be some impacts over the next couple of years. But I'm more relieved than I thought I would be a year ago at this time, to tell you the truth."
"Except in the most heavily oiled areas, we're starting to see some plants growing back through and a kind of green ring along oiled coastline with shoots coming up through. That's a very encouraging sign," Overton said.
But some areas—especially hard-to-clean marshes—are still awash in the black goo. (Read about Louisiana's oil-soaked wetlands in National Geographic magazine [October 2010].)
"All of the oil that did reach shore is going to be there for a long while because it's trapped in the sediments," said Terry Hazen, a microbial ecologist at the U.S. Department of Energy's Lawrence Berkeley National Laboratory in Berkeley, California. There could be a long-term threat to people and animals who dig into the oiled sand or encounter oil that's newly churned up from future storms.
Hazen added that there's little that can be done about such oil at this point. "Once it's buried deep enough . . . the best thing to do is leave it alone," he said.
"The deeper it gets, the less risk it represents, and it will get gradually deeper. We just don't know how fast."
Fisheries Weren't Destroyed
Fishing is an economic mainstay and a way of life in the Gulf, and the spill spawned fears that the industry might be damaged for years. In terms of fishery production, those fears so far appear to have been largely unfounded, Harte Research Institute's McKinney said.
"I was happy to see that a lot of the concerns we had about impacts on fisheries like shrimp and crabs and those types of things, it's looking like they may be minimal, at least initially," he said.
(Watch video: "Oil Inside Gulf Crabs May Be Shed.")
"The sampling that's taking place right now, while spawning is going on in the spring, will give us a better read to see if there is going to be any significant decrease in the production of seafood, but indications are that we will not see that impact."
Oysters were hit hard last year by both the Gulf oil spill and by oil-fighting measures, such as freshwater flooding, meant to keep oil out of bays and estuaries. Despite this blow, many Gulf oyster beds are slowly rebounding and some oysters have reappeared on Gulf menus.
While productive fisheries would be a major boon to many on the Gulf Coast, McKinney warns that there may yet be unseen consequences of the oil.
"We may see that some of the long-term, underlying effects of the spill could be covered up," he said.
"Species like shrimp and crabs are almost like weeds—they can live under almost any conditions and do well, and they are so spread out across the Gulf that they can quickly fill in the gaps [where oil damage occurred] and perhaps swamp them.
"Sometimes you can get a false impression that we've recovered, but the internal damage is what we need to look at now."
Gulf Economy Hit Harder Than Thought
In a region still reeling from Hurricane Katrina, the Gulf oil spill was a heavy blow that left fishers stranded ashore for months and hotel rooms and restaurants empty. Though these dire straits came as no surprise, McKinney said, the impacts have been even worse than many people anticipated.
The sudden shutdown of so many local industries left many families without income, pushing some to the brink of economic disaster. Demand for seafood is still down due to false perceptions that seafood is unsafe, he added.
(Watch video: "Oil Spill Threatens Native American 'Water' Village.")
"We probably underestimated the economic consequences of this spill," he said. "It's difficult to understand until you actually see it in the faces of the people who live along the coast. There's no doubt the economic impacts of this thing are still with us and are certainly severe."
In fact, McKinney said, one can make a case that the spill's economic consequences outweigh its environmental impacts.
"The repercussions of this are really clear," he added. "It makes the case that a healthy environment is good for the economy and an unhealthy one is bad for the economy."
Mother Nature Cleaned Up Oil Quickly
Scientists were also surprised by the speed by which nature cleaned up some aspects of the spill. In just four months, enormous bacterial blooms ate much of the methane that roared into the Gulf along with oil—far faster than anyone would have predicted.
Methane is a main component of natural gas often found with oil, and in the Gulf oil spill made up 20 percent of the total flow from the wellhead.
"We knew these guys were there," said John Kessler, a chemical oceanographer at Texas A&M University. "What surprised us was how quickly they consumed methane. Normally we see much slower rates, but then again normally we see methane concentrations [from natural seeps] that are 10,000 to 100,000 times lower than here," he added.
(Read more about how nature is fighting back against the oil spill.)
Because the Gulf spill emitted more methane than any other compound, Kessler refers to the BP disaster as more a methane spill than anything else.
In addition, although Mother Nature seemed to clean up our mess this time, Kessler cautions that she won't always do so in other regions of the world.
That's because the Gulf of Mexico's unique environment likely harbors especially efficient methane-eaters that dine on what's released from natural seeps. The Gulf's relatively warm water temperatures may have also helped bacteria populations grow.
"This was very encouraging for the Gulf, but it also tells us that we don't fully understand the process or what the ultimate biological limitations might be for these bacteria," Kessler said.
"What can they clean up and how quickly can they do it? Is there any way to enhance these rates?"
Oil Got Stuck in Deepwater "Refrigerator"
When the vast amounts of oil gushed into the deep Gulf, it created a unique, real-time experiment in the mixing of oil and water that kept more oil trapped underwater than scientists had foreseen. (See "Giant Underwater Plume Confirmed—Gulf Oil Not Degrading.")
"And that deepwater oil isn't going anywhere," Harte Research Institute's McKinney said. "It's sitting in a refrigerator and it's going to be there a long time."
"It should have been more clear at the time, but it was a very frantic time," LSU's Overton added.
When oil is released at depth, Overton explained, there will be some type of plume from the release point to the surface—but how oil behaves in the plume is subject to a number of variables.
"Big thick globs, like a tennis ball, come up in five or six hours," he said. "If it's the size of a pea or grain of sand, it may take tens or hundreds of hours to come up. And if it's underwater for say a hundred hours, the currents are going to move it.
"Of course the thing that I think surprised a lot of people, including myself, is that oil dispersed into really tiny particles, [smaller than] the size of a human hair, never gets to the surface. It stays down and is moved by currents and dispersed and diluted in the Gulf. I'm hearing numbers that maybe 50 percent of that oil never got to the surface."
This mixing process means that a lot less oil ended up as visible surface slicks or reached beaches and wetlands.
That's good news, but determining what all that oil means for offshore Gulf waters and seafloor ecosystems is a big challenge.
(See an interactive of the Gulf's layers of life in National Geographic magazine.)
"I think the deep ocean is where the consequences of the spill are going to be most manifest," Harte Research Institute's McKinney said. "And that's a place where it's very difficult for us to see them."
Hazen and colleagues have found that some cold-loving bacteria degraded a lot of the deep oil—although some low concentrations may remain.
Gulf Can't be Put in MRI
Overall, it's simply too early to say what the true state of the Gulf is right now, noted Christopher Reddy, director of the Woods Hole Oceanographic Institution's Coastal Ocean Institute.
"Visually it looks pretty good if you flew over in a helicopter," he said.
"But I think one of the problems is that, despite great sampling efforts, we just can't put the Gulf of Mexico in an MRI.
"And even if we could, you wouldn't get the results back in a couple of days—or even by the one-year anniversary."