The devastating flooding that occurred along the Yellowstone River last week constitutes a 1 in 500-year event, according to a U.S. Geological Survey (USGS) news release.

Unprecedented rain and rapid snowmelt in recent days have caused rivers in parts of Montana, Wyoming, and Idaho to burst their banks, swallowing bridges and sweeping away entire sections of roadway.

More than 10,000 visitors to Yellowstone National Park have been forced to evacuate. All entrances to the park are expected to remain closed until at least Monday.

"At two streamgages, Yellowstone River at Corwin Springs and Yellowstone River at Livingston, the peak streamflow was higher than the 0.2% (or 1 in 500-years) flood (level)," said USGS hydrologist Katherine Chase in the release.

Farther downstream, "the Yellowstone River at Billings was between the 1% (or 1 in 100-years) and 0.2% (1 in 500-years) flood," according to the release, which notes that streamflow data is "currently being reported as 'provisional' until follow up analyses of the stream channel and data are completed."

However, Chase notes in the release that, "while these floods are often referred to as greater than (or rarer than) a 1 in 500-year event, there is the same probability that they could occur in any given year."

The USGS frequencies are calculated from historical data for the Yellowstone River's locations. As CNN has reported last week, scientists have shown that climate change is impacting the frequency at which extreme weather events occur, and that trend is expected to continue as the planet continues to warm.

In a three-day period last week, Yellowstone National Park received about two to three times the typical rainfall for the whole month of June, and precipitation this month has already been more than 400% of the average across northwestern Wyoming and southern Montana, according to the National Weather Service.

Video: Couple describes moment home was swept into Yellowstone River

Yellowstone south loop to reopen

All five of Yellowstone's park entrances remained closed Friday as flood recovery and repair efforts are underway in preparation for the park's reopening, according to a release from the park's superintendent's office.

According to the release, the National Park Service does not yet have an estimated reopening date for the entire park -- nor an idea of total repair costs. The release outlines an extensive list of needed repairs to roads and infrastructure in each section of the park in order for it to reopen.

"We have made tremendous progress in a very short amount of time but have a long way to go," Superintendent Cam Sholly said in the release. "All emergency and life safety objectives within the park have been accomplished or stabilized within the first 96 hours of the flood event, without major injury or death."

The park service announced on Saturday the south loop of the park will reopen to the public on Wednesday.

"At 8 a.m. Wednesday, June 22, Yellowstone National Park will begin allowing visitors to access the south loop of the park," according to a news release from Yellowstone National Park. "The south loop is accessed from the East (Cody), West (West Yellowstone), and South (Grand Teton/Jackson). Areas accessible include Madison, Old Faithful, Grant Village, Lake Village, Canyon Village and Norris."

Backcountry areas accessible from roads open to the public will be available for day use only, according to the release. Overnight use from trailheads in the south will open on July 1.

While the north loop is closed, "park staff have engaged over 1,000 business owners, park partners, commercial operators and residents in surrounding gateway communities to determine how to manage summer visitation," the park service said.

Video: Yellowstone River flooding aerials

To ensure the south loop does not become overwhelmed by visitors and to balance the demand for visitor access, the park will institute an interim visitor access plan," according to the release.

"The interim plan, referred to as the Alternating License Plate System (ALPS), was suggested as a solution by gateway communities during major public engagement with the park this past week," the release read.

Montana Gov. Greg Gianforte struck an optimistic tone about flood recovery and rebuilding as he encouraged continued tourism to the Big Sky State. The "best days are ahead of us," he told reporters Friday.

"We're open. You've got to come," Gianforte said of Yellowstone Park. "The vitality of our communities depends on it. We're open for business, and we want you to come."

Officials have previously said the northern section of the park will likely remain closed through the remainder of the season.

FROMBERG, Mont. —

As officials scramble to reopen Yellowstone National Park to tourists after record floods pounded southern Montana, some of those hardest hit in the disaster live far from the famous park's limelight and are leaning heavily on one another to pull their lives out of the mud.

In and around the agricultural community of Fromberg, the Clarks Fork River flooded almost 100 homes and badly damaged a major irrigation ditch that serves many farms. The town's mayor says about a third of the flooded homes are too far gone to be repaired.

Video above: Officials seek quick Yellowstone flooding repairs

Not far from the riverbank, Lindi O'Brien's trailer home was raised high enough to avoid major damage. But she got water in her barns and sheds, lost some of her poultry and saw her recently deceased parents' home get swamped with several feet of water.

Elected officials who showed up to tour the damage in Red Lodge and Gardiner — Montana tourist towns that serve as gateways to Yellowstone — haven't made it to Fromberg to see its devastation. O'Brien said the lack of attention is no surprise given the town's location away from major tourist routes.

She said she's not resentful but resigned to the idea that if Fromberg is going to recover, its roughly 400 residents will have to do much of the work themselves.

"We take care of each other," O'Brien said as she and two longtime friends, Melody Murter and Aileen Rogers, combed through mud-caked items scattered across her property. O'Brien, an art teacher for the local school, had been fixing up her parents' home with hopes of turning it into a vacation rental. Now she's not sure it's salvageable.

"When you get tired and get pooped, it's OK to stop," O'Brien said to Murter and Rogers, whose clothes, hands and faces were smeared with mud.

Video above: Couple describes moment home was swept into Yellowstone River

Yellowstone will partially reopen at 8 a.m. Wednesday, more than a week after more than 10,000 visitors were forced out of the park when the Yellowstone and other rivers went over their banks after being swelled by melting snow and several inches of rainfall.

But the northern half of the nation's oldest national park, which is marking its 150th anniversary this year, is expected to remain closed through the summer, if not longer, along with one of the major entrances to the park through Montana. The closure will deprive visitors from seeing Tower Fall and Lamar Valley, one of the best places in the world to see wolves and grizzly bears.

Meanwhile, outside of the population centers that border the park, there's a maze of damaged roads. A key bridge that leads to the town of Fishtail collapsed, causing traffic to divert through a single-lane county road. There are about 500 people in Fishtail.

Lee Johnson and his wife and daughter run the restaurant Montasia, so named because it's a fusion of Malaysian and Montana cuisine. He said business has plummeted.

"When we opened for the first time after the flood, it started just dead. And you start to have that sense of dread creep in. Did I do all this, did I sink all this money in, have I started this business and people can't even get here anymore?" Johnson said.

Johnson and his Malaysian wife Yokie took over the lease on a landmark 124-year-old Fishtail building earlier this year, transferring their restaurant from another part of the state. For Yokie, the business was a dream come true.

Video above: Yellowstone flooding hits nearby Montana towns

"Not being from Montana, I wanted to own something," she said. Going into business with her family was her biggest goal. Yokie said running the restaurant gives her strength as she battles cancer.

"I'm not sure how much time I have left, so the time I have left I want to be with my family, work with them every day, see them every day," she said.

Johnson said he is humbled by the chance to support his wife and determined to keep the restaurant open while the flood damage is repaired.

"You hitch your wagon to this community and it's just a matter of keeping up," he said.

Wolves are pack animals, living in family groups led by a matriarch and her mate. Some wolves stay with their pack their whole lives, helping hunt and raise pups like aunts and uncles as they mature, but others split off to find a mate of their own and start their own packs.

Related video above: Woman spots pack of wolves in Yellowstone

There are lots of factors that go into these types of behavior, such as quirks of personality and family relationships established as pups, but new scientific findings revealed a surprising influence on wolf-pack dynamics: a mind-controlling parasite that makes a gray wolf engage in riskier behavior.

Researchers found that gray wolves in Yellowstone National Park infected with a parasite known as Toxoplasma gondii were more likely to leave the group of wolves they were born into or become a pack leader.

The startling revelations could change scientists' understanding of wolf-pack dynamics and improve conservation efforts for an apex predator that plays a major role in the health of its mountain ecosystem.

Biochemical crossfire

If you've ever owned a cat, chances are you've heard of toxoplasmosis, an infection caused by T. gondii, a single-celled parasite. Its life cycle is closely entwined with cats — due to unique enzyme activity, cat guts contain an excess of an acid that T. gondii needs in order to reproduce. The parasites reproduce in a cat's intestines, and then the cat sheds the parasite's oocysts (single cells that are sort of like eggs) in its feces.

When other mammals or birds eat or drink something contaminated by those hardy oocysts, they become infected as well. But other animals' guts don't have the linoleic acid content that T. gondii needs to reproduce, so the parasite has to find its way back to a member of the cat family.

The parasites enter the intermediate host's brain and muscle tissue and change its behavior in a way that boosts its chances of getting eaten by a cat. The mechanism isn't yet clear to researchers, but the phenomenon is most well known in rodents: Mice infected with T. gondii seem to lose their inherent fear of cats and no longer avoid the scent of cat urine, studies have shown. These daredevil mice make an easy meal for a cat, and in eating them, the newly infected feline unwittingly sets the process in motion once again.

When it comes to evolutionary survival, T. gondii is optimized for cats and their prey, but other animals can get caught in the biochemical crossfire, with similar behavior-altering results. Even humans can be affected. Some behavioral changes — including taking risks in business, road rage and even schizophrenia — may be associated with T. gondii infection. And now, a recent study in the journal Communications Biology has shown the first evidence of T. gondii's effect on gray wolves.

Risky behavior of infected animals

Scientists have been monitoring wolves in Yellowstone National Park since the species was reintroduced there in 1995. Pack behavior is observed via trail cameras and plane flyovers, and about a quarter of the wolves wear radio tracking collars and undergo blood tests. These tests revealed that some of the wolves are infected with T. gondii, likely the result of sharing habitat space with cougars.

The presence of T. gondii caught the eye of researchers, including the study's co-lead author Connor Meyer, a doctoral student at the University of Montana's Ungulate Ecology Lab. Since T. gondii tends to influence an animal's tendency to take risks, Meyer said he and his colleagues decided to zero in on wolves behaving boldly, asking themselves, "What behaviors can we measure and have we measured for 25 years? And then, what of those behaviors do we think can be considered risky?"

A wolf puts itself in danger when it leaves its family and goes off to join or form a new pack, so the researchers looked back on a quarter century's worth of records of wolf dispersal and pack leadership, linked with blood test results from all the wolves in the study.

The study team found something startling: "A wolf that is positive for toxo is 11 times more likely to disperse than a wolf that's negative," said wildlife biologist Kira Cassidy, a research associate at the Yellowstone Wolf Project and co-lead author of the study. "And then becoming a pack leader was even more of an impact: A wolf that was positive was 46 times more likely to become a pack leader than a wolf that was negative."

Related video above: A pack of wolves is called a wolfpack, so what are other animal groupings called?

Wolf-pack distribution and conservation

Given the behavioral patterns associated with T. gondii in other animals, the researchers suspect that toxo is responsible for these trends. "We assume that there might be some sort of link between boldness caused from toxo and being more willing to leave your home range and go to another wolf's territory and possibly be killed," Meyer said.

Christina Hansen Wheat, a behavioral ecologist at Stockholm University, said she's excited to see further explorations from the research team.

"One thing I would be really interested to ask would be, how does this parasite affect other behaviors?" said Hansen Wheat, who was not involved with the study. She noted that boldness might account for a wolf leaving its pack, but wondered if other behaviors, including aggression, might be present in its dealings with its packmates, maybe leading them to being "actively expelled."

Ultimately, wolves infected with toxoplasmosis may not lead T. gondii back to its preferred feline host, but the parasite could be playing an unexpectedly large role in the lives of wolf populations. Hansen Wheat said that understanding how wolves disperse and interact with each other, both on their own and under the influence of mind-controlling parasites, can help us better meet their needs.

"The more we learn about wolf behavior, the better we can understand how to conserve the species," she said.

A man who picked up a bison calf in Yellowstone National Park caused it to be shunned by its herd, prompting park officials to kill the animal rather than allow it to be a hazard to visitors.

Park officials quickly defended the decision to kill the newborn bison.

"We made the choice we did not because we are lazy, uncaring or inexpert in our understanding of bison biology. We made the choice we did because national parks preserve natural processes," the park said in a statement posted Tuesday on Twitter.

Related video above: Unidentified man could face charges after bison calf encounter, Yellowstone National Park officials say

Park officials' options for dealing with the animal were limited, according to the statement, which said bison must be quarantined before being sent to conservation herds outside the park. A bison calf abandoned and unable to care for itself is not a good candidate for quarantine, the statement said.

The calf became separated from its mother when the herd crossed the Lamar River in northeastern Yellowstone on Saturday. The unidentified man pushed the struggling calf up from the river and onto a roadway, park officials said in a news release.

Human interference with young wildlife can cause animals to shun their offspring. Park rangers tried repeatedly to reunite the calf with the herd but were unsuccessful.

At one point, visitors saw the calf walking up to and following cars and people. This created a hazard, so park staff killed the animal, according to the news release.

It's the latest example of Yellowstone visitors getting in trouble or hurt after approaching bison. Park officials euthanized a newborn bison after a similar incident in 2016, when a Canadian man and his son put the calf in their SUV, thinking they could rescue it.

The man pleaded guilty. He was fined $235 and ordered to pay $500 to the Yellowstone Park Foundation Wildlife Protection Fund.

Bison have gored several people in Yellowstone in recent years, often after they got too close to the animals.

Many of Yellowstone's larger animals — including bison, which can run up to 35 mph and weigh up to 2,000 pounds — are deceptively dangerous, even when they are just grazing or resting.

Video below: Bison herd blocks cars while strolling along a national park road in Wyoming

Park rules require visitors to keep at least 25 yards away from wildlife including bison, elk and deer, and at least 100 yards away from bears and wolves.

Park officials are investigating the bison calf incident. The suspect was a white male in his 40s or 50s who was wearing a blue shirt and black pants, the statement said.

The calf's body was left on the landscape, similar to the 25% or so of Yellowstone's newborn bison that don't survive, park officials said in the Twitter statement.

"Those deaths will benefit other animals by feeding everything from bears and wolves to birds and insects. Allowing this cycle of life to play out aligns most closely with the stewardship responsibility entrusted to us by the American people," the statement said.

A Montana reporter got an unexpected lesson in social distancing – from bison.

KTVM reporter Deion Broxton was getting ready for a live report from Yellowstone National Park when he noticed some bison approaching him and his vehicle.

“Oh my God, oh my God. Oh no, I’m not messing with you,” Broxton can be heard saying in a video. "Oh no. Oh no. Oh no, I'm not messing with you."

Here's the video of the bison I shot once I got a safe distance away lol

pic.twitter.com/uL3XiR2ISR

— Deion Broxton KTVM (@DeionNBCMT)

March 26, 2020

When the animals got too close for comfort, Broxton made the executive decision to bail and stashed his camera in his car.

Once at a safer distance, Broxton shot video of the bison and you can see why he was so intimidated. They were large.

The video of Broxton’s hilarious reaction has now become a meme, used when people are not happy with a situation.

When Yellowstone park officials caught wind of the video, they

praised the reporter

for offering “a perfect example of what to do when approached by wildlife!”

The National Park Service even

offered a handy graphic

to remind people to practice social distancing with wild animals.

“Social distancing means avoiding large gatherings and maintaining distance (6 ft) from others. While we're at it, remember to keep it at least 300 ft for larger wildlife,” NPS wrote.

Bison have been known to charge people, even when not provoked, but attacks by the animals aren’t exactly common. Yellowstone officials say they typically see one or two each year.

For now, Yellowstone is closed to visitors until further notice because of the coronavirus pandemic.