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This article by Bradley Worrell was first published on July 29, 2026, in Colorado Arts and Sciences Magazine.

Fifty years ago this week, a beautiful summer evening in Colorado ended in catastrophe.

On the night of July 31, 1976, a powerful thunderstorm stalled over the Big Thompson Canyon west of Loveland, unleashing a torrential rainfall in a matter of hours. The resulting flash flood killed 144 people and became the single deadliest disaster in the state’s history.

For Lori Peek, professor of sociology and director of the Natural Hazards Center at the University of Colorado Boulder, the flood’s most important legacy may be the lessons that emerged from it—and the realization that those lessons still require attention today.

“Anniversary events like this one are so important because they serve as moments for communities to come together and reflect upon what was lost, what we’ve learned, and what we still need to do to become more resilient in the future,” she said.

A perfect storm of human, environmental, and built factors

While the Big Thompson Flood is often remembered for its meteorological extremes, Peek said that disasters are never caused by nature alone.

“One of the things we say in this field of study is that there are natural hazards, but there’s no such thing as a natural disaster,” she said. “Every disaster has a human component.

“There are, of course, natural hazards—floods, fires and tornadoes—but what turns them into disasters is the collision between vulnerable built environments, vulnerable human systems, and the natural environment. That’s what creates a disaster.”

In the case of the historic Colorado flood, several factors converged to maximize the damage. These included:

• Storm stalled: Rather than moving through an area as storms tend to do, the storm that evening stalled over the canyon, dumping more than 12 inches of water in just over four hours. “It was almost like pouring water into a bowl,” Peek said.

• Rapid water rise: The floodwaters rose with astonishing speed, leaving many people trapped in cabins, automobiles or low-lying areas before they understood the danger.

• Geography: The canyon’s steep walls funneled water into a narrow corridor, placing people in homes, hotels, campgrounds and vehicles along the river in harm’s way. “The topography played a major role,” Peek acknowledged.

• Nightfall: The storm struck after dark, when many people were sleeping. Also, of those who were awake, some could not see or sense the danger.

• Cars: Many victims were in cars—either trying to flee the storm or parked near the river. “The people with the highest risk of dying were those who remained in their vehicles,” Peek said.

• Timing: The storm struck during the final holiday weekend of the summer, when the canyon was crowded with campers and visiting tourists, as well as a mix of full-time and part-time residents. In total, it is estimated that about 2,500 people were in the canyon at the time.

  “There’s also the human dimension—whether people understood the risk, knew what to do, could physically take action, and could get to safety,” Peek said. “That complicated mix is what led to so many deaths.”

Research conducted soon after the flood found that survival often depended upon a simple but critical decision: getting out and moving uphill.

“What the research on who survived and why—and who died and why—showed was that the key to survival was getting out … and literally climbing to safety,” Peek said. That finding is one of the flood’s most enduring lessons.

A (new) sign of the times in 1977

Today, anyone who travels through Colorado canyons is likely familiar with the bright yellow signs depicting a person climbing uphill. According to Peek, those signs endure because they communicate something essential: Survival depends upon taking immediate action.

“If you’re going to communicate risk effectively, the message has to be actionable,” she explained. “That’s why, even 50 years later, the signage remains so powerful. It tells people exactly what to do in the face of an imminent threat to life safety.”

Peek notes those climb-to-safety signs were the result of an August 1977 working paper by CU Boulder researcher Eve C. Gruntfest, who interviewed dozens of flood survivors, first responders, emergency management professionals and others to learn what worked and what needed to be improved following the Big Thompson Flood. Gruntfest studied under Gilbert F. White, founder of the Natural Hazards Center and a CU Boulder professor of geography who is widely considered the father of floodplain management.

The Natural Hazards Center was not established because of the Big Thompson Flood, as White was already in the process of founding the organization in 1975. However, Peek said the flood demonstrated why such an academic research center, dedicated to translating and sharing findings, was needed.

“The Natural Hazards Center was established because, at the time, a lot of research wasn’t making it into the hands of practitioners and policymakers,” said Peek, who was a graduate research assistant at the center from 1999 to 2005. She returned to CU Boulder in 2017 to serve as the Center’s director. “The Natural Hazards Center was established to nurture the hazards and disaster research community and share information with those concerned with reducing disaster risk. That’s the work that federal agencies like the National Science Foundation support us to do, because the evidence shows that actions we take before disaster can save lives and prevent unnecessary harm and suffering.”

Comparing the floods of 1976 and 2013

In many ways, Colorado today is better prepared for flooding than it was in 1976. At the time of the 1976 disaster, emergency managers lacked many of the tools that are the norm today. Then, there were no cellphone alerts, no modern emergency notification systems, no social media networks and few of the sophisticated weather forecasting capabilities available today.

Peek said that weather forecasting has become more precise, at-risk communities have installed warning sirens and emergency communication systems can distribute alerts through many channels and in many different languages to serve diverse groups.

In the Big Thompson Canyon, some vulnerable structures destroyed in the 1976 flood were never rebuilt in the same locations.

“Portions of the built environment have been moved out of the highest-risk floodways and floodplains,” Peek said. “Some of the streamside motels, cabins, and other structures that were destroyed in the flood were not rebuilt in those same vulnerable locations.”

When the Big Thompson River flooded again in 2013, Peek said it demonstrated both the value of those improvements and the continuing reality of flooding danger. While the 2013 flood caused massive damage and resulted in at least eight deaths, Peek believes losses would have been even worse without decades of investment in warning systems and flood mitigation.

Why some lessons go unlearned

Despite the progress made since 1976, recent disasters show that communities do not always implement best-practice safety measures. Peek points to the 2025 Camp Mystic tragedy in Texas, where children were swept away in a flash flood.

“They didn’t have an emergency action plan. They didn’t have sirens. They didn’t have timely cell phone alerts. They hadn’t moved structures in the floodplain out of harm’s way,” she said.

Why do these failures persist?

Peek offers several reasons. While disasters can create “policy windows” for lawmakers and regulators to act, those windows close more quickly today due to short public attention spans, and consensus is harder to build in today’s age of political polarization, she notes. Additionally, even when guidance exists, people may not know where to begin or may be overwhelmed, she adds.

Still, Peek sees some reasons for optimism. New guidance documents from the Association of State Floodplain Managers provide step-by-step instructions for camps and RV parks to create emergency action plans and offer model ordinance language for lawmakers.

“That’s a good example of how progress happens,” she said. “Such guidance can help spur action.”

A state that has changed—and largely forgotten the storm

Meanwhile, back in Colorado, one of the bigger challenges in commemorating the anniversary of the Big Thompson Flood is that most Colorado residents—and nearly all of its visitors—have no memory of it.

“Fifty years is a long time,” she notes. “Most visitors would have no reason to know anything about the Big Thompson Flood unless they are particularly interested in disaster history.”

Even among residents, Colorado today is a relatively young state demographically. Many people weren’t alive when the flood occurred, and many didn’t attend school here. As a result, public awareness of flood risk remains low.

“People are often surprised to learn that Boulder is one of the state’s communities most at risk to flash flooding,” Peek said.

At the same time, Colorado itself has changed dramatically since 1976. The state’s population has swelled from 2.6 million then to more than 6 million today. More people are hiking, camping, and driving through canyons than ever, oblivious to the dangers that flash floods pose. And while technology has improved, many of those areas are still without reliable cell service, Peek notes. She adds that floods can strike with little warning.

Could a disaster like the 1976 Big Thompson Flood could happen today?

Peek’s answer is an unequivocal yes. That’s why physical signage, emergency planning measures, public education, and land-use planning all remain essential—especially in a warming climate, she said.

“Risk isn’t static,” she said. “As we experience more extreme rainfall events, places that once weren’t considered high risk, or weren’t mapped as flood hazards, may now be vulnerable.”

It’s also why remembering anniversaries like the 1976 Big Thompson Flood still matters today.

“It’s so important to know our history,” she said. “The Big Thompson Flood remains the deadliest disaster in Colorado’s history. By learning what happened, how lives could have been saved then and how lives can still be saved today, we have an opportunity to build a more resilient state.”