Here’s what you’ll learn when you read this story:

• A 10,000-ton ship tore apart Australia’s Tasman Bridge in 1975, severing the connection between the communities of Hobart and Clarence.
• The disaster claimed the lives of 12 people and fundamentally changed the two communities’ way of life.
• The bridge was not replaced for a full 34 months, causing the unique situation to turn into a harsh social experiment.

On the evening of January 5, 1975, a man named Frank Manley was driving his family home across the Tasman Bridge, in Hobart, Australia, in his new green HQ Monaro. The Manleys had spent the evening at a barbecue south of Hobart and were traveling back across the River Derwent toward the suburb where they lived. It was raining lightly and night was beginning to fall.

Below the Manleys, the 10,000-ton cargo vessel Lake Illawarra was nosing its way upriver, its hull loaded with zinc ore concentrate. Neither Frank Manley nor most of the ship’s crew had any reason to believe the next 60 seconds would change Tasmania forever.

But at 9:27 p.m., the Lake Illawarra drifted off course. Its wheelhouse struck two of the Tasman Bridge’s concrete pylons which caused a sound witnesses later described as a deep, sickening crack, like the Earth splitting open. Then came the impossible sight.

As Frank Manley crested the bridge in his car, the road lights died and the lane markings disappeared into nothing. “The bridge is gone!” his wife shouted. Frank braked hard. The Monaro skidded toward the gap, catching on the broken edge with its front wheels hanging over the 150-foot drop to the River Derwent below.

The family scrambled out quickly as the car pivoted. Frank Manley’s wife, his daughter Sharon, and his brother-in-law John exited the passenger side. Manley opened the driver’s door to near-empty space, hooking his arm over the roof to swing himself to safety. As he did so, his steel watchband left a scratch that’s still visible on the car today.

Nearby, another family’s EK Holden station wagon also teetered on the edge. Minutes after they evacuated it, another vehicle struck their car, pushing it closer to the void. Both cars sat there on the edge of the collapsed bridge span for hours with their headlights shining into the darkness, producing the disaster’s iconic photograph.

Sharon Manley ran up the bridge to warn traffic. A tourist bus bore down on her and the driver told her to move out the way, ignoring her warnings. Moments later, he saw the truth. Even police initially dismissed the emergency call as a prank.

Frank Manley and the family in the station wagon survived. But 12 others did not. When the Lake Illawarra struck the 3,000-foot structure, three full spans of roadway buckled and plunged downward. crushing the deck of the Lake Illawarra under a cascade of concrete. The ship sank immediately. Cars that had been traveling at highway speed vanished into the gap left by the fallen spans, their headlights swallowed by the river below. Five motorists drove into the void, and seven crewmen aboard the Lake Illawarra were buried beneath the rubble of the spans their ship had destroyed.

But the catastrophe that began that night would not end with the body count. For the roughly 100,000 residents who woke the next morning on opposite sides of the Derwent, the disaster was only beginning to unfold. What no one yet understood—not the government officials scrambling to respond, not the commuters staring in disbelief at the shattered crossing, not the families on the eastern shore suddenly cut off from hospitals, schools, and workplaces—was that the Tasman Bridge collapse was about to become a social experiment nobody asked for. The bridge would not be replaced for 34 months. And in that void, two communities with vastly different resources would be forced to reckon with what it means to be connected and what happens when that connection is violently severed.

“It was obvious to everyone that their own lives would be seriously disrupted,” the authors of a 1976-published report from the Australian Institute of Criminology, which examined the impact of the bridge collapse, “though at this stage the depth of disturbance was not really appreciated.”

The vastly different demographics of Hobart and Clarence were thrust into the limelight following the destruction of their connective bridge. They became shining examples of the inexplicable links present in contrasting ways of life.

Nothing was equal about the two sides of the river. Hobart, with its population of about 52,000, served as a true hub of activity, nestled on the western shore. It housed the region’s hospitals, schools, government offices, entertainment, businesses, and commerce. Clarence on the eastern side, on the other hand? It was home to roughly 40,000 people, the airport, and basically nothing more.

“The destruction of the bridge meant that the inhabitants of Clarence and the towns further afield were plunged into comparative isolation,” the 1976 report stated. “The situation was made worse since the eastern area was almost exclusively a dormitory suburb with a larger labor force that had to cross the water every day to its workplaces on the western shore.”

Almost anyone who had a job and lived in Clarence worked in Hobart. But with the three-minute trip via the four-lane bridge suddenly no longer on the table, the only commuting options available were a dangerous 1.5-hour drive down a dirt road or a woefully inadequate ferry. With intense ferry wait times, cross-river traffic was laborious, especially with so many workers needing to cross. For Clarence, unemployment rates jumped and alcohol consumption increased. Both led to an increase in crime—everything from minor offenses to violence.

The lessons were hard to learn for the residents of Clarence, but they did lead to significant systemic changes changes. “The Clarence municipality underwent a marked period of development with improved services, industry, and infrastructure,” archivist Bruce Kay wrote. “Other suburbs, such as Kingston, also accelerated their growth as an alternative suburb within an easy commute of Hobart.”

It was nearly a year before the Australian Army put the temporary one-lane Bailey bridge in place to re-open the river crossing, and just shy of three years before the government had its replacement bridge built (in October of 1977). Throughout the intervening period, official channels did what they could to support the community’s renewed effort towards improving infrastructure, and continued to do so once the new bridge (which had alternating pylons to help prevent another catastrophe) had been built. The hallmark of this effort was the opening of a second bridge, known as the Bowen Bridge, across the river in 1984.

The ferry industry experienced the longest-lasting impact. As ferry services continued to increase during the Tasman Bridge outage, local boat builder Bob Clifford modernized historic catamaran designs to pioneer a catamaran ferry now seen the world over.

The lessons of the Tasman Bridge disaster were deadly, violent, and tragic, but if a silver lining can be found, they did prompt lasting change for the inhabitants of Tasmania.