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American author and historian David McCullough’s first book, The Johnstown Flood (1968), tells the story of a flood that devastated a steel community in Central Pennsylvania in 1889. He interviewed some of the few survivors to learn what happened during and after the disaster.

Johnstown is located around seventy miles east of Pittsburgh in a very deep valley. It was originally built at the intersection of two rivers, and it’s prone to flooding because heavy rainfall can cause severe problems. To help prevent this, the state constructed a dam on one of those rivers in 1853.

As the use of railroads increased, there was less need for canals and rivers. The government sold its canal system to private speculators who wanted to turn it into a lake for vacationers. They lowered the height of the dam so that cars could drive across it, making it weaker than before. They removed some pipes and relief valves from the dam as well as scrap metal, which made repairs difficult in case of heavy rainfalls or other emergencies. Finally, they filled in holes with mud and straw instead of fixing them properly.

During the late 1800s, a large amount of rain fell in two days. The Conemaugh River was so swollen that water began to overflow the top of the dam. A group of nearby residents led by Elias Unger attempted to save the dam with different techniques, such as piling mud on top and digging ditches on its side. However, they soon realized that debris caught up in fish traps had blocked relief valves from allowing water through them. Meanwhile, these men sent telegraphs to authorities below but were ignored because their warnings were dismissed as false alarms too many times before.

By mid-afternoon, Unger and his men gave up on their efforts to save the dam. They were certain that it would break soon, so they headed for higher ground in order to survive. About an hour later, the dam broke and unleashed 14.55 cubic meters of water from the reservoir as if it was a raging river. The town of Johnstown was flooded with this much water which carried debris, trees and pieces of damaged houses along its path at ever increasing speed because of pressure built up over time by being blocked by a bridge under construction.

When the flood hit Johnstown, it had already killed hundreds of people in a number of small towns. The wave was sixty feet high and traveling at forty miles an hour when it reached Johnstown. A second surge came from the other direction after gravity pulled water back down the other side of the valley. In all, 2,209 were said to have died, though one survivor emerged later on in reports years later. Death toll quibbles aside, this event resulted in the largest loss of life outside military conflicts for United States history by far and surpassed only by two hurricanes and September 11 attacks on New York City.

After the disaster, many survivors sought legal damages. However, the courts ruled that it was an “Act of God,” which meant that they couldn’t find anyone liable for the damage. Other states in America have since adopted new precedents for dealing with liability concerning similar disasters and allow survivors to sue negligent and non-negligent parties.