Floods were considered a blessing by certain civilizations—the Egyptians relied on the Nile’s yearly overflow for fertile soil—but they also stand as some of history’s most devastating natural disasters. Whether due to heavy rains, storm surges or busted dams, deluges have often claimed thousands of lives and left whole cities in ruin. In some cases, they even permanently changed the planet’s geography.
1. The Johnstown Flood was so massive it equaled the flow of the Mississippi River.
The disaster began shortly after 3 p.m on May 31, 1889, when a dam on Pennsylvania’s Lake Conemaugh washed away following several days of drenching rain. The collapse unleashed some 16 million tons of water, which quickly turned into a 40-foot-high, half-mile-wide surge of mud and debris. An hour later, the wave struck Johnstown like a giant fist, crushing some 1,600 buildings and sweeping away everything in its path. When the waters finally receded, over 2,200 people were dead and many more were injured or homeless. The flood was later blamed on the poorly maintained dam, which was owned by a hunting and fishing club, but no one was ever held financially liable for the disaster.
2. The Central China Flood may have killed as many as 3.7 million people.
In the summer of 1931, heavy snowmelt, torrential rains and seven different cyclonic storms combined to produce the most devastating flood in Chinese history. In the month of July alone, central China was swamped by as much precipitation as it typically received in a year-and-a-half. By August, the Yangtze, Yellow and Huai Rivers had all burst through their badly managed dikes and flooded an area larger than the size of England. Thousands died from drowning during the initial phase of the flood, but even more followed due to widespread famine and outbreaks of diseases such as cholera, typhoid fever and dysentery.
3. One flood was known as the “Great Drowning of Men.”
The Grote Mandrenke was the result of a vicious North Sea tempest that swept across parts of Europe in January 1362. The effects of the storm were first felt in England, where one chronicler wrote that “a strong gale blew from the north so violently for a day and night that it flattened trees, mills, houses and a great many church towers.” The damage was even worse in the Netherlands, Germany and Denmark, which experienced a catastrophic storm surge that overran nearly every dike and levee in its path. Anywhere from 25,000 to 100,000 people drowned, and it was said that 60 different parishes in Denmark were “swallowed by the salt sea.” Elsewhere in the Low Countries, erosion from the flood permanently transformed the coastline and led to the disappearance of whole islands. Along with other storms during the Middle Ages, the Grote Mandrenke also played a role in forming a shallow North Sea bay in the Netherlands known as the Zuiderzee.
4. Few floods in recorded history compare to the one that rocked the Indus River Valley in 1841.
The trouble began in January of that year, when an earthquake triggered a massive landslide on the slopes Nanga Parbat, a Himalayan peak located in what is now Pakistan. So much bedrock tumbled off the mountain that it blocked the flow of the rushing Indus River and created a lake 500 feet deep and several dozen miles long. When the natural dam finally burst that June, the lake emptied at a rate of 540,000 cubic meters per second, unleashing a gargantuan flood wave almost 100 feet high. The casualties from the disaster were not recorded, but it was known to have wreaked havoc on several hundred miles of the Indus Valley. Whole villages were wiped off the map, and an entire 500-man Sikh army was reportedly consumed near the city of Attock.
5. The United States’ most iconic river was the source of its most destructive freshwater flood.
In the spring of 1927, following months of unrelenting rain, the lower Mississippi River swelled to its breaking point and overran its levee system. The resulting flood swamped some 16 million acres across seven states from Cairo, Illinois, to New Orleans. The damage was at its worst in Arkansas, Mississippi and Louisiana, where the river inundated so much land it temporarily created a shallow sea over 75 miles wide and forced thousands to be evacuated by boat. By the time the waters finally receded later that summer, at least 250 people were dead and another 1 million had been driven from their homes—roughly one percent of the entire American population at the time.
6. This 1966 flood struck a devastating blow to Italy’s cultural treasures.
The deluge began on November 4, when a period of steady rain caused the Arno River to overflow, sending 18 billion gallons of mud and sludge pouring through the streets of Florence. Thousands of homes and businesses were destroyed, but the water also reached several art galleries and libraries containing priceless Renaissance-era relics. Some 1.5 million books were left submerged in the Biblioteca Nazionale. Elsewhere in the city, the torrent destroyed or damaged 1,500 frescoes, sculptures and paintings. In the wake of the disaster, a band of international volunteers known as the “Mud Angels” descended on Florence to pick through the debris and salvage waterlogged canvases and manuscripts. The teams rescued countless artworks, but in many cases, the restoration process has taken decades. Work on one famous painting, Giorgio Vasari’s 1546 “Last Supper,” was only completed in 2016.
7. Not all of history’s great floods can be blamed on Mother Nature.
During the Second Sino-Japanese War in June 1938, Chinese Nationalist troops intentionally destroyed several dikes on the Yellow River in an attempt to thwart invading Japanese forces. The Chinese hoped the scorched earth tactic would block Japanese access to a railway and slow their westward progress. What happened instead was an environmental disaster. Once the muddy river was set loose, it tumbled off course and flooded a 21,000-square-mile swath of Henan, Anhui and Jiangsu provinces in the center of the country. An estimated 4 million people were displaced from their homes, and 800,000 died from drowning, disease and famine after the deluge continued unchecked. “Residents who have not died in the floods perish from hardship,” read a 1940 Chinese government report. “Those who have fortunately stayed alive are already urgently gasping for breath and groaning in agony.” The disaster dragged on for the rest of the war—the Chinese government initially tried to blame the busted dikes on a Japanese bombing—and it wasn’t until 1947 that engineers and laborers succeeded in returning the Yellow River to its original course.
8. Historians are still not entirely sure what caused one of Britain’s worst natural disasters.
The deluge began on the morning of January 30, 1607, when a great surge of seawater overran some 200 square miles of southwest England and Wales, completely drowning at least 20 villages. One witness wrote of seeing “huge and mighty hills of water, tumbling one over another” and advancing with “great swiftness” over the landscape. Such descriptions have led some researchers to theorize that the floods were the result of a massive tsunami brought on by an earthquake, but others maintain that a squall-induced storm surge and spring tide are the more likely culprits. Whatever its cause, the flooding proved devastating for the low-lying regions surrounding the Bristol Channel, where some 2,000 people were killed. In Somerset, the floodwaters surged 15 miles inland and briefly turned the famed hill at Glastonbury Tor into an island.