Mother Nature can be merciless. From the churning hurricanes of the Gulf Coast, to the trailer-tossing storms of Tornado Alley, to the ground-pounding quakes of California, the United States is no stranger to deadly natural disasters. Here are five of the worst natural disasters to wreak havoc on U.S. soil.

Galveston, Texas sits on a narrow barrier island in the Gulf of Mexico with a peak elevation of 8.7 feet above sea level. In 1900, Galveston was the gem of Texas, its biggest port city, home to millionaire mansions and some of the nation’s first electric streetlights.

All of that changed on September 8, when an unnamed hurricane bearing 140-m.p.h winds slammed into the Gulf Coast, generating a 16-foot storm surge that nearly wiped the island and its 37,000 residents off the map. An estimated 6,000 to 8,000 people perished in the storm, the single deadliest in U.S. history.

Among the harrowing details of the Galveston storm were trolley tracks ripped from their moorings and smashing through buildings like battering rams, a grand piano riding the crest of a six-foot wave down Broadway, and an unrelenting wind that survivors described as “a thousand little devils shrieking and whistling.”

But the greatest single tragedy belongs to St. Mary’s Orphans Asylum, where 93 children and 10 nuns took refuge in the girl’s dormitory after the boy’s was lifted off its foundation and washed away by the pounding waves. In desperation, each of the sisters bound herself with clothesline to eight to 10 children, and that’s how most of their bodies were found. Only three of the orphans survived the storm.

On April 18, 1906, the residents of San Francisco were awoken with a jolt at 5:12 am. They had just enough time to get their bearings before the real shaking began. For nearly a minute, the Northern California city of 450,000 was rocked with a 7.9-magnitude earthquake that ripped a 296-mile fissure along the San Andreas fault.

But the quake, which leveled countless buildings and homes, was only the beginning of the nightmare. Hundreds of fires burned across the city fueled by broken gas lines, and firefighters could only watch helplessly, their water supply drained by ruptured pipes. The fires raged for three days, consuming nearly 500 city blocks.

When the smoke finally cleared, city officials estimated that more than 3,000 people were killed in the earthquake and ensuing fires, more than 28,000 buildings were destroyed, and more than 200,000 San Franciscans were left homeless, forced to sleep in makeshift cottages in the city’s parks for months as the city was rebuilt from the ashes.

Tsunamis aren’t supposed to strike central Pennsylvania, but that’s exactly what it looked like when a 40-foot high, half-mile wide wall of water and debris roared down upon the Appalachian town of Johnstown in 1889. In minutes, 1,600 homes were flattened and washed away, and 2,209 people were dead, including 99 entire families.

The source of the Johnstown Flood was the failure of dam holding back 20 million tons of water contained in Lake Conemaugh, a manmade reservoir 14 miles from Johnstown in the mountains. The lake and dam were owned by South Fork Hunting and Fishing Club, which included wealthy industrialists Andrew Carnegie and Henry Clay Frick as members.

The club blocked off the dam’s drainage pipes to maintain the fish population and allowed the lake to fill up dangerously high with spring rains. When the dam collapsed on May 31, the massive rush of water tore down the mountainside, picking up trees and large boulders as the wave gained terrible speed and strength.

170,000-pound locomotives in the wave’s path were shoved 4,800 feet off their tracks. Houses were ripped from their foundations. And bodies were recovered as far away as Cincinnati, Ohio, more that 350 miles to the west.

The Great Chicago Fire is arguably the most famous fire in U.S. history, but a far deadlier if lesser-known blaze occurred on the very same day in neighboring Wisconsin and Michigan. The Peshtigo Fire, which consumed 1.5 million acres of tinder-dry land on October 8, 1871, was responsible for the deaths of an estimated 2,500 people, more than any other fire in American history.

Drought conditions in the upper Midwest triggered a string of wildfires, including the massive one that was believed to have originated near the small town of Peshtigo, Wisconsin. High winds fanned the flames into firestorms, tornado-like columns of fire that were able to leap natural firebreaks and even large bodies of water.

When the residents of Peshtigo heard the approaching inferno—it was reported to rumble like a freight train—many fled to the river, where they thought the flames couldn’t reach them. A local priest described the scene:

“The flames darted over the river as they did over land, the air was full of them, or rather the air itself was on fire. Our heads were in continual danger. It was only by throwing water constantly over them and our faces, and beating the river with our hands that we kept the flames at bay.”

Elsewhere, people weren’t so lucky. A group that took refuge in a water tower were boiled to death. Some fathers, unable to get their families to safety, chose to kill themselves and their children before the flames could reach them. The firestorm was so hot that it turned sand on the Peshtigo streets to glass.

America has a long and tragic history of murderous hurricanes. The carnage of the Great Galveston Storm of 1900 is unmatched, but there’s also the 1928 Okeechobee hurricane that claimed 2,500 lives in Florida and the 1893 Sea Islands storm that drowned 2,000 people in coastal Georgia and South Carolina.

But according to new data from Harvard public health researchers, Hurricane Maria, which ripped through Puerto Rico on September 20, 2017, may be one of the deadliest ever. The official death toll from the Category 4 storm is 64 people, but the scenes of devastation and stories from local hospitals hinted at a much larger toll.

By surveying 3,299 individual households across every inch of the island, researchers from Harvard’s T.H. Chan School of Health discovered that the death rate in Puerto Rico during the months immediately following Hurricane Maria was 62 percent higher than the same period a year earlier.

Those “excess deaths” totaled 4,645 people, making Maria the second deadliest hurricane in U.S. history, claiming more American lives that 9/11 and Hurricane Katrina combined.