The Great Fire of 1910, also occasionally referred to as the "Big Burn," is believed to be the largest single fire in recorded U.S. history. It burned more than 3 million acres in Idaho, Montana and Washington — in all, a total area roughly the size of Connecticut. There were 87 fatalities from the fire and 78 of those were firefighters. The handling of the blaze went on to shape the future of the U.S. Forest Service. Immediately after the 1910 fire, the service vowed to fight all wildfires, even ones that are naturally occurring and of no threat to human life or property. The merits of this policy are still debated today, especially by ecologists who insist that some wildfires are necessary for ecosystem health.

Source: 10 of the worst wildfires in U.S. history. URL: http://www.mnn.com/earth-matters/wilderness-resources/stories/10-of-the-worst-wildfires-in-us-history

The "Tri-State Tornado," which killed 695 people and injured 2,027, was the deadliest tornado in U.S. history, according to the National Oceanic and Atmospheric Administration. The tornado traveled more than 300 miles through Missouri, Illinois and Indiana on March 18, 1925, and was rated an F5, the most powerful under old Fujita scale (winds of 260-plus mph).

Source: The 10 deadliest U.S. tornadoes on record. URL: http://www.cnn.com/2013/01/30/us/deadliest-tornadoes/

The Great Galveston Hurricane of 1900 was the deadliest hurricane to ever hit the United States and caused between 8,000 and 12,000 deaths. The storm reached the Texas coast south of Galveston on September 8 as a Category 4 hurricane with a storm surge of 8 to 15 feet. The lack of warning and the high storm surge caused this storm to have the highest death toll of any United States hurricane.

Source: What was the Largest Hurricane to Hit the United States? URL: http://geology.com/hurricanes/largest-hurricane/

This extratropical snowstorm impacted over 22 states throughout the Appalachians. The gusts peaked in Concord, New Hampshire at up to 160 miles per hour, and at the time, it was the costliest storm the US had ever seen, with $66.7 million worth of damages (not adjusting for inflation). Between the winds and the devastating cold front, the storm killed 353 people and injured 160 more.

Source: 10 worst winter storms the U.S. has ever seen because things have gotten way more. URL: http://www.bustle.com/articles/60600-10-worst-winter-storms-the-united-states-has-ever-seen-because-things-have-gotten-way-more/image/271638

This disaster saw two nuclear reactors meltdown. It was subsequently the worst disaster in commercial nuclear power plant history. Small amounts of radioactive gases and radioactive iodine were released into the environment. Luckily, epidemiology studies have not linked a single cancer with the accident. Chernobyl, Ukraine was a Level 7 disaster.

Source: A Nuclear Meltdown Survivor Story. URL: http://www.thedailybeast.com/articles/2011/03/17/three-mile-island-worker-on-how-he-survived-nuclear-catastrophe.html

With damage stretching from Pittsburgh to Cairo, Illinois, one million people were left homeless, with 385 dead and property losses reaching $500 million ($8 billion in 2012 dollars). Federal and state resources were strained to aid recovery, as the disaster occurred during the depths of the Great Depression and a few years after the Dust Bowl.

Source: The Ohio River Flood of 1937. URL: https://en.wikipedia.org/wiki/Ohio_River_flood_of_1937

The earthquake and resulting fires caused an estimated 3,000 deaths and $524 million in property loss. Damage in San Francisco resulting only from the earthquake was estimated at $20 million; outside the city, it was estimated at $4 million. The sensible duration of the shaking in San Francisco was about 1 minute. In areas where dislocation of fences and roads indicated the amount of ground movement, motions of 3 to 4.5 meters were common. The region of destructive intensity extended over a distance of 600 kilometers. The total felt area included most of California and parts of western Nevada and southern Oregon.

Source: Historic Earthquakes, USGS. URL: http://earthquake.usgs.gov/earthquakes/states/events/1906_04_18.php

Mt. Saint Helens is one of the several Cascade Range volcanoes. On May 18 an enormous column of ash thrust 15 miles into the sky. It continued to eject ash for about nine hours. The plume deposited ash and pumice downwind from the volcano. The ash was blown eastward by the wind at about 60 miles per hour. Some of the ash reached the eastern United States within 3 days. Small particles entered the jet stream and circled the Earth within two weeks. Superheated ash quickly melted and mixed with existing snow and ice, creating mud flows. Homes were carried away and deposited many miles downstream, or simply, destroyed by bridges.

Source: Mt Saint Helens Facts. URL: http://educatoral.com/msh_facts.html