A dangerous storm system made its way through the American South on Thursday, causing damage and casualties across Alabama and Georgia.

So far, the tornadoes have resulted in at least nine deaths and 12 people with injuries severe enough to warrant a hospital visit, per The Associated Press.

Beginning Friday morning, emergency services scrambled to unearth people from the rubble. They estimate that there will be a better understanding of the severity of the damage later in the day.

Much of the damage incurred by the storm can be found in Selma, Alabama, a landmark of the civil rights movement, as well as Autauga County, Alabama and Spalding County, Georgia, per The New York Times.

Damage from the storm system could be found as far as Monroe County, Mississippi, where one home was flattened and others sustained considerable damage to their roofs.

The affected areas are working to recover in the aftermath of the storms and locate people both alive and dead.

Why was this storm system unusual?

This deadly storm system wasn’t brought on by one factor alone — it was a combination of a La Niña weather pattern, unusually warm temperatures in the Gulf of Mexico and the gradual eastward shift in tornado patterns, per AP.

A tornado requires two things to form: wetness and wind shear, which “describes how the wind changes speed and/or direction with height,” according to the National Weather Service. While wind shear is nearly always present, the amount of moisture in the air is unusual for this time of year.

According to The Associated Press, the Southeast is usually on the drier side this time of year, but the dew point was double the number it would normally be. These conditions created the so-called perfect storm.

Surface water temperatures were far above average, measuring in at 70 degrees, per AP. This allowed the air to soak up more moisture from the water than it would on average at this time of year.

“The warm humid air hits the cold front and goes up like a ramp and the mixing that creates tornadoes begin,” said Northern Illinois University meteorology professor Victor Gensini, according to AP.

Scientists have begun to study the eastward migration tornadoes have taken in the past few decades, but don’t have an answer as to why, as of yet.

According to AP, experts warn that the further east tornadoes happen, the more deadly they may become. Their reasoning comes down to population distribution.

In “tornado alley,” a tornado can run its course and not cause any damage or deaths because there isn’t anything in its path. The further east you get, the more buildings and people in close proximity to one another there are.

More vulnerable communities live in the southeast, namely those living in poverty and mobile home parks, which Harold Brooks, senior scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory, told AP is among the most dangerous places to be during a tornado.

Gensini worries that this is a strong indicator of a bad tornado year.