The Longfellow Boom is a loud and unexplained phenomenon reported in the Longfellow community of Minneapolis, Minnesota, United States. The booms reportedly generally take place on summer nights, and have been described by residents as "house-shakingly loud" and at lower tone, distinct from a car crash or gunshot. Those investigating the booms believe they are mostly likely caused by several types of unrelated human activities, such as fireworks and improvised explosives being lit in the Mississippi River gorge, trains decoupling, and cars backfiring.
While the phenomenon has been discussed for several decades, a number of explosions in South Minneapolis began to be reported to Minneapolis police in the mid-2000s. Many were attributed to fireworks; however, in 2010, the Third Precinct stated that while fireworks and exploding electrical transformers could account for half of the noises, the others were unexplainable. Originally discussing the phenomenon on internet chat forums, locals continue analyzing the topic on social media.
Many theories have been put forward attempting to explain the phenomenon but none have been confirmed. Other explanations include train cars coupling, secret NORAD flights, or improvised explosive devices. Another discredited theory, drawing FBI attention, was anarchists preparing for an attack on the 2008 Republican National Convention. Sewer issues or a fault line in the Mississippi River have also been posited, as well as extraterrestrial explanations. The neighborhood's proximity to the Mississippi River has also drawn out suggestions that the river causes otherwise-normal sounds to echo differently.
Xcel Energy has stated they have not found outages or equipment problems that correlate with the booms. A project based out of MinneapolisâÂÂSaint Paul International Airport using aircraft noise sensors was also unable to ascertain the origin of the booms. Likewise, the Minneapolis Police Department and Minneapolis Health Department, despite multiple investigations, have been unable to identify the cause.
Loud booms have also been reported in the neighboring cities of Saint Paul and Richfield. In 2024, Richfield police officers arrested a driver who they alleged was lighting off mortars from their car causing loud booms.
In 2026, some Longfellow residents reported the emergence of a mysterious hum sound, but it was determined to be caused by industrial fans atop the recently renovated Atkinson grain mill owned by ADM at East 38th Street and Hiawatha Avenue.
The Boom, a short film by Ajuawak Kapashesit released in 2026, is inspired by the mysterious phenomenon in the Longfellow area.