Iowa, while not known for seismic activity, is not immune to earthquakes. Throughout its history, the state has seen significant earthquakes that have caused damage and agitated citizens. Let’s look at some of these major earthquakes and what they tell us about the geological landscape and potential threats in the region.
The 1867 Waverly Earthquake
The most severe earthquake in Iowa history, the 1867 Waverly earthquake, occurred on April 24, 1867, at about 9:30 a.m. The epicenter was in Waverly, Bremer County, in northeastern Iowa, and had an estimated magnitude of 5.5.
The quake’s impacts were felt throughout Iowa and surrounding states such as Minnesota, Wisconsin, Illinois, Missouri, and Nebraska. It cracked houses, chimneys, and windows, and tipped over furniture and dishes. Notably, it caused a 12-mile-long and 4-foot-wide fissure near the Cedar River, which was accompanied by rumbling sounds and flashes of light.
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This earthquake was likely caused by the reactivation of an ancient fault in the Precambrian basement rocks beneath Iowa’s sedimentary layers. The fault could have been pressured by glacier loading during the Ice Age or regional tectonic factors associated with Missouri’s New Madrid seismic zone. The occurrence highlighted Iowa’s seismic vulnerability, pointing to probable future earthquakes.
The 1909 Colfax Earthquake
The 1909 Colfax earthquake struck central Iowa around 5:40 a.m. on September 3, 1909. With a magnitude of 5.1, its epicenter was near Colfax in Jasper County. Its tremors spread across 200,000 square miles, hitting states like as Iowa, Minnesota, Wisconsin, Illinois, Missouri, Kansas, Nebraska, and South Dakota. It caused modest damage, such as plaster and masonry fractures and rattling windows and dishes, but it also generated landslides and sand boils along the Des Moines River.
This earthquake was most likely caused by fault movement in the Paleozoic sedimentary rocks that cover Iowa’s Precambrian basement. Influences could range from regional tectonic stresses to local factors such as groundwater extraction or coal mining. The occurrence exposed Iowa’s sensitivity to moderate earthquakes and raised the possibility of hidden faults underground.
The 1984 Perry Earthquake
The most recent widely felt earthquake in Iowa was on October 7, 1984, at 7:46 a.m., near Perry in Dallas County, with a magnitude of 4.5. Its tremors spread across about 400,000 square miles, hitting several states. Although it did not cause considerable damage, it did frighten several people and cause objects to swing or topple.
Seismometers throughout the country recorded the earthquake waves. Similar to the 1867 Waverly earthquake, the 1984 Perry earthquake was most likely caused by fault movement in the Precambrian basement rocks. Regional tectonic forces or local factors such as groundwater removal or oil and gas development could have caused the fault. This occurrence highlighted Iowa’s continued seismic activity and the possibility of greater earthquakes in the future.
Conclusion
In conclusion, while not generally linked with seismic events, Iowa has a history of significant earthquakes, including the 1867 Waverly earthquake, the 1909 Colfax earthquake, and the 1984 Perry earthquake. These incidents, caused by fault movements beneath Iowa’s geological layers, highlight the state’s seismic vulnerability and the need to understand and prepare for future earthquakes.