43 years ago this month, the biggest earthquake in Idaho’s history shook the Gem State.
Around 8 a.m. on October 28th, 1983, an earthquake that originated beneath Idaho’s tallest mountain rocked the towns of Challis and Mackay in central Idaho.
The magnitude 6.9 earthquake became known as the Borah Peak Earthquake.
“The quake originated along the Lost River Fault below Idaho’s tallest mountain, Borah Peak, at a depth of nearly 10 miles. The fault thrust the Lost River Mountains upward while dropping the Thousand Springs Valley lower,” Idaho’s Office of Emergency Management notes on its website. “Overall, the mountains and valley shifted apart nearly 14 feet in some places.”
The quake resulted in the death of two children.
“In the towns of Challis and Mackay, the brick and block masonry of the towns’ buildings crashed to the ground. Two schoolchildren, ages 6 and 7, were buried as a storefront collapsed,” Idaho’s Office of Emergency Management notes. “People who saw the blocks come down rushed to uncover the children but were unable to save them. They were the only deaths attributed to the quake.”
Borah Peak Earthquake also caused the most destruction, with over $12 million dollars in property damage.
“The most severe property damage occurred in the towns of Challis and Mackay, where 11 commercial buildings and 39 private houses sustained major damage and 200 houses sustained minor to moderate damage,” the U.S. Geological Survey’s website notes.
The earthquake also changed the flow of groundwater, left large cracks in the ground, and triggered rockslides and landslides in the area.
“Spectacular surface faulting was associated with this earthquake – a 35-kilometer-long northwest-trending zone of fresh scarps and ground breakage on the southwest slope of the Lost River Range with vertical displacement up to 2.7 meters observed between Mackay and Challis,” the USGS website notes. “The most extensive breakage occurred along the 8-kilometer zone between West Spring and Cedar Creek. Here, the ground surface was shattered into randomly tilted blocks several meters in width.”
More than four decades later, the permanent changes the earthquake made to Idaho’s landscape are still visible today.
For example, the 20-mile-long fault scarp can still be seen along the base of the Lost River Range in central Idaho.
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