HEART MOUNTAIN/MCCULLOUGH PEAKS STURZSTROM (~2.08 MA, HMMPS), THE WORLD’S LARGEST LANDSLIDE

Geomorphological studies document that allochthonous Paleozoic rocks on Heart Mountain and McCullough Peaks (north and northeast of Cody, WY, respectively) and on some outlying areas owe their origin to massive, seismically induced and earthquake propagated landsliding during an episode of cataclysmic silicic volcanism that accompanied both the deposition of the Huckleberry Ridge Tuff during collapse of the Island Park Caldera in the Yellowstone area and the emplacement of the Enos Creek/Owl Creek Debris-avalanche 90 km to the south during the early Pleistocene. Internal composition of the landslide breccias indicates dynamic disintegration and granular flow during emplacement by which immense blocks up to 17,150 m³ were rafted atop finer debris up to 60 km from their source in allochthonous masses of Paleozoic carbonate rocks in the Natural Corral area that were emplaced in the early Eocene (~49.5 MA) by detachment faulting. HMMPS debris descended nearly 900 m from source, then swashed up about 400 m to cover the McCullough Peaks Pediment. The long, nearly 70 km run-out of the debris, the thinness of the most distal debris, and a horizontal displacement of >70X the vertical displacement defines the feature as the largest known sturzstrom in the world. (Warner, A.J., and Bown, T.M., eds. 2024. The Heart Mountain Detachment Fault: A Critical Reappraisal. Bloomington, IN; Archway Publications:1-124.)