With no warning a 2,250 feet long and 150 feet wide crack formed in the foothills of the Bighorn Mountains in Wyoming. This crack in the earth was not formed by an earthquake and there was no seismic activity associated with the crack, leaving many wondering what formed this massive break in the earth’s surface in less than 2 weeks.
The 100 feet deep crack is in an area where there is no seismic activity, no oil and gas drilling, or commercial development, it left many wondering what had caused this crack and whether it was likely to reoccur nearby. The crack is located on state-owned land surrounded by private ranches used to herd cattle. The crack poses no danger to people or property based on its location in a remote area of Wyoming surrounded by state and private land.After inspection from local geologists, it was concluded that the crack had formed as a result of a wet spring saturating the topsoil in the area. This saturated topsoil became unstable and with the aid of small springs on either side, the whole block slid out. Average annual rainfall in Ten Sleep, Wyoming, nearby the crack is 13.11 inches.Often time’s underground springs will find pathways of least resistance. This could have caused a change in orientation of the springs to align with an inactive legacy fault or a weaker sedimentary unit. This deformation is a result of slope failure by gravity alone, although it was undoubtedly hastened by saturated soil conditions.
This form of slope failure is called a slump, where a coherent unit of sediment moves a short distance down a slope due to gravitational forces. The common causes of slump are soil wetting/drying, and freeze and thaw cycles. Slumps will have shear planes which are slightly concave upward and outward. A slump is different from other mass transport deposits such as turbidites, debris flows, or landslides in that the sediment remains relatively in tact and moves as one cohesive unit a short (less than a mile typically) downslope.
“Wyoming is a geologic wonderland, and this is just an example of that wonderland,” said Wyoming state geologist Tom Drean