2015 Best Paper Award – CSS

2015 Best Paper Award – Colorado Scientific Society

Jon White received the Colorado Scientific Society’s best paper of the year award for 2015. The award was presented at the CSS Annual Meeting on December 17th for his abstract and January 15, 2015 presentation of “The May 2014 West Salt Creek Landslide in Mesa County, Colorado”. Much of the presentation was derived from work that was included in the CGS Bulletin 55 – The West Salt Creek Landslide: A Catastrophic Rockslide and Rock/Debris Avalanche in Mesa County by Jon and co-authors Matt Morgan and Karen Berry, which was published later in September 2015.

Jon White (on right) receives award from Pete Modreski

Jon White (on right) receives award from Pete Modreski.

Abstract

On May 25th near the town of Collbran a very large rockslide rapidly moved almost 3 miles down the West Salt Creek valley, ultimately covering almost a square mile of the valley. The site is within the Plateau Creek basin below the northern flank of Grand Mesa, about 38 miles east of Grand Junction. Earlier the morning of the 25th, smaller precursor landslides occurred that blocked the flow of irrigation water. Tragically, while investigating the initial slide, three local men were killed when the main failure occurred at 5:45 pm. Their remains have not been recovered from landslide deposits that are up to 125 feet deep at the valley floor. Properly described as a sturzstrom rock avalanche, disaggregated shale and marlstone rock from the Green River Formation was pulverized and “flowed” in discrete avalanche surges. The most rapid avalanche pulse overtopped a 250-foot high ridgeline at an outside bend on the west side of the West Salt Creek valley. Preliminary estimates of maximum landslide velocity at that location, based empirically on the overtopped height, may be up to 75 miles per hour. The avalanche moved 39-million cubic yards of rock and soil down 2,100 feet of elevation and caused a 3-minute seismic wave train and 2.8 magnitude earthquake. Currently, a 2,800 by 700 by 500-foot rotated block of highly disturbed and potentially unstable rock remains immediately downslope from the headscarp. The back-tilt of the block has formed a large depression below the headscarp that has filled to form a large sag pond. The spill-over elevation is 15 feet above the current level, at which point the total capacity of the lake will be about 410 acre-ft. In addition to the long-term instability of the block, this raises additional concerns with mud-debris flows with regard to potential pond breaches during next year’s spring runoff, as well as mini-tsunamis if retrogressive failures occur and large rock blocks fall from the headscarp to displace the water.


This presentation will discuss the timeline of the slide, the initial emergency response and on-going landslide study, the geology of the area (and evidence of geologically recent and historic landslide activity), UAV photogrammetry and LiDAR imagery, and a preliminary assessment of the deposit and slide mechanics, as well as the future long-term hazards in the area where this valley-constrained rock avalanche occurred.