The Sedimentary Record The Making of a Perfect Racetrack at the Bonneville Salt Flats Brenda B. Bowen1,2*, Jeremiah Bernau1, Evan L. Kipnis1, Jory Lerback1, Lily Wetterlin1, and Betsy Kleba3 1Geology and Geophysics, University of Utah, Salt Lake City, UT, USA 2Global Change and Sustainability Center, University of Utah, Salt Lake City, UT, USA 3Lab & Operations, Exact Sciences, Salt Lake City, UT, USA *[email protected], 115 S 1460 E, Salt Lake City, UT, 84112-0102, (801) 585-5326 THE STORY OF THE SALT human presence— a century of racing, mining, and It is a unique experience being out on the salt at the recreation; and now, additionally, mitigation and adaptation Bonneville Salt Flats. The sun seems a bit too bright as light of diverse stakeholder communities reacting to the ever- reflects off the cubic halite crystals that cover the stark saline changing conditions. ground (Figure 1). There is a sense of isolation and vastness The Bonneville Salt Flats (BSF) is a perennial salt pan with the curvature of the earth visible on the horizon. There that spans over ~75 km2 adjacent to the Utah–Nevada is a profound silence. The only sound on some hot, dry days border (Figure 2). The extension of the Basin and Range is the crackling of halite crystals as they precipitate from lays the tectonic framework for the development of shallow brines. Void of any macro flora or fauna, the salt flat interbasinal playas, like the Bonneville Salt Flats, where ecosystem is only apparent in thin layers of bright green or groundwater flowpaths focus discharge and concentrate pink halite below the surface, or the insects that are trapped solutes in springs rimming playa boundaries (Gardner in the growing salt. Wagon tracks left when the ill-fated and Heilweil, 2014). On glacial-interglacial time scales, Donner Party became bogged in the sediment in 1846 the impact of Pleistocene Lake Bonneville and a cold reportedly remained visible in the salt for over 90 years; a and wet climate regime are evidenced by a series of tufa- vivid reminder of the dangers of this harsh landscape. Car traced shorelines stepping down the southeast face of the tire tracks have long since replaced wagon tracks. Each year Silver Island Mountains, bounding the salt flats to the in the late summer, when the salt crust permits, the silence northwest, and by the vast lacustrine playa surface that of the salt explodes with the roars of racing motors. Land blankets the Great Salt Lake Desert. The Great Salt Lake speed records were set on the Bonneville Salt Flats through and BSF are both remnants of Pleistocene Lake Bonneville the 20th century; it is a landscape intricately linked with which drained at the end of the last glacial maximum and U.S. car culture. The final season of Mad Men shows the desiccated over the last ~13,000 years (Oviatt, 2015). As protagonist, Don Draper, speeding recklessly through the regional climate warmed and dried through the Holocene, night across the salt flats: a symbol of his fragile freedom the pluvial lakes of the Pleistocene glaciations disappeared, and the endless possibility of the West. The landscape has leaving both a sedimentary and hydrological footprint, called dreamers and innovators, daring them to push the as much of the groundwater in the Basin and Range limits of human speed. is dated to ~20 ka— Bonneville water (Gardner and The geology of the Bonneville Salt Flats tells a story of Heilweil, 2014). Isostatic rebound of the Bonneville lake landscape change on a range of temporal scales—from basin (Crittenden, 1963; Oviatt, 2015) and hypothesized tectonic processes over millennia to seasonal fluctuations to neotectonic faulting along the northwestern edge of the salt even shorter timescale events that change the surface with a flats moved the West Desert’s low point from further east to single storm event or week of sunshine. Humans have come the western edge of the basin at the modern BSF, where a to value this relict landscape, but the Bonneville Salt Flats wedge of salts concentrated and precipitated over thousands is an active and dynamic system, changing continuously of years. On human time scales, cycles of flooding, drying, in response to rain, wind, evaporation, and groundwater and automobile racing punctuate the seasonal transitions in flux. These are all factors over which humans have little the landscape. This combination of geologic and hydrologic direct control. The impacts of long term, natural, geological circumstances led to a thin (<2 m) accumulation of saline processes morph together with landscape responses to chemical sediments in the westernmost surface of the Great 4 | June 2018 The Sedimentary Record a moist surface that keeps tires cool. Through the mid-century, BSF had the long, straight, and uninterrupted distance racers need for both the “go” (acceleration) and the “woah” (slowing down). However, geology does not mandate that there always be a hard, stable halite surface that covers the >13 miles needed for high speed racing, and the racers have struggled in recent years to find stable salt over the continuous distances needed for setting high speed records. In 2014 and 2015 the international “Speed Week” and “World of Speed” events, historic and cultural landmarks for Bonneville racing, were cancelled Figure 1: The halite surface of the Bonneville Salt Flats in August of 2013 (photo credit: B.B. Bowen). due to unsuitable and unsafe racing conditions. In 2014 water covered the Salt Lake Desert— the Bonneville Salt century, topping 600 miles per hour surface year-round. The following year, Flats— the “fastest place on Earth.” and establishing a multi-generational the uppermost halite crust was thin Just north of Interstate-80 (I-80), racing community that is passionate and exposed the underlying clay-rich BSF is the home of the Bonneville about the salt and reliant upon a gypsum beds. It was slick as snot and Speedway, a landmark on the U.S. stable surface halite (NaCl) crust that unsuitable for racing. But in 2016 National Register of Historic Places must be several centimeters thick for and 2017, the halite crust was strong and an Area of Critical Environmental their sport (Figure 3). During most and racing enthusiasts brought record Concern, where ground speed late summers, the hard, seasonally numbers of speedsters to the West records have been set for over 100 repaved halite surface, level ground, Desert. In the summer of 2017, the years. The salt-paved landscape of consistent texture, moisture content, Bureau of Land Management reported BSF provides a rare resource for the and extensive area of BSF provide an over 30,000 visitors to the salt. The state of Utah and the international ideal playground for speed enthusiasts, “bad years” of 2014 and 2015 were motorsports community— an iconic bringing many different types and not the first time the racing has been frontier destination for land speed classes of vehicles to test their speed at cancelled. Racing cancellations during racing. Top ground speeds at BSF Bonneville (Noeth, 2002). The high the El Nino of 1982-1983 and again steadily increased through the 20th albedo and shallow water table provide in 1993-1994 due to flooding suggest Figure 2: A) MODIS satellite image (July 25, 2011) of the Bonneville basin and the West Desert of Utah with location of C shown by box; B) schematic map of area shown in A highlighting key features; C) False color (infrared to highlight water on surface in blue) Landsat satellite image from June 22, 2015 of the BSF playa located at 40o47’00” North, 113o50’00” West. Surface water commonly accumulates along a regional low bounding the northwest edge of the salt flat, adjacent to the Bonneville International Speedway. June 2018 | 5 The Sedimentary Record Figure 3: Historic photos of BSF: waterlogged in 1937 (left) and starting lineup in 1966 (right) (photos provided by Louise Noeth). that quasi-decadal cycles of seasonal million tons of NaCl and 128,000 addition of saline brine to the northern precipitation may lead to poor salt tons of KCl have been returned to the region has helped to maintain crust conditions and cancellations. surface of BSF as brine through the saturation levels in the shallow brine Perceptions of a diminishing salt Salt Laydown Project in an effort to aquifer. Ongoing research seeks to crust have resulted in long term slow or perhaps reverse depletion of test the specific impacts of both the efforts within the racing community the salt crust (White, 2004). Although extraction and mitigation efforts on to “Save the Salt” with discussions more solutes have been laid down the saline strata. about increased infrastructure and than extracted through mine-related Data-driven management of implementation of experimental solute processes over the last 20 years, the this valued landscape requires an transfers in an attempt to grow the mitigation efforts have not yielded understanding of the sedimentary surface salt crust. the intended results of growing the history of BSF and active South of I-80, the salt flats surface salt crust. It is possible that the sedimentological processes impacting morph into organized patterns of solar evaporation ponds (Figure 4). Groundwater brines from below BSF have provided a rich source of potash (KCl) and saline resources have been harvested from this system for more than 100 years (Nolan, 1928). The potash is sold as a nutrient additive for fertilizers that have played a major role in allowing the agricultural industry to double global food production over the last fifty years (Johnston, 2002). More than 100 miles of collection ditches that re-route groundwater to the evaporation ponds outline the perimeter of the salt crust system.