Preliminary Assessment of Volcanic and Hydrothermal Hazards in Yellowstone National Park and Vicinity

Abstract

increasing frequency and intensity, the ground vibrations called volcanic tremor, localized uplift of the surface, ground cracks, and anomalous gas emissions. Of all the possible hazards from a future volcanic eruption in the Yellowstone region, by far the least likely would be another explosive caldera-forming eruption of great volumes of rhyolitic ash. Abundant evidence indicates that hot magma continues to exist beneath Yellowstone, but it is uncertain how much of it remains liquid, how well the liquid is interconnected, and thus how much remains eruptible. Any eruption of sufficient volume to form a new caldera probably would occur only from within the present Yellowstone caldera, and the history of postcaldera rhyolitic eruptions strongly suggests that the subcaldera magma chamber is now a largely crystallized mush. The probability of another major caldera-forming Yellowstone eruption, in the absence of strong premonitory indications of major magmatic intrusion and degassing beneath a large area of the caldera, can be considered to be below the threshold of useful calculation.

238 U– 230 Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas

“…170 ka and ca. 75 ka (Christiansen et al, 2007). These rhyolites compose the Central Plateau Member (CPM) of the Plateau Rhyolite and cover much of the caldera floor (Christiansen and Blank, 1972;Christiansen, 2001).…”

“…Zircon saturation temperatures for the West Yellowstone flow rhyolite are~800°C based on the model of Boehnke et al (2013), with pyroxene-fayalite and Fe-Ti oxide phenocryst compositions yielding temperatures of 845-860°C (Vazquez et al, 2009). Only the youngest chevkinite model age overlaps the 114 ± 2 ka eruption age derived by 40 Ar/ 39 Ar dating of sanidine (Christiansen et al, 2007). Dating of near eruption growth on the chevkinite crystals is likely to require ion microprobe sampling of unpolished rim surfaces of individual crystals in the same manner that has been used for other accessory minerals (e.g., Schmitt et al, 2011;Vazquez and Lidzbarski, 2012).…”

“…40 Ar/ 39 Ar eruption age of ca. 115 ka(Christiansen et al, 2007) is denoted by vertical dashed line.…”

Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling

“…The Biscuit Basin flows have been subdivided into the north, south (255 ± 11 ka), middle (516 ± 7 ka), and east flows (Gansecki et al 1996;Bindeman and Valley 2001;Bindeman et al 2008;Girard and Stix 2009). The Scaup Lake flow is the youngest WUBM rhyolite, 257 ± 13 ka, and is located southeast of the Biscuit Basin Flows (Christiansen et al 2007). The older UBM rhyolites and Blue Creek flow (post -HRT) are the first known intracaldera rhyolites that followed caldera collapse and have up to 5% depletion in d 18 O values with slightly elevated radiogenic Sr and Pb signatures (Hildreth et al 1984;Bindeman and Valley 2001).…”

“…Post-LCT rhyolites are grouped into the Plateau Rhyolite as defined by Christiansen and Blank (1972). 40 Ar measurements of extra-caldera basalts and rhyolites have yielded ages from 590 to 80 ka (Bennett 2002;Nastanski 2002;Christiansen et al 2007). Ages of the younger intracaldera Central Plateau Member of the Plateau Rhyolite were measured using 238 U-230 Th and range between 166 and 70 ka (Vazquez and Reid 2002;Vazquez et al 2009) and 40 Ar/ 39 Ar ages estimates between 159 and o 60 ka (Dallegge 2008;Simon et al 2008).…”