Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics (original) (raw)
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Eruptions at Lone Star geyser, Yellowstone National Park, USA: 2. Constraints on subsurface dynamics
Journal Of Geophysical Research: Solid Earth, 2014
We use seismic, tilt, lidar, thermal, and gravity data from 32 consecutive eruption cycles of Lone Star geyser in Yellowstone National Park to identify key subsurface processes throughout the geyser's eruption cycle. Previously, we described measurements and analyses associated with the geyser's erupting jet dynamics. Here we show that seismicity is dominated by hydrothermal tremor (~5-40 Hz) attributed to the nucleation and/or collapse of vapor bubbles. Water discharge during eruption preplay triggers high-amplitude tremor pulses from a back azimuth aligned with the geyser cone, but during the rest of the eruption cycle it is shifted to the east-northeast. Moreover,~4 min period ground surface displacements recur every 26 ± 8 min and are uncorrelated with the eruption cycle. Based on these observations, we conclude that (1) the dynamical behavior of the geyser is controlled by the thermo-mechanical coupling between the geyser conduit and a laterally offset reservoir periodically filled with a highly compressible two-phase mixture, (2) liquid and steam slugs periodically ascend into the shallow crust near the geyser system inducing detectable deformation, (3) eruptions occur when the pressure decrease associated with overflow from geyser conduit during preplay triggers an unstable feedback between vapor generation (cavitation) and mass discharge, and (4) flow choking at a constriction in the conduit arrests the runaway process and increases the saturated vapor pressure in the reservoir by a factor of~10 during eruptions.
Special Paper of the Geological Society of America
Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam-and liquid-saturated fl uids with temperatures at or near the boiling curve underlie thermal fi elds. Sudden reduction in confi ning pressure causes fl uids to fl ash to steam, resulting in signifi cant expansion, rock fragmentation, and debris ejection.
Geological Society of America Special Papers, 2009
Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam-and liquid-saturated fl uids with temperatures at or near the boiling curve underlie thermal fi elds. Sudden reduction in confi ning pressure causes fl uids to fl ash to steam, resulting in signifi cant expansion, rock fragmentation, and debris ejection.
Open-File Report
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.
2004
Following the 2002 M 7.9 Denali fault earthquake, clear changes in geyser activity and a series of local earthquake swarms were observed in the Yellowstone National Park area, despite the large distance of 3100 km from the epicenter. Several geysers altered their eruption frequency within hours after the arrival of large-amplitude surface waves from the Denali fault earthquake. In addition, earthquake swarms occurred close to major geyser basins. These swarms were unusual compared to past seismicity in that they occurred simultaneously at different geyser basins. We interpret these observations as being induced by dynamic stresses associated with the arrival of large-amplitude surface waves. We suggest that in a hydrothermal system dynamic stresses can locally alter permeability by unclogging existing fractures, thereby changing geyser activity. Furthermore, we suggest that earthquakes were triggered by the redistribution of hydrothermal fluids and locally increased pore pressures. Although changes in geyser activity and earthquake triggering have been documented elsewhere, here we present evidence for changes in a hydrothermal system induced by a large-magnitude event at a great distance, and evidence for the important role hydrothermal systems play in remotely triggering seismicity.
Eruption mechanisms and short duration of large rhyolitic lava flows of Yellowstone
Earth and Planetary Science Letters, 2017
Large-volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers. We integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from Yellowstone. These large-volume (10-70 km 3) crystal-poor rhyolite lavas erupted within the Yellowstone caldera as 100-200 m thick flows and have a cumulative erupted volume of 650 km 3 that is similar to less frequent caldera-forming events, but occur as individual eruptions spread over ~100 ka. Most of this work is focused on the axisymmetric 124 ka, ~50 km 3 Summit Lake flow. We examined crystallinity, major and trace element concentrations, oxygen and hydrogen isotopic values, and quartz morphology and zoning in samples from the center to margin of this flow. Water contents down to 0.1 wt.% and D values of-110‰ are low and require closed-system degassing until near-surface lithostatic pressure, while major elements are consistent with water-undersaturated pre-eruptive storage and crystallization at ~4-8 km depth. We found some evidence for subtle km-scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high-Ti cores and ~200 μm thick rims on quartz phenocrysts. Embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of a magma bodies during shallow transport between dikes and sills. Modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at ~800˚C occurred over ~2 to 5 years with high discharge rates >100 m 3 /s. Such high magma discharge rates are accommodated through ~6 km-long fissures that allow for slower magma ascent velocities of <1 cm/s required for eruptions to remain dominantly effusive. Lower temperatures will result in >10 year flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed. Higher temperatures require unrealistically wide (>50 m) dike widths to accommodate large discharge rates. Petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow, ephemeral magma chamber. Large-volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures. Less-common explosive eruptions at Yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high. The results of this study provide a unique-top-down‖ constraint on effusive eruption rates, make new interpretations of common petrographic textures, and presents a comprehensive model for eruption control.
About the Mechanism of Geyser Eruption
arXiv: Geophysics, 2012
Essentially new physical mechanism of geyser eruption based on instability in "water-vapor" system is proposed. Necessary and sufficient conditions of eruptions are received. For group of Kamchatka geysers a good accordance of theoretical model with empirical observations is shown.
Heat flow measurements in Yellowstone Lake and the thermal structure of the Yellowstone Caldera
Journal of Geophysical Research, 1977
Twenty-two marine-type heat flow determinations in Yellowstone Lake indicate a rapid transition from high heat flow values outside the Yellowstone caldera, 100-300 mW m -2 (2.5-7.5 #cal cm -2 s-i), to an extensive area of very high heat flow, 600-700 mW m -a (14.5 •tcal cm -a s -l) and greater, within the caldera. The thermal transition occurs 5-10 km inside the mapped caldera boundary and approximately coincides with the point at which a zone of earthquake activity beginning outside the caldera terminates. Higher heat flow in West Thumb and Mary Bay (about 1600 mW m TM (40 #cal cm -• •-•)) outlines two thermal subprovinces within the calder a. The conductive heat loss beneath the lake is Similar in ma. gnitude to the average convective heat loss calculated from chloride budgets. Extr•tpolated temperatures beneatli the lake reach the boiling point under pressure at approximately 500-m depth, and d6eper temperatures probably increase along the boiling point curve in a laterally extensive geothermal reservoir to depths of the order of 800 + 400 m. Thermal areas in the park probably result from structurally and topographically controlled convection systems in this surficial system. A deeper, 'hotter fluid circulation system in fractures in the solidified granite postulated to underly the caldera at shallow depths (about I km) may exist at depth. The high heat flow is derived from a shallow cooling batholith beneath the caldera. J[NTRODUCTION Thermal events in the form of volcanic episodes have been the major agent in creating the spectacular geology of Yellowstone National Park. The park is famous for a remarkable array of geysers, hot springs, and other thermal phenomena, which in total number, variety, and activity are unsurpassed throughout the world. Situated in the northwest corner of Wyoming, overlapping the Montana and Idaho boundaries on the north and west (Figure 1), •he park lies on the eastern boundary of the broad region of high heat flow in the western United States which includes the Basin and Range, Columbia Plateau, and Rocky Mountain provinces [Roy et al., 1972], This broad region is an extensive tectonic zone characterized by Cenozoic volcanism and seismic activity [smith and $bar, 1974]. At the preseht time the boundaries of this zone appear to be the most active areas of vulcanicity and seismicity. Late Cenozoic and Quaternary volcanism of the Snake River Plain to the west-southwesi of Yellowstone indicates a progressive thermal history. Silicic volcanism started in Western Idaho synchronously with the eruption of the Columbia River basalt around 14-18 m.y.B.P. The onset of silicic vol-Canism progressed east-northeast toward Yellowstone at a rate of about 35 mm/yr, reaching the west margin of the park at approximately 1.9 m.y.B.P. [Armstrong et al., 1975]. The oldest cycle of volcanic activity in the Yellowstone area was in the Island Park caldera, centered just outside the park to the west-southwest. A second volcanic cycle was confined to the Island Park caldera and occurred around 1.2 m.y.B.P. The east-northeast progression of volcanism continued, with activity commencing in the Yellowstone caldera shortly after that event. Around 600,000 years ago a catastrophic eruption of rhyolite, pumice, and ash totaling more than 900 km 8 resulted in collapse along ring fracture zones to form the Yellowstone caldera [Boy& 1961; Eaton et al., 1975], 70 km long and 45 km wide, with its long axis trending east'noi'theast (Figure 1). Rhyolite flows as young as 70,000 years [Eaton et al., 1975; R. L. Christiansen, personal communication, 1974] have been extrudi:d: from vents in the fracture system and form a large rhyolite plateau in the west center of the park. There are no historical records of volcanic eruptions in Yellowstone National Park, but because of the long history of intermittent volcanism in the caldera area there is no reason to believe that the activity has ceased. Geophysical studies have provided evidence for the existence of a magma chamber beneath the caldera [Smith et at., 1974; Eaton et al., 1975]. The data'include the following: a large Bouguer gravity low (maximum closure of >50 mGal) over the rhyolite platea.u, with a steep gradient approximately following the mapped caldera boundary; a marked decrease in seismic activity within the caldera boundary associated with an abrupt change in maximum hypocentral depth from •20 km outside the caldera to 5•'krn i•n'side; and attehuation and local delay of P phase and shadowing of S phase seismic waves crossing the caldera. These results are consistent with the existence of a shallow magma chamber or magma plexis beneath the caldera. Heat flow is therefore an important parameter.neceSsary to the understanding of the structure and evolution of the Yellowstone caldera. The extensive 19ss of heat b• convection from the hydrothermal areas [Fournier et al., 1976], the extensive history of silicic volcanism [Christiansen and Blank, 1972, 1975a], and the high convective heat flow estimates [White, 1969] require on energy balance alone the presence of a large volume of still partially molten or recently solidified silicic rock. Hydrothermal activity in the park is structurally controlled by the caldera. Heat flow data from boreh0ies in the thermal areas have been interpreted •as indicating hydrothermal convection controlled by fracture systems [White et al., 1975]. In spite of extensive geochemical studies of the thermal regime of the whole park, however, with drilling and Paper number ½B0324. 3719 3720 MORGAN ET AL.: YELLOWSTONE SYMPOSIUM 111ø00' 110ø00'
Journal of Geophysical Research: Solid Earth, 2016
Steam-driven eruptions, both phreatic and hydrothermal, expel exclusively fragments of nonjuvenile rocks disintegrated by the expansion of water as liquid or gas phase. As their violence is related to the magnitude of the decompression work that can be performed by fluid expansion, these eruptions may occur with variable degrees of explosivity. In this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam-driven explosive energy. A series of fine-grained heterogeneous tuffs from the Campi Flegrei caldera were investigated for their petrophysical properties. The rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs. Our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy. Overall, the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple (Argon) gas expansion and may produce a higher amount of fine material even under partially saturated conditions. The energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles. Moreover, weak and low permeability rocks yield a maximum fine fraction. Using experiments to unravel the energetics of steam-driven eruptions has yielded estimates for several parameters controlling their explosivity. These findings should be considered for both modeling and evaluation of the hazards associated with steam-driven eruptions. The conversion of thermal energy stored in water into mechanical energy powers these eruptions. This conversion results in the fragmentation of the preexisting rocks, and acceleration and lifting of the resulting MONTANARO ET AL.