Sara Peek

This report presents chemical and isotopic compositions of volcanic gases collected from thermal areas within Lassen Volcanic National Park in northern California from 1974 through 2019. As the southernmost volcano in the Cascade Range and designated a very-high-threat volcano by the U.S. Geological Survey, the Lassen Volcanic Center (LVC) requires consistent monitoring to assess potential volcanic hazards. In 2014, the California Volcano Observatory established a gas geochemical monitoring program at LVC to provide baseline data to evaluate future changes. Results demonstrate consistent spatial patterns in bulk gas chemistry that support a two-circulation-cell hydrothermal model previously established for LVC. Gas samples from circulation cell 1 thermal areas have higher helium isotope ratios (6.59–7.50 times the air value) than those from circulation cell 2 (5.86–6.52 times the air value), indicating a stronger magmatic signature. The Sulphur Works and Pilot Pinnacle thermal areas within circulation cell 1 consistently emit gases with the highest magmatic helium contents, suggesting gas at these areas best represents conditions in the underlying volcanic system. A slight decrease in helium isotope values since 1974 may indicate progressive dilution of magmatic helium-3 (3He) by radiogenic helium-4 (4He) in the absence of recent magma intrusion. Carbon isotope compositions of carbon dioxide across all thermal areas are relatively uniform (−9.7–−7.3 per mil), falling within the range observed at other Cascade Range volcanoes. Based on gas geochemical characteristics and site accessibility, the Sulphur Works and Pilot Pinnacle thermal areas represent optimal targets for continued monitoring of the LVC magmatic-hydrothermal system. This study includes the most comprehensive helium isotope dataset collected at LVC currently available and establishes critical baseline data for future volcanic monitoring efforts.

Less than a year after the 2018 Kīlauea caldera collapse and eruption, water appeared in newly deepened Halemaʻumaʻu crater. The lake—unprecedented in the written record—grew to a depth of ∼50 m before lava from the December 2020 eruption boiled it away. Surface water heightened concerns of potential phreatic or phreatomagmatic explosions but also offered a new means of possibly identifying eruption precursors. The U.S. Geological Survey Hawaiian Volcano Observatory (HVO) monitored the lake via direct visual observation, webcams, thermal imaging, colorimetry, and laser rangefinders. HVO also employed uncrewed aircraft systems to sample the water and measure near‐lake gas composition. The lake's δD and δ¹⁸O indicate a groundwater source with substantial evaporation. The initial sample had a salinity (total dissolved solids concentration) of 71,000 mg/L and was rich in sulfate (∼53,000 mg/L), iron (∼500 mg/L), and magnesium (∼10,000 mg/L). Subsequent samples were slightly more dilute. The water's pH (∼4), δ³⁴S (+4.3‰), and surface temperatures (up to 85°C) suggest, rather than significant scrubbing of magmatic volatiles, leaching of basalt and reactions with sulfate minerals resulted in high concentrations of sulfate and other solutes. Thermodynamic modeling and precipitate mineralogy indicate that water composition was controlled by iron oxidation and sulfate dissolution. Although the lake exhibited no detectable precursors before the next eruption, and phreatic or phreatomagmatic explosions did not materialize, our multi‐parameter approach to monitoring yielded an enhanced understanding of the hydrologic, geologic, and magmatic conditions that led to the formation of the unique and short‐lived lake.

First posted January 7, 2021 Contact HVO Hawaiian Volcano Observatory U.S. Geological Survey 1266 Kamehameha Avenue Suite A-8 Hilo, HI 96720 Kīlauea Volcano, on the Island of Hawaiʻi, is surrounded and permeated by active groundwater systems that interact dynamically with the volcanic system. A generalized conceptual model of Hawaiian hydrogeology includes high-level dike-impounded groundwater, very permeable perched and basal aquifers, and a transition (mixing) zone between freshwater and saltwater. Most high-level groundwater is associated with the low-permeability intrusive complexes that underlie volcanic rift zones and calderas and also act to compartmentalize the groundwater system. Hydrogeologic studies of Kīlauea in recent decades, accompanied by deep research drilling, have shown that high-level groundwater is more widespread than once understood, that permeability decreases dramatically at depth, particularly in rift zones, and that freshwater can occur at depths of as much as several kilometers below the local water table. Copious groundwater recharge causes near-surface conductive heat flow to be near zero over much of Kīlauea. Approximately 95 percent of groundwater discharge occurs offshore, accompanied by approximately 99 percent of the approximately 6,000 megawatts of heat supplied by magmatic intrusion. Here, we summarize current understanding of the groundwater system of Kīlauea Volcano and describe transient changes during the decade or more preceding the 2018 eruption sequence. The changes in groundwater chemistry and thermal structure beneath Kīlauea summit hold implications for volcanic-volatile transport and the potential for explosive volcanism. Between 2008 and 2018, the magma conduit beneath the lava lake likely created an adjacent zone of very hot rock that significantly delayed liquid groundwater inflow to the draining magma conduit. Sulfate concentrations in groundwater beneath Kīlauea summit, sampled at the National Science Foundation-funded drill hole 1.5 kilometers south-southwest of the lava lake, declined substantially between 2010 and present. This decline likely reflects, at least in part, the decreased effectiveness of volatile condensation and solution into groundwater (scrubbing). The vent opening in 2008 presumably focused volatile flux into the vicinity of the vent, and progressive drying of the surroundings further restricted interaction with the groundwater system. The decrease in sulfate concentrations in the drill hole between 2010 and 2018 likely reflects decreased effectiveness of scrubbing.

To characterize eruption activity of the iconic Old Faithful Geyser in Yellowstone National Park over past centuries, we obtained 41 new radiocarbon dates of mineralized wood preserved in the mound of silica that precipitated from erupted waters. Trees do not grow on active geyser mounds, implying that trees grew on the Old Faithful Geyser mound during a protracted period of eruption quiescence. Rooted stumps and root crowns located on higher parts of the mound are evidence that at the time of tree growth, the geyser mound closely resembled its current appearance. The range of calibrated radiocarbon dates (1233–1362 CE) is coincident with a series of severe multidecadal regional droughts toward the end of the Medieval Climate Anomaly, prior to the onset of the Little Ice Age. Climate models project increasingly severe droughts by mid‐21st century, suggesting that geyser eruptions could become less frequent or completely cease.

In the past two decades, the U.S. Geological Survey and the National Park Service have studied hydrothermal activity across the Yellowstone Plateau Volcanic Field (YPVF) to improve the understanding of the magmatic‐hydrothermal system and to provide a baseline for detecting future anomalous activity. In 2017 and 2018 we sampled water and gas over a large area in the southwest YPVF and used Landsat 8 thermal infrared data to estimate radiative heat flow. Most of the thermal activity in this region is in close proximity to the Yellowstone Caldera boundary. Springs and fumaroles discharge from a variety of lithologies, including some of the youngest rhyolites in the YPVF. Gas compositions and helium isotope ratios of most samples resemble those in other parts of the YPVF. The waters have meteoric origins, and tritium was detected in several samples. Thermal waters from some areas have compositions that plot along a line connecting thermal and nonthermal water endmember compositions. The thermal water endmember equilibrated at 160°C–170°C, lower than waters in Yellowstone's geyser basins. Heat discharged by springs and fumaroles originates from within the Yellowstone Caldera and is transported laterally by advection, mainly along the base of rhyolite flows that cover the inferred caldera boundaries.

El Ediacárico terminal inlcuye una serie de cambios drásticos en los ciclos biogeoquímicos, muchos de los cuales se asocian con modificaciones evolutivas en los registros fósiles correspondientes. Entre ellos destacan las condiciones redox, las cuales pueden haber causado un impacto profundo en la evolución animal temprana. Este trabajo destaca el significado de la lito-, bio- y quimioestratigrafía en la investigación geobiológica del tiempo profundo.