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Hydrothermal monitoring in a quiescent volcanic arc: Cascade Range, northwestern United States
Geofluids
Abstract
Ongoing (1996-present) volcanic unrest near South Sister, Oregon, is accompanied by a striking set of hydrothermal anomalies, including elevated temperatures, elevated major-ion concentrations, and 3He/4He ratios as large as 8.6 RA in slightly thermal springs. These observations prompted the U.S. Geological Survey to begin a systematic hydrothermal-monitoring effort encompassing 25 sites and 10 of the highest-risk volcanoes in the Cascade Range volcanic arc, from Mount Baker near the Canadian border to Lassen Peak in northern California. A concerted effort was made to develop hourly, multiyear records of temperature and (or) hydrothermal solute flux, suitable for retrospective comparison with other continuous geophysical monitoring data. Targets included summit-fumarole groups and springs/streams that show clear evidence of magmatic influence in the form of high 3He/4He ratios and (or) anomalous fluxes of magmatic CO2 or heat. As of 2009-2012 summit-fumarole temperatures in the Cascade Range were generally near or below the local pure-water boiling point; the maximum observed superheat was 0.001 J/m3 during periods of hourly record. Hydrothermal responses to these small seismic stimuli were generally undetectable or ambiguous. Evaluation of multiyear to multi-decadal trends indicates that whereas the hydrothermal system at Mount St. Helens is still fast-evolving in response to the 1980-present eruptive cycle, there is no clear evidence of ongoing long-term trends in hydrothermal activity at other Cascade Range volcanoes that have been active or restless during the past century (Baker, South Sister, and Lassen). Experience gained during the Cascade Range hydrothermal-monitoring experiment informs ongoing efforts to capture entire unrest cycles at more active but generally less accessible volcanoes such as those in the Aleutian arc. This article is protected by copyright. All rights reserved.
Supplementary resource (1)
Data
January 2014
... In porous fresh volcanic rocks, the resistivity of the rock is controlled by the resistivity of the saturating fluid (Archie, 1942). At Mount Baker, as at most other Cascade volcanoes, springs are dilute with low conductance (~100-1000 μS/cm (resistivity = 10-100 Ω-m)) (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b. During the increased fumerolic activity in 1975, the conductance of the lake that formed in Sherman Crater was nearly 4000 μS/ cm (resistivity = 2.5 Ω-m). ...
... By applying Archie's (1942) law for fully saturated rocks (bulk resistivity = fluid resistivity * porosity −cementation factor ) with a cementation constant of 2.45 typical for volcanic rocks (Revil et al., 2016), the range of porosities (b1-50%) for Cascades scoria and lava flows (Saar and Manga, 1999) and of water conductivity for Cascade springs (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b and the 1976 Sherman Crater lake (Bortleson et al., 1977), we illustrate the relations of bulk resistivities in our data and other samples with porosity and water conductivity ( Fig. 4b) relevant to inverted resistivity models described below. Clay rich samples are not plotted because they do not relate to this simple application of Archie's law. ...
... Low resistivity altered clay caps and their underlying saline rich hydrothermal systems (Afanasyev et al., 2018) have been imaged by deep sensing electromagnetic data within the edifices of a variety of volcanoes, sometimes connected to surface low-resistivity zones related to fumaroles; examples include Japan (Aizawa et al., 2008(Aizawa et al., , 2009(Aizawa et al., , 2005, Italy (Finizola et al., , 2006Revil et al., 2008Revil et al., , 2011, Peru Gonzales et al., 2014) and Indonesia (Müller et al., 2002). Baker Hot Springs, east of Mount Baker, and an unnamed tributary of Sulfur Creek south of Sherman Crater, both with elevated chloride contents (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b, could tap into this hydrothermal system, similar to flank hot springs at other volcanoes. ...
Water-saturated hydrothermal alteration reduces the strength of volcanic edifices, increasing the potential for catastrophic sector collapses that can lead to far traveled and destructive debris flows. Intense hydrothermal alteration significantly lowers the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks can be identified with helicopter electromagnetic and magnetic measurements. Geophysical models constrained by rock properties and geologic mapping show that intensely altered rock is restricted to two small (500 m diameter), >250 m thick regions around Sherman Crater and Dorr Fumarole Field at Mount Baker, Washington. This distribution of alteration contrasts with much thicker and widespread alteration encompassing the summits of Mounts Adams and Rainier prior to the 5600 year old Osceola collapse, which is most likely due to extreme erosion and the limited duration of summit magmatism at Mount Baker. In addition, the models suggest that the upper ~300 m of rock contains water which could help to lubricate potential debris flows. Slope stability modeling incorporating the geophysically modeled distribution of alteration and water indicates that the most likely and largest (~0.1 km³) collapses are from the east side of Sherman Crater. Alteration at Dorr Fumarole Field raises the collapse hazard there, but not significantly because of its lower slope angles. Geochemistry and analogs from other volcanoes suggest a model for the edifice hydrothermal system.
... (b) Peak ground velocity and inferred permeability change at Growler Hot Spring compared to PGVs observed to cause comparably large permeability changes at the Pinon Flat Observatory [Elkhoury et al., 2006]. In Figure 2a, hot spring and geyser responses are from Wang and Manga [2010], Sorey and Clark [1981], Silver and Vallette-Silver [1992], and Ingebritsen et al. [2014], who assessed the response of Cascade Range hydrothermal-monitoring sites to events that generated local seismic energy densities~≥0.001 J/m 3 (n = 87). ...
... Error associated with individual field measurements is 5-10%. Probe values are less accurate but reveal high-frequency variability associated with precipitation events; as observed elsewhere [Ingebritsen et al., 2014], high-frequency peaks may reflect flushing of hydrothermally sourced Cl À from local, near-surface storage. ...
... Chloride-flux measurements. Growler / Morgan Hot Springs is the most southerly of about 25 U.S. Geological Survey (USGS) hydrothermal-monitoring sites in the U.S portion of the Cascade Range [Ingebritsen et al., 2014]. Like many hot-spring complexes, the Growler / Morgan Hot Springs complex includes numerous vents: Morgan Hot Springs consists of about 25 springs and pools in a meadow along a ~0.5-km reach of Mill Creek, and there is also direct inflow of thermal water to the creek. ...
The increasing capability of seismic, geodetic, and hydrothermal observation networks allows recognition of volcanic unrest that could previously have gone undetected, creating an imperative to diagnose and interpret unrest episodes. A November 2014 earthquake swarm near Lassen Volcanic National Park, California, which included the largest earthquake in the area in more than 60 years, was accompanied by a rarely observed outburst of hydrothermal fluids. Although the earthquake swarm likely reflects upward migration of endogenous H2O-CO2 fluids in the source region, there is no evidence that such fluids emerged at the surface. Instead, shaking from the modest sized (moment magnitude 3.85) but proximal earthquake caused near-vent permeability increases that triggered increased outflow of hydrothermal fluids already present and equilibrated in a local hydrothermal aquifer. Long-term, multi-parametric monitoring at Lassen and other well-instrumented volcanoes enhances interpretation of unrest and can provide a basis for detailed physical modeling.
... In porous fresh volcanic rocks, the resistivity of the rock is controlled by the resis- tivity of the saturating fluid (Archie, 1942). At Mount Baker, as at most other Cascade volcanoes, springs are dilute with low conductance (~100-1000 μS/cm (resistivity = 10-100 Ω-m)) (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b. During the increased fumerolic activity in 1975, the con- ductance of the lake that formed in Sherman Crater was nearly 4000 μS/ cm (resistivity = 2.5 Ω-m). ...
... By applying Archie's (1942) law for fully saturated rocks (bulk resistivity = fluid resistivity * porosity −cementation factor ) with a cementa- tion constant of 2.45 typical for volcanic rocks (Revil et al., 2016), the range of porosities (b1-50%) for Cascades scoria and lava flows (Saar and Manga, 1999) and of water conductivity for Cascade springs (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b) and the 1976 Sherman Crater lake ( Bortleson et al., 1977), we illustrate the relations of bulk resistivities in our data and other samples with porosity and water conductivity ( Fig. 4b) relevant to inverted resistivity models described below. Clay rich samples are not plotted because they do not relate to this simple application of Archie's law. ...
... Low resistivity altered clay caps and their underlying saline rich hydrothermal systems ( Afanasyev et al., 2018) have been imaged by deep sensing electromagnetic data within the edifices of a variety of volcanoes, sometimes connected to surface low-resistivity zones re- lated to fumaroles; examples include Japan ( Aizawa et al., 2008Aizawa et al., , 2009Aizawa et al., , 2005), Italy ( Finizola et al., 2004Finizola et al., , 2006Revil et al., 2008Revil et al., , 2011), Peru ( Finizola et al., 2004;Gonzales et al., 2014) and Indonesia ( Müller et al., 2002). Baker Hot Springs, east of Mount Baker, and an unnamed tributary of Sulfur Creek south of Sherman Crater, both with elevated chloride contents (Ingebritsen et al., 2014a(Ingebritsen et al., , 2014b, could tap into this hydrothermal system, similar to flank hot springs at other volcanoes. ...
High‐resolution helicopter magnetic and electromagnetic (HEM) data flown over the rugged, ice‐covered Mt. Adams, Mt. Baker and Mt. Rainier volcanoes (Washington), reveal the distribution of alteration, water and ice thickness essential to evaluating volcanic landslide hazards. These data, combined with geological mapping and rock property measurements, indicate the presence of appreciable thicknesses (>500 m) of water‐saturated hydrothermally altered rock west of the modern summit of Mount Rainier in the Sunset Amphitheater region and in the central core of Mount Adams north of the summit. Alteration at Mount Baker is restricted to thinner (<300 m) zones beneath Sherman Crater and the Dorr Fumarole Fields. The EM data identified water‐saturated rocks from the surface to the detection limit (100–200 m) in discreet zones at Mt. Rainier and Mt Adams and over the entire summit region at Mt. Baker. The best estimates for ice thickness are obtained over relatively low resistivity (<800 ohm‐m) ground for the main ice cap on Mt. Adams and over most of the summit of Mt. Baker. The modeled distribution of alteration, pore fluids and partial ice volumes on the volcanoes helps identify likely sources for future alteration‐related debris flows, including the Sunset Amphitheater region at Mt. Rainier, steep cliffs at the western edge of the central altered zone at Mount Adams and eastern flanks of Mt. Baker.
... However, the record of hydrothermal measurement over the past several decades is quite rich. In fact, though one-time measurements have been done worldwide, much of the reliable data on time-variation of hydrothermal discharge derives from monitoring studies done by the USGS in the western United States from about 1980-present (e.g., Ingebritsen et al. 2001Ingebritsen et al. , 2014b. These data were collected for diverse purposes, including basic understanding of water-rock interaction, environmental-baseline monitoring, and volcano monitoring. ...
... More selective and frequent hydrothermal monitoring resumed at Lassen in 2009, using methods described by Ingebritsen et al. (2014aIngebritsen et al. ( , 2014bhttp://water.usgs.gov/nrp/cascade-hydrothermal-monitoring/). Ongoing (1996-present) volcanic unrest near South Sister, Oregon, has been accompanied by a striking set of hydrothermal anomalies (e.g., Evans et al. 2004), and the observations at South Sister prompted the USGS to begin a systematic hydrothermal-monitoring effort encompassing 25 sites and 10 of the highest-risk volcanoes (Ewert et al. 2005) in the Cascade Range, from the Canadian border to the Lassen volcanic center. ...
The active Lassen hydrothermal system includes a central vapor-dominated zone or zones beneath the Lassen highlands underlain
by ~240 °C high-chloride waters that discharge at lower elevations. It is the best-exposed and largest hydrothermal system
in the Cascade Range, discharging 41 ± 10 kg/s of steam (~115 MW) and 23 ± 2 kg/s of high-chloride waters (~27 MW). The Lassen
system accounts for a full 1/3 of the total high-temperature hydrothermal heat discharge in the U.S. Cascades (140/400 MW).
Hydrothermal heat discharge of ~140 MW can be supported by crystallization and cooling of silicic magma at a rate of ~2400
km3/Ma, and the ongoing rates of heat and magmatic CO2 discharge are broadly consistent with a petrologic model for basalt-driven magmatic evolution. The clustering of observed
seismicity at ~4–5 km depth may define zones of thermal cracking where the hydrothermal system mines heat from near-plastic
rock. If so, the combined areal extent of the primary heat-transfer zones is ~5 km2, the average conductive heat flux over that area is >25 W/m2, and the conductive-boundary length <50 m. Observational records of hydrothermal discharge are likely too short to document
long-term transients, whether they are intrinsic to the system or owe to various geologic events such as the eruption of Lassen
Peak at 27 ka, deglaciation beginning ~18 ka, the eruptions of Chaos Crags at 1.1 ka, or the minor 1914–1917 eruption at the
summit of Lassen Peak. However, there is a rich record of intermittent hydrothermal measurement over the past several decades
and more-frequent measurement 2009–present. These data reveal sensitivity to climate and weather conditions, seasonal variability
that owes to interaction with the shallow hydrologic system, and a transient 1.5- to twofold increase in high-chloride discharge
in response to an earthquake swarm in mid-November 2014.
... The volcanic system at Mount Rainier, classified a Decade Volcano by the International Association of Volcanology (Newhall, 1996), is a unique natural laboratory to assess the cycling of glacial melt at the summit crater and on the flanks of the volcanic edifice. Previous research at Rainier and the broader Cascade Volcanic arc (e.g., Frank, 1995;Ingebritsen et al., 2014;Zimbelman, 2000) has provided conceptual models to guide our fundamental understanding of the hydrogeology at Rainier. ...
The fumarole ice caves of Mount Rainier in the Cascade Volcanic Arc in Washington, USA, provide unique insight into the dynamic equilibrium between thermal flux of fumaroles on volcanic edifices and snow accumulation on summit glaciers. More than 3.5 km of surveyed cave passage nearly circumnavigate the East Crater, reaching within 19 m of the 4,392 m summit and extending to 144 m depth along the glacier‐crater boundary. The large circum‐crater passage connects entrances on the crater rim to steep transverse passages, and cave morphology is maintained by fumarole gas convection and advection. A melt‐ and condensate‐formed lake, Lake Adélie, occupies a portion of the circum‐crater passage. Hourly data were collected between August 2016 and August 2017 and included the measured temperatures at three fumaroles, the cave air temperature and pressure, the lake water temperature and depth, and the outside temperature and snow depth at Paradise Visitors Center. Time‐series analyses of these data reveal complex associations between synoptic to seasonal weather, fumarole activity, and lake level. On seasonal and longer scales, fumarole temperatures follow independent pathways connected to spatial and temporal changes in volcanic heat flux and the circulation of glacial melt. Major snowfall seals the cave entrances, increasing cave air temperature and pressure from fumarole output and causing rising lake levels from increased melt until entrances reopen. Repeating freeze‐thaw cycles observed in the cave monitoring data are a primary cause of crater mass wasting. Despite these transient variations, the scale and morphology of the caves is preserved over decadal or longer scales.
... A large number of 3 He/ 4 He measurements have been published for groundwater and gas samples collected from wells, springs, and geothermal systems in the NBR and modern Cascades arc (Welhan et al., 1988;Poreda and Craig, 1989;Evans et al., 2004;Saar et al., 2005;Kennedy and van Soest, 2007;Ingebritsen et al., 2014;Siler and Kennedy, 2016). These ratios are generally 0.1-1.0 ...
The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected ³He/⁴He ratios (with atmospheric He removed) range widely from 0.05 to 35.8 times the air ³He/⁴He ratio (RA), with a median of 1.43 RA. Forty-one percent of measured ³He/⁴He ratios are ≥4 RA, corresponding to ≥50% mantle He assuming a mantle ratio of 8 RA. These results suggest that mafic magmas were part of the magmatic-hydrothermal system underlying Goldfield and Tonopah, and that associated mantle-sourced volatiles may have played a role in ore formation. The three highest corrected ³He/⁴He ratios of 17.0, 23.7, and 35.8 RA indicate a primitive mantle He source and are the highest yet reported for any epithermal-porphyry system and for the Cascades arc region. Compiled ³He/⁴He measurements from epithermal-porphyry systems in subduction-related magmatic arcs around the world (n = 209) display a statistically significant correlation between ³He/⁴He and Au-Ag grade. The correlation suggests that conditions which promote higher fluid inclusion ³He/⁴He ratios (abundance of mantle volatiles and focused upward volatile transport) have some relation to conditions that promote higher Au-Ag grades (focused flow of metal-bearing fluids and efficient chemical traps). Results of this and previous investigations of He isotopes in epithermal-porphyry systems are consistent with the hypothesis posed in recent studies that mafic magmas serve an important function in the formation of these deposits.
... While the sampler suites were deployed, other variables that were continuously monitored (temperature, pressure, and electrical conductivity) exhibited no unusual variations (Ingebritsen et al. 2014). At Manzanita Creek, the R/Ra value for the smallest sampler agrees with the initial deployment conditions within 2 %. ...
Helium (He) concentration and 3He/4He anomalies in soil gas and spring water are potentially powerful tools for investigating hydrothermal circulation associated with volcanism and could perhaps serve as part of a hazards warning system. However, in operational practice, He and other gases are often sampled only after volcanic unrest is detected by other means. A new passive diffusion sampler suite, intended to be collected after the onset of unrest, has been developed and tested as a relatively low-cost method of determining He-isotope composition pre- and post-unrest. The samplers, each with a distinct equilibration time, passively record He concentration and isotope ratio in springs and soil gas. Once collected and analyzed, the He concentrations in the samplers are used to deconvolve the time history of the He concentration and the 3He/4He ratio at the collection site. The current suite consisting of three samplers is sufficient to deconvolve both the magnitude and the timing of a step change in in situ concentration if the suite is collected within 100 h of the change. The effects of temperature and prolonged deployment on the suite’s capability of recording He anomalies have also been evaluated. The suite has captured a significant 3He/4He soil gas anomaly at Horseshoe Lake near Mammoth Lakes, California. The passive diffusion sampler suite appears to be an accurate and affordable alternative for determining He anomalies associated with volcanic unrest.
... Pre-and syn-eruptive hydrogeochemical changes have been observed at several volcanoes (Hirabayashi et al., 1982;Takahashi et al., 1988;De la Cruz-Reyna et al., 1989;Martini et al., 1991;Gíslason et al., 1992;Shevenell and Goff, 1995;Tilling and Jones, 1996;Fischer et al., 1997;Quattrocchi et al., 2000;Varekamp et al., 2001;Federico et al., 2004;Armienta et al., 2008;Capasso et al., 2014). Nowadays, hydrogeochemical monitoring represents an important tool (Marrero et al., 2005;Rouwet et al., 2009;Capasso et al., 2014;Ingebritsen et al., 2014), that jointly with other seismic, geodetic and gravimetric monitoring data supply valuable information to reduce the degree of non-uniqueness of the interpretations. Such information furnishes a more accurate evaluation of the more likely volcanic activity scenarios, making it possible to issue adequate and on-time warnings of changes in a volcano condition. ...
El Chichón volcano has an eruptive record of at least 12 major eruptions in the Holocene, the latest one in March-April 1982 causing the worst volcanic disaster in the history of Mexico. After about 6 centuries of quiescence, this eruption destroyed a large dome and opened a 1 km wide crater. A lake, formed within the crater shortly after the eruption, has been an important source of information about the evolution of the post-eruptive processes. The fluctuations of the crater lake water physicochemical parameters, observed since 1983, have allowed identifying hydrothermal waters and H2S-rich gases, influenced by tectonic and meteorological effects, as the main contributors to its composition. Here we propose some methods to help assessing the state of the volcano derived from the relative contribution of these factors as an easy to implement volcanic surveillance method in potentially active volcanoes with crater lakes, or other volcano-influenced water sources.
... Pre-and syn-eruptive hydrogeochemical changes have been observed at several volcanoes ( Hirabayashi et al., 1982;Takahashi et al., 1988;De la Cruz-Reyna et al., 1989;Martini et al., 1991;Gíslason et al., 1992;Shevenell and Goff, 1995;Tilling and Jones, 1996;Fischer et al., 1997;Quattrocchi et al., 2000;Varekamp et al., 2001;Federico et al., 2004;Armienta et al., 2008;Capasso et al., 2014). Nowadays, hydrogeo- chemical monitoring represents an important tool ( Marrero et al., 2005;Rouwet et al., 2009;Capasso et al., 2014;Ingebritsen et al., 2014), that jointly with other seismic, geodetic and gravimetric monitoring data supply valuable information to reduce the degree of non-uniqueness of the interpretations. Such information furnishes a more accurate eval- uation of the more likely volcanic activity scenarios, making it possible to issue adequate and on-time warnings of changes in a volcano condition. ...
In 1982, a series of eruptions resulted in the worst disaster linked
with volcanic activity in México. The characteristics of the
phenomena together with a lack of prevention measures resulted in
approximately 2000 deaths. An important aspect to prevent disasters is a
thorough knowledge and monitoring of the potentially destructive natural
phenomena. Monitoring the activity of dormant or active volcanoes by
various methods is thus a key measure to estimate the hazard and design
adequate risk reduction measures. Despite of the 1982 volcanic disaster,
until only a few years, hydrogeochemical monitoring was the only regular
surveillance of El Chichón post-eruptive activity. The first
samples of the crater-lake water were collected by Casadevall et al. in
1983. Since 1985, a systematic sampling and chemical analyses program
has been carried out by the Geophysics Institute in collaboration with
local authorities from the State of Chiapas. Chemical analyses of main
ions and Rare Earth elements (REE) are performed in the Laboratorio de
Química Analítica and Laboratorio ICP-MS of the Instituto
de Geofísica, UNAM. Results are interpreted considering the
physico-chemical changes that may be recognized as precursors of
volcanic activity. The problem is difficult because at least two main
water reservoirs feed the crater lake; besides, dissolution of acid
volcanic gases, water-rock interactions and geochemical processes among
dissolved species have resulted in a complex chemical behavior of the
lake-water along the years. The calculated degree of neutralization, pH
values, and chloride and sulfate concentrations of samples taken at
different dates result in a classification of the volcano as active or
inactive according to the method developed by Varekamp. A pH of 0.5,
very high conductivity and a temperature of about 50°C characterized
the first years following the eruptions. An overall decrease on the
temperature and ionic concentrations, along with a less acid pH (around
2.5) have been measured during the last 20 years. However, important
changes on the individual concentrations of the main ions have also been
observed within this time. These changes show the dynamics of the lake
and the relative influence of the water sources, volcanic gases and
geochemical processes on the water samples. On the other hand, the lack
of REE elements concentration variations reflects some volcanic
stability in the period 2006 to 2008. These observations have led to the
identification of specific precursory hydrogeochemical parameters, that
contribute to the dynamic hazard assessment of El Chichón.
Temporal changes in volcanic water chemistry are reliable indicators of changes in volcanic activity. Conventionally, volcanic water discharges are monitored through repetitive sampling and subsequent laboratory analysis. Samples are usually taken at intervals ranging between weekly and annually due to the campaign-style of observations. However, samples collected in this way to track chemical changes were insufficient in terms of number, frequency, and temporal coverage/completeness to allow quantitative tracking of volcanic activity. In this study, we thus developed a field auto-sampling tool for collecting volcanic waters discharged near craters to improve the frequency of water sampling. The basis of the developed tool is a commercially available XY plotter, a drawing robot, which can be controlled by a computer numerical control (CNC) operator code called G-code. To collect the water in the arranged sampling bottles, the drawing pen of the XY plotter was replaced with a plastic drip pipe connected to a peristaltic pump. A field test using the G-code-Operated Field Auto-sampling Tool (GOFAT) was conducted at a hot spring at a crater area of Hakone volcano in Japan. Samples were collected at three-hour intervals for 40 consecutive days. The GOFAT successfully operated without stopping and collected a total of 332 water samples. Using the high temporal resolution samples obtained by the GOFAT, we observed short-term significant positive SO4 peaks that endured for approximately a day, which had not been detected by a repetitive sampling carried out in previous studies at this volcano. Our results clearly show the importance of high temporal resolution sampling, even during quiescent periods, to clarify the characteristics of the observed hot spring.
Continuous geochemical monitoring of thermal waters at Tokachidake volcano has been conducted for more than three decades to detect changes in its volcanic activity. Based on the geochemical data from 1986 to 2013, the origin and temporal changes of the thermal waters were discussed in our previous study. Here, we supplement the previous dataset with the geochemical data from 2014 to 2018 and comprehensively discuss the results of geochemical and geophysical monitoring to reveal the interactions between deep magmatic fluids, volcanic gases, and shallow aquifers. Thermal waters, discharging in the Tokachidake spa area, are formed by the interaction of volcanic gas and a shallow aquifer, and show the Cl change which have a significant correlation with the change in the volcanic plume height. This suggests a parallel volcanic gas input from the magma to the shallow aquifer and fumarole. Both changes are caused by a variation in the volcanic gas release rate from the magma. Around the 1988–1989 magmatic eruption, thermal waters in the Fukiage spa area showed remarkable thermal and chemical changes due to the interaction with the magmatic fluid (NaCl-type thermal water). Based on the chemical and isotopic compositions of the thermal waters, we calculated the Cl concentration and temperature of the NaCl-type thermal water as being approximately 20,000 mg/L and ∼280 °C, respectively. Our calculation of the supply rate of the NaCl-type thermal water indicates that large amounts of the NaCl-type thermal water are in continuous supply when volcanic activity increases prior to a magmatic eruption. In this area, the recent monitoring results reveal that the changes in the Cl concentration and seismic activity show a relatively good correlation, indicating that at least some of the volcanic earthquakes are related to the migration of the NaCl-type thermal water. Thus, when volcanic activity increases before a future magmatic eruption, chemical changes in the thermal waters in the Fukiage spa area should be apparent and the changes are likely to occur together with seismic activity. Our results propose that it is possible to interpret the present state of an active volcano more precisely through a comprehensive discussion of geochemical data from the thermal waters along with the other observations.
This paper reviews the hydrothermal systems of Kusatsu-Shirane volcano, Japan, which are associated with phreatic eruptions. The existence of hydrothermal systems at this volcano is easily explained: hot springs are derived from unique thermal water that results from condensation of magmatic gas. Kusatsu-Shirane also exhibits fumaroles characterized by high H2S and CO2 contents, which are separate from the condensation of magmatic gas. Clay layers composed of smectites control the subsurface flow of thermal water. Hypocenter distributions of microearthquakes approach from depth to a bell-shaped impermeable clay layer underlying the Shirane pyroclastic cone, indicating the clay layer’s role in storing thermal water supplied from depth. Sources of low-frequency earthquakes, ground deformation, and demagnetization/magnetization are located around the bell-shaped impermeable clay. These observations indicate that a hydrothermal reservoir exists under the clay layer. Phreatic eruptions seem to result from the growth of cracks connecting the reservoir to the surface. Precursory changes in volcanic activity precede phreatic eruptions at Kusatsu-Shirane in most cases; however, the contents of such precursors do not correlate with the ejecta mass, locations, and lead times of eruptions. Kusatsu-Shirane has been continuously monitored since the 1970s. The phreatic eruption of 1976 was predicted based on geochemical observations, but no precursor warning was detected before the onset of a series of phreatic eruptions in 1982-1983. Microearthquake swarms that occurred in 1989-91 and 2014 were followed by demagnetization and changes in the chemical composition of the water in Yugama Crater Lake and the fumaroles. These changes were similar to precursors of past phreatic eruptions at Kusatsu-Shirane, but no phreatic eruption occurred at Yugama Crater within 2-3 years of either set of changes. Multiparameteric monitoring, including geophysical and geochemical observations, is a powerful tool for detecting changes in volcanic activity, but it is difficult to identify precursors of phreatic eruptions.
From 2009 to 2015 the U.S. Geological Survey (USGS) systematically monitored hydrothermal behavior at selected Cascade Range volcanoes in order to define baseline hydrothermal and geochemical conditions. Gas and water data were collected regularly at 25 sites on 10 of the highest-risk volcanoes in the Cascade Range. These sites include near-summit fumarole groups and springs/streams that show clear evidence of magmatic influence (high ³He/⁴He ratios and/or large fluxes of magmatic CO2 or heat). Site records consist mainly of hourly temperature and hydrothermal-flux data. Having established baseline conditions during a multiyear quiescent period, the USGS reduced monitoring frequency from 2015 to present. The archived monitoring data are housed at (doi:10.5066/F72N5088). These data (1) are suitable for retrospective comparison with other continuous geophysical monitoring data and (2) will provide context during future episodes of volcanic unrest, such that unrest-related variations at these thoroughly characterized sites will be more clearly recognizable. Relatively high-frequency year-round data are essential to achieve these objectives, because many of the time series reveal significant diurnal, seasonal, and inter-annual variability that would tend to mask unrest signals in the absence of baseline data. Here we characterize normal variability for each site, suggest strategies to detect future volcanic unrest, and explore deviations from background associated with recent unrest.
Newberry Volcano in Oregon, USA, has two small crater lakes inside its caldera: East Lake and Paulina Lake. The 50-80 m deep lakes differ in morphology, water chemistry and sediment composition, although separated only by a narrow volcanic ridge. East Lake is a terminal lake with gaseous geothermal inputs, whereas Paulina Lake has an outlet (Paulina Creek) and subaqueous, high-alkalinity hot springs. The sediment in both lakes is organic-rich and mainly consists of diatom frustules (SiO2) with some volcanic ash, accumulating at sedimentation rates of 1.5-2 mm a⁻¹ (²¹⁰Pb dated). In Paulina Lake the sediment has up to 14% Fe2O3 of hydrothermal origin and 250 ppm As. Sediment in East Lake is Fe-poor but has up to 4 ppm Hg, and fish are also Hg-rich. Both lakes host productive ecosystems, with primary producers using geothermal CO2, P and Si, and nitrogen fixed by cyanobacteria (Nostoc sp.). Water budgets and water residence times were calculated from stable isotope budgets. East Lake has a steep vertical δ¹³C (dissolved inorganic carbon, DIC) gradient, with surface δ¹³C values of up to 5.5‰, largely due to diffusional CO2 losses and photosynthetic carbon withdrawal. Paulina Lake is better mixed, has a lower organic productivity and limited surface CO2 evasion; its δ¹³C (DIC) gradient is small. We theorize that the lakes are fed by different geothermal components as a result of phase separation below East Lake. The gas component (CO2, H2S, Hg) enters East Lake, as indicated by the rising bubble trains in the lake. A residual fluid, depleted in Hg but rich in Si, Fe, carbonate, P and As, enters Paulina Lake. The presence of highly toxic components and the gas-charging of East Lake present natural hazards, which may change when new volcanic activity is initiated, and thus should be monitored.
Small-scale eruptions of basaltic magma occurred at both Ning'er and Tongguan in the central Simao Mesozoic Red Strata Basin (SMRSB) in Quaternary, and these eruption cinder cones are still clearly visible at present. In the meanwhile, earthquakes with magnitude 6 frequently occurred in the Simao-Pu'er earthquake zone, which is also in the center of SMRSB, during the last one hundred years. Significant Neotectonism such as faulting and uplifting, the crust and mantle velocity and the electrical structure in central SMRSB mean that magmatism may still exist in this region today. However, whether crustal magma chambers actually exist or not in Ning'er-Tongguan volcanic zone present day and how magmatism interacts with seismicity in Simao-Pu'er seismic zone are still poorly understood. Here, using the pre-existing and our thermal spring chemical composition data, we estimate geothermal reservoir temperatures of 36 springs in Ning'er-Tongguan volcanic zone and adjacent areas, obtaining the spatial distribution pattern of reservoir temperatures in Ning'er-Tongguan volcanic zone by using Kriging Interpolation Method (KIM). Our data show that there exist two anomalous areas where the reservoir temperatures are above 220°C in the vicinity of Ning'er and Tongguan volcanoes. Combining with deep exploration data such as velocity and electrical structure, our results suggust that there still exist two magma chambers in Ning'er-Tongguan volcanic zone today. The first magma chamber locates in Ning'er town, and the second magma chamber locates near Tongguan volcano, Mojiang, but both Ning'er volcano and Tongguan volcano locate no longer above their today's magma chambers, respectively. These two volcanos drift from their magma chamber about 18km in the opposite directions, suggesting the Babianjiang fault (F2) is of dextral strike-slip fault, which dextral dislocation rate has been being up to 18mm/y since Middle Pleistocene; The frequent and dense moderate-strong earthquake activity in Ning'er areas is closely related to deep magmatism and magma-derived fluids activities; The presence of magma fully decouples the upper crust from the underlying crust and results in stress concentration, and magma-derived fluids activity is beneficial to faulting.
Spring-dominated streams in the Oregon Cascades are often characterized by nearly constant discharge and by peak flows that occur in late summer or fall, several months after the annual snowmelt. A model is presented that can account for the temporal variations of discharge and the delay between snowmelt and the period of peak streamflow. Springs are assumed to be fed by an unconfined aquifer that is recharged by the annual snowmelt. Model results depend primarily on the effective permeability and the dimensions of the aquifer. Four spring-fed streams in the Deschutes River basin in the Oregon Cascades are studied. The effective permeability of the young (
A geochemical investigation of springs near Three Sisters volcanoes was conducted in response to the detection of crustal uplift west of the peaks. Dilute, low-temperature springs near the center of uplift show 3He/4He ratios >=7RA (RA is the ratio in air), and transport in total ˜16 MW of heat and ˜180 g/s of magmatic carbon (as CO2). These anomalous conditions clearly reflect the influence of magma, but they seemingly predate the onset of the present uplift and derive from a previous event. Episodes of intrusion may thus be more common in this area than the age of eruptive vents would imply.
Our conceptual model of the Lassen system is termed a liquid-dominated
hydrothermal system with a parasitic vapor-dominated zone. The essential
feature of this model is that steam and steam-heated discharge at
relatively high altitudes in Lassen Volcanic National Park (LVNP) and
liquid discharge with high chloride concentrations at relatively low
altitudes outside LVNP are both fed by an upflow of high-enthalpy
two-phase fluid within the Park. Liquid flows laterally away from the
upflow area toward the areas of high-chloride discharge, and steam rises
through a vapor-dominated zone to feed the steam and steam-heated
features. Numerical simulations show that several conditions are
necessary for the development of this type of system, including (1)
large-scale topographic relief; (2) an initial period of convective
heating within an upflow zone followed by (3) a change in hydrologic or
geologic conditions that initiates drainage of liquid from portions of
the upflow zone; and (4) low-permeability barriers that inhibit the
movement of cold water into the vapor zone. Simulations of thermal fluid
withdrawal south of LVNP, carried out in order to determine the effects
of such withdrawal on portions of the hydrothermal system within the
Park, generally showed decreases in pressure and liquid saturation
beneath the vapor zone which resulted in temporary increases and
subsequent decreases in the rate of upflow of steam. A generalized
production-injection scenario that could mitigate the effects of
development on both the high-chloride and steam-fed features was
identified.
Significant changes occurred in the chemistry of gases discharged from Nisyros fumaroles in the years, 1997–2001, following a strong seismic crisis. Increasing H2S/CO2 ratios and decreasing CH4/CO2 ratios are attributed to an increased contribution of magmatic fluids to the hydrothermal system. Some fumaroles showed concurrent increases in H2 and CO contents implying increases in temperature and pressure in the upper parts of the hydrothermal system. These changes reinforce the possibility of an increased hazard of hydrothermal eruptions at present with respect to the '90's. Moreover, both the present events and the historical hydrothermal eruptions may represent precursory signals of a new period of volcanic unrest at Nisyros.
Earthquakes cause a spectrum of hydrologic responses such as liquefaction (Casagrande 1936; Seed and Lee 1966; Seed and Idriss 1967; Castro 1975; Kuribayashi and Tatsuoka 1975; Finn 1981; Committee on Earthquake Engineering 1985; Ambraseys 1988; Dobry 1989; Papadopoulos and Lefkopulos 1993; Ishihara 1996; Galli 2000; Hsu and Vucetic 2004; Hazirbaba and Rathje 2004; Wang et al. 2006), water-level changes (Roeloffs 1998; Matsumoto et al. 2003; Brodsky et al. 2003), streamflow increases (Rojstaczer et al. 1995; Manga et al. 2003; Wang, Manga et al. 2004; Wang, Wang et al. 2004) and new hot springs (Earthquake Engineering Research Institute 2004). These responses are variably interpreted as due to either the static or the dynamic effects associated with earthquakes (Manga and Wang forthcoming).
Liquefaction is a major seismic hazard to engineered structures, yet its mechanism has remained a mystery. Several hypotheses have been proposed (Seed and Lee 1966; Committee on Earthquake Engineering 1985; Dobry 1989; Hsu and Vucetic 2004). The first hypothesis is that liquefaction during earthquakes is the consequence of an overall pore-pressure development in saturated soils that undergo undrained consolidation during which the intergranular stress is progressively transferred to the interstitial pore water; if pore pressure increases to the extent that it can bear the weight of the overburden, soil loses strength and behaves like a fluid. A second hypothesis assumes a local redistribution of soil density, even though the overall volume may remain constant; i.e. , during ground shaking, some parts of soils consolidate while other parts loosen up so much that they become contractive. Thus pore pressure eventually increases to the extent that soil loses strength and flow. A third and less-known hypothesis is that high …
Samples of gas and water from thermal springs in Loowit and Step canyons and creeks that drain the crater at Mount St. Helens have been collected since October 2004 to monitor the flux of dissolved magmatic volatiles in the hydrologic system. The changing composition of the waters highlights a trend that began as early as 1994 and includes decreasing SO 4 and Cl concentrations and large increases in HCO 3 . Geochemical models indicate that mineral sources and sinks are not the main controls on the changing water chemis- try, and carbon and helium isotopes indicate that their sources in the gases and waters have remained unchanged during this time. The present-day molar ratios of C, S, and Cl in the springs approximate ratios measured in plume emissions in August 2005 and provide supporting evidence that changes in water chemistry most likely reflect changes in the release rates of sulfur gases, HCl, and CO 2 from the magma and a varying degree of efficiency of gas scrubbing by the overlying water. Results from coupled chemical analyses and discharge measurements on the creeks yield an estimate of the dissolved flux of magmatic HCl, SO 2 , and CO 2 of around 5.2, 4.7, and 22 metric tons per day, respectively.
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.
A model for discharge in spring-fed streams is described and applied to streams in the Oregon Cascades. These streams are assumed to be fed by an unconfined aquifer composed predominantly of quaternary basalts and basaltic andesites. The model is based on the unsteady Boussinesq equation and is characterized by a single parameter, a normalized length scale of the aquifer. Flow in a runoff-dominated stream is used as a proxy for the time-dependent groundwater recharge. Four spring-dominated streams with 50 years of daily discharge records are studied, and modeling efficiencies are in the range of 0.76-0.89. The effective transmissivity is found to be approximately proportional to the length scale of the aquifers. Groundwater recharge rates are in the range of 66-127 cm/yr and 40-73% of the mean annual precipitation.
Images from satellite interferometric synthetic aperture radar (InSAR) reveal uplift of a broad ∼10 km by 20 km area in the Three Sisters volcanic center of the central Oregon Cascade Range, ∼130 km south of Mt. St. Helens. The last eruption in the volcanic center occurred ∼1500 years ago. Multiple satellite images from 1992 through 2000 indicate that most if not all of ∼100 mm of observed uplift occurred between September 1998 and October 2000. Geochemical (water chemistry) anomalies, first noted during 1990, coincide with the area of uplift and suggest the existence of a crustal magma reservoir prior to the uplift. We interpret the uplift as inflation caused by an ongoing episode of magma intrusion at a depth of ∼6.5 km.
Significant increases in helium emissions from the soil and of 3He/4He ratios in groundwater on El Hierro Island (Canary Islands, Spain) were observed prior the 2011–2012 submarine eruption off the coast of the island. The changes of diffusive helium emissions rate were observed one month prior to the submarine eruption onset (October 12, 2011) and the major increase preceded increases in seismic energy release during the volcanic unrest. Measured 3He/4He ratios in groundwaters from a well in El Hierro Island increased from 2 to 3 RA to 7.2 RA one month prior the eruption onset to reach a peak of 8.2 RA (where RA is the 3He/4He ratio in air) indicating a dominant magmatic contribution to the dissolved gases in ground waters. 3He/4He values and diffusive helium emission studies have been extremely important for forecasting the onset of the volcanic unrest and subsequent volcanic eruption. An aseismic exsolution of magmatic gases from magma bodies beneath El Hierro Island through fractures and vertical permeability structures increased the diffusive helium emission rate prior to episodes of seismic-energy release associated to the volcanic unrest.
Images from satellite interferometric synthetic aperture radar (InSAR) reveal uplift of a broad ∼10 km by 20 km area in the Three Sisters volcanic center of the central Oregon Cascade Range, ∼130 km south of Mt. St. Helens. The last eruption in the volcanic center occurred ∼1500 years ago. Multiple satellite images from 1992 through 2000 indicate that most if not all of ∼100 mm of observed uplift occurred between September 1998 and October 2000. Geochemical (water chemistry) anomalies, first noted during 1990, coincide with the area of uplift and suggest the existence of a crustal magma reservoir prior to the uplift. We interpret the uplift as inflation caused by an ongoing episode of magma intrusion at a depth of ∼6.5 km.
Monitoring of quiescent volcanoes, such as Campi Flegrei (Italy), involves the
measurement of geochemical and geophysical parameters that are expected to change as
eruptive conditions approach. Some of these changes are associated with the hydrothermal
activity that is driven by the release of heat and magmatic fluids. This work focuses on
the properties of the porous medium and on their effects on the signals generated by the
circulating fluids. The TOUGH2 porous media flow model is applied to simulate a shallow
hydrothermal system fed by a source of magmatic fluids. The simulated activity of the
source, with periods of increased fluid discharge, generates changes in gas composition,
gravity, and ground deformation. The same boundary conditions and source activity were
applied to simulate the evolution of homogeneous and heterogeneous systems,
characterized by different rock properties. Phase distribution, fluid composition, and the
related signals depend on the nature and properties of the rock sequence through which the
fluids propagate. Results show that the distribution of porosity and permeability affects all
the observable parameters, controlling the timing and the amplitude of their changes
through space and time. Preferential pathways for fluid ascent favor a faster evolution,
with larger changes near permeable channels. Slower changes over wider areas
characterize less permeable systems. These results imply that monitoring signals do not
simply reflect the evolution of the magmatic system: intervening rocks leave a marked
signature that should be taken into account when monitoring data are used to infer
system conditions at depth.
This paper focuses on the role that hydrothermal systems may play in caldera unrest. Changes in the fluid chemistry, temperature and discharge rate of hydrothermal systems are commonly detected at the surface during volcanic unrest, as hydrothermal fluids adjust to changing subsurface conditions. Geochemical monitoring is carried out to observe the evolving system conditions. Circulating fluids can also generate signals that affect geophysical parameters monitored at the surface. Effective hazard evaluation requires a proper understanding of unrest phenomena and correct interpretation of their causes. Physical modelling of fluid circulation allows quantification of the evolution of a hydrothermal system, and hence evaluation of the potential role of hydrothermal fluids during caldera unrest. Modelling results can be compared with monitoring data, and then contribute to the interpretation of the recent caldera evolution. This paper: (1) describes the main features of hydrothermal systems; (2) briefly reviews numerical modelling of heat and fluid flow through porous media; (3) highlights the effects of hydrothermal fluids on unrest processes and (4) describes some model applications to the Phlegrean Fields caldera. Simultaneous modelling of different independent parameters has proved to be a powerful tool for understanding caldera unrest. The results highlight the importance of comprehensive conceptual models that incorporate all the available geochemical and geophysical information, and they also stress the need for high-quality, multi-parameter monitoring and modelling of volcanic activity.
Unrest at collapse calderas is generally thought to be triggered by the arrival of new magma at shallow depth. But few unrest periods at calderas over the past decades have culminated in volcanic eruptions and the role of hydrothermal processes during unrest is drawing more and more attention. Here we report joint and simultaneous continuous multi-parameter observations made at the restless Nisyros caldera (Greece), which reveal non-steady short-term oscillatory signals. The combined geodetic, gravimetric, seismic and electromagnetic records indicate that the oscillations are associated with thermohydromechanical disturbances of the hydrothermal system. The dominant period of oscillation (40-60 min) indicates short-term processes most likely associated with instabilities in the degassing process. Amplitudes of recorded geodetic and gravimetric signals are comparable to amplitudes observed at other periodically restless calderas. We conclude that shallow aqueous fluid migration can contribute significantly to periodic unrest explaining the lack of eruptions in many cases of unrest.
[ 1] We present results from the modeling of ground deformation and microgravimetric data recorded at Campi Flegrei in order to assess the causative phenomena of caldera unrest between 1981 and 2001. We find that residual gravity changes during ground uplift ( 1982 - 1984) are indicative of mass changes in a hybrid of magmatic and hydrothermal sources. During deflation between 1985 and 2001, the inversion of gravity residuals for a single source does not provide convincing results. We then performed the joint inversion of gravity and deformation data for multiple spherical sources and refined source parameters by finite element modeling in order to mitigate against limitations of the analytical solutions. The data recorded during inflation and rapid deflation may be best explained by mass and pressure changes in a deep magmatic source at about 5 km depth and a shallow ( 2 km deep) hydrothermal source. Both sources contribute equally to the gravity changes observed between 1982 and 1984; the contemporary uplift appears to be mainly caused by the shallow source. The subsequent deflation is dominated by a pressure decrease in the hydrothermal source; the magmatic source contributes chiefly to the observed gravity changes. Pressure and density variations within multiple shallow-seated hydrothermal sources provide acceptable fits to the deflation and accompanying gravity changes recorded since 1988. These shallow level dynamics also appear to trigger spatially and temporarily random short-term reversals of the overall mode of ground subsidence since 1985. Our analysis does not support the idea of magmatic contributions to these short-lived periods of inflation.
During the period 1973 to 1991 the interval between eruptions from a periodic geyser in Northern California exhibited precursory variations 1 to 3 days before the three largest earthquakes within a 250-kilometer radius of the geyser. These include the magnitude 7.1 Loma Prieta earthquake of 18 October 1989 for which a similar preseismic signal was recorded by a strainmeter located halfway between the geyser and the earthquake. These data show that at least some earthquakes possess observable precursors, one of the prerequisites for successful earthquake prediction. All three earthquakes were further than 130 kilometers from the geyser, suggesting that precursors might be more easily found around rather than within the ultimate rupture zone of large California earthquakes.
Gas samples collected from the plume consisted mainly of atmospheric air; H2, SO2, and volcanic CO2 were at detectable levels. Gas emitted from crater fumaroles contained H2O, CO2, H2, H2S, SO2, HCl, HF, and some air. Concentrations of H2O, H2, CO2, and CO would have been at chemical equilibrium at temperatures 525oC-650oC. delta 13C values of -10.4 per mil to -10.8 per mil (PDB) indicate that the CO2 may have originated in the mantle. The fumarolic water differs in delta D value (-33 per mil SMOW) and delta 18O value (+5.94 per mil SMOW) from locally derived meteoric water (about -90 per mill in D and -12 per mil in 18O), indicating a deep component in the fumarolic gas. -Authors
An extensive area near the Three Sisters volcanic center, Oregon, has
been actively uplifting since 1996. In this study we use Interferometric
Synthetic Aperture Radar (InSAR) to assess the Three Sisters uplift in
time and space from 1992 through 2010. We present the first InSAR
line-of-sight time series of the deformation, refine the onset of
volcanic intrusive activity, assess the changes in deformation through
time, and determine whether inflation is still occurring. We model InSAR
data to determine the source geometry that best describes the uplift and
create an inflation time series of the deformation. Our results reveal
an intrusion, located at ˜5-7 km depth with a cumulative volume of
magma of ˜5-7 × 107 m3 as of fall
2010. The input of magma started gradually around the summer of 1996,
increased significantly from 1998 to 2003, and then decreased in rate
from 2004 through 2010. We present evidence that a swarm in 2004 was
associated with the decrease in the source inflation rate.
This conceptual model of the Lassen system is termed a liquid-dominated hydrothermal system with a parasitic vapor-dominated zone. The essential feature of this model is that steam and steam-heated discharge at relatively high altitudes in Lassen Volcanic National Park (LVNP) and liquid discharge with high chloride concentrations at relatively low altitudes outside LVNP are both fed by an upflow of high-enthalpy two-phase fluid with the Park. Liquid flows laterally away from the upflow area toward the areas of high-chloride discharge, and steam rises through a vapor-dominated zone to feed the steam and steam-heated features. Numerical simulations show that several conditions are necessary for the development of this type of system, including large-scale topographic relief; an initial period of convective heating within an upflow zone followed by a change in hydrologic or geologic conditions that initiates drainage of liquid from portions of the upflow zone; and low-permeability barriers that inhibit the movement of cold water into the vapor zone. Simulations of thermal fluid withdrawal south of LVNP, carried out in order to determine the effects of such withdrawal on portions of the hydrothermal system within the Park, generally showed decreases in pressure and liquid saturation beneath the vapor zone which resulted in temporary increases and subsequent decreases in the rate of upflow of steam. A generalized production-injection scenario that could mitigate the effects of development on both the high-chloride and steam-fed features was identified.
The author has identified the following significant results. Analysis of LANDSAT 1 MSS images of October 6, 24, and 25 1972 of the Lassen volcanic region, California, revealed the existence of three large geomorphic rings between Lassen Peak and Lake Almanor. Ring 1, about 16 x 33 km and 490 sq km in area, was centered on the North Branch of the North Fork of the Feather River. Ring 2, 18 x 20.5 km and 300 sq km in area, was concentric to and enclosed by ring 1. Ring 3, 23 x 11 km and 230 sq km in area, was centered on Butt Mountain and cuts ring 1 on the south. All three rings consisted of composite curvilineaments that represent geologic features of two categories: (1) geologically mapped structures and volcanic landforms, and (2) landforms and lines of geomorphic origin that were inferred to represent the surface expression of subsurface structures. Stream-valley and lake-shoreline continuations of mapped faults, escarpments, and aligned segments of stream valleys were included in the 2nd category. The rings overlap a gravity low 5300 sq km in area, and might be the surface expression of volcano tectonic collapse structures that followed eruption of voluminous ash flow tuffs beggining in Miocene time.
Carbon dioxide and helium with isotopic compositions indicative of a magmatic source (delta13C=-4.5 to -50/00, 3He/4He=4.5 to 6.7 RA) are discharging at anomalous rates from Mammoth Mountain, on the southwestern rim of the Long Valley caldera in eastern California. The gas is released mainly as diffuse emissions from normal-temperature soils, but some gas issues from steam vents or leaves the mountain dissolved in cold groundwater. The rate of gas discharge increased significantly in 1989 following a 6-month period of persistent earthquake swarms and associated strain and ground deformation that has been attributed to dike emplacement beneath the mountain. An increase in the magmatic component of helium discharging in a steam vent on the north side of Mammoth Mountain, which also began in 1989, has persisted until the present time. Anomalous CO2 discharge from soils first occurred during the winter of 1990 and was followed by observations of several areas of tree kill and/or heavier than normal needlecast the following summer. Subsequent measurements have confirmed that the tree kills arc associated with CO2 concentrations of 30-90% in soil gas and gas flow rates of up to 31,000 gm-2d-1 at the soil surface. Each of the tree-kill areas and one area of CO2 discharge above tree line occurs in close proximity to one or more normal faults, which may provide conduits for gas flow from depth. We estimate that the total diffuse CO2 flux from the mountain is approximately 520 t/d, and that 30-50 t/d of CO2 are dissolved in cold groundwater flowing off the flanks of the mountain. Isotopic and chemical analyses of soil and fumarolic gas demonstrate a remarkable homogeneity in composition, suggesting that the CO2 and associated helium and excess nitrogen may be derived from a common gas reservoir whose source is associated with some combination of magmatic degassing and thermal metamorphism of metasedimentary rocks. Furthermore, N2/Ar ratios and nitrogen isotopic values indicate that the Mammoth Mountain gases are derived from sources separate from those that supply gas to the hydrothermal system within the Long Valley caldera. Various data suggest that the Mammoth Mountain gas reservoir is a large, low-temperature cap over an isolated hydrothermal system, that it predates the 1989 intrusion, and that it could remain a source of gas discharge for some time.
The Loma Prieta (California) earthquake (October 17, 1989; M 7.1) caused significant changes in the hydrology of the San Lorenzo and Pescadero drainage basins, northwest of the epicenter. Streamflow increased at most gauging stations within 15 min after the earthquake. Ionic concentrations and the calcite saturation index of the stream water also increased. Streamflow and solute concentrations decayed significantly over a period of several months following the earthquake. Ground-water levels in the highland parts of the basins were locally lowered by as much as 21 m within weeks to months after the earthquake. The spatial and temporal character of the hydrologic response suggests that the earthquake increased rock permeability and temporarily enhanced ground-water flow rates in the region.
Physical parameters are defined for a flow of water and steam in a
porous medium: dynamic and kinematic viscosity, density, and
compressibility. These permit single-phase pressure transient theory to
be applied to two-phase flow provided that the pressure changes are not
too large.
The hydrothermal system beneath Campi Flegrei, an explosive caldera in
southern Italy, is quantified by analyzing gas samples collected since
1983, during and after 2 years of intense earthquake swarms and dramatic
uplift of the caldera center. These gas samples were obtained from both
land and submarine furmaroles, as well as a few samples from water
wells. At the Bocca Grande fumarole in Solfatara Crater, near the center
of Campi Flegrei, large variations were measured in the amount of water
vapor, hydrogen sulfide, nitrogen and hydrogen gases, methane, and
hydrogen chloride. Some variations could be controlled partly by a
change in heat flux from a deep source to a surficial hydrothermal
system. Possible evidence of a change in heat flux comes from subsurface
temperatures, calculated from a water-carbon monoxide reaction. The
calculated temperatures changed mostly in 1989-1990. Concurrent changes
were measured in concentrations of hydrogen sulfide, nitrogen, and
hydrogen. No change was noted in helium and carbon isotopes, which could
have indicated a change in emission of magmatic gases. I suggest the
changes in gas chemistry since 1985 could be evidence of an aborted
period of unrest, which was characterized as a change in gas emissions
but did not progress far enough to produce uplift or earthquake swarms.
As pointed out by other researchers, the ratio of helium isotopes, which
implies the presence of magma, is uniform across an area that includes
Campi Flegrei. The distribution of carbon isotopes, which is nonuniform,
correlates with limestone outcrops and the presence of shallow thermal
sources.
Rapid multichannel monitoring of fumaroles on Volcan Colima, Mexico, provides new insight into the time-scales and magnitudes of fumarole temperature variation. Temperatures in five fumaroles, all located along a single fracture cutting the summit lava dome of the volcano, were monitored at 20-min intervals between May 1991 and May 1992. Mean fumarole temperatures varied between 350°C and 550°C. Statistical analysis of these time series shows that significant diurnal variation occurs in each fumarole. Simultaneous monitoring of atmospheric pressure at the fumaroles indicates that these variations in temperature are inversely correlated with barometric pressure. A numerical model developed to explore the dependence of fumarole temperature on mass flow demonstrates that many aspects of observed temperature variation are accounted for by mass flow variation, resulting from small changes in barometric pressure. The method described here represents a substantial improvement over traditional fumarole-monitoring techniques because subtle variation can be quickly identified using standard statistical techniques, and the method provides regular information about thermal activity on a volcano, minimizing the hazards normally associated with the collection of these data on a regular basis. -from Authors
We compiled time series of hydrothermal discharge consisting of 3593 chloride- or heat-flux measurements from 24 sites in the Yellowstone region, the northern Oregon Cascades, Lassen Volcanic National Park and vicinity, and Long Valley, California. At all of these sites the hydrothermal phenomena are believed to be as yet unaffected by human activity, though much of the data collection was driven by mandates to collect environmental-baseline data in anticipation of geothermal development. The time series average 19years in length and some of the Yellowstone sites have been monitored intermittently for over 30 years. Many sites show strong seasonality but few show clear long-term trends, and at most sites statistically significant decadal-scale trends are absent. Thus, the data provide robust estimates of advective heat flow ranging from ∼130MW in the north-central Oregon Cascades to ∼6100MW in the Yellowstone region, and also document Yellowstone hydrothermal chloride and arsenic fluxes of 1740 and 15–20g/s, respectively. The discharge time series show little sensitivity to regional tectonic events such as earthquakes or inflation/deflation cycles. Most long-term monitoring to date has focused on high-chloride springs and low-temperature fumaroles. The relative stability of these features suggests that discharge measurements done as part of volcano-monitoring programs should focus instead on high-temperature fumaroles, which may be more immediately linked to the magmatic heat source.
Mount St. Helens has been more active and more explosive during the last 4500 years than any other volcano in the conterminous United States. Eruptions of that period repeatedly formed domes, large volumes of pumice, hot pyroclastic flows, and during the last 2500 years, lava flows. Some of this activity resulted in mudflows that extended tens of kilometers down the floors of valleys that head at the volcano. This report describes the nature of these phenomena and their threat to people and property; the accompanying maps show areas likely to be affected by future eruptions of Mount St. Helens. Explosive eruptions that produce large volumes of pumice affect large areas because winds can carry the lightweight material hundreds of kilometers from the volcano. Because of prevailing winds, the 180° sector east of the volcano will be affected most often and most severely by future eruptions of this kind. However, the pumice from any one eruption probably will fall in only a small part of that sector. Pyroclastic flows and mudflows also can affect areas far from the volcano, but the areas they affect are smaller because they follow valleys. Mudflows and possibly pyroclastic flows moving rapidly down Swift and Pine Creeks could displace water in Swift Reservoir, which could cause disastrous floods farther downvalley.
The author has identified the following significant results. Two thermal anomalies, A at 2740 m altitude on the north slope, and B between 2650 and 2750 m altitude on the southwest slope at the contact of the dacite summit dome of Mount St. Helens, Washington, were confirmed by aerial infrared scanner surveys between 1971 and 1973. LANDSAT 1 data collection platform 6166, emplaced at site B anomaly, transmitted 482 sets of temperature values in 1973 and 1974, suitable for estimating the differential radiant emission as 84 W/sq m, approximately equivalent to the Fourier conductive flux of 89 W/sq m in the upper 15 cm below the surface. The differential geothermal flux, including heat loss via evaporation and convection, was estimated at 376 W/sq m. Total energy yield of Mount St. Helens probably ranges between 0.1 and 0.4 x 10 to the 6th power W.
We have designed and tested a passive headspace sampler for the collection of noble gases that allows for the precise calculation of dissolved gas concentrations from measured gas mixing ratios. Gas permeable silicon tubing allows for gas exchange between the headspace in the sampler volume and the dissolved gases in the adjacent water. After reaching equilibrium, the aqueous-phase concentration is related to the headspace concentration by Henry's law. Gas exchange between the water and headspace can be shut off in situ, preserving the total dissolved gas pressure upon retrieval. Gas samples are then sealed in an all metal container, retaining even highly mobile helium. Dissolved noble gas concentrations measured in these diffusion samplers are in good agreement with traditional copper tube aqueous-phase samples. These significantly reduce the laboratory labor in extracting the gases from a water sample and provide a simple and robust method for collecting dissolved gas concentrations in a variety of aqueous environments.
Separate abstracts were prepared for seven papers. Also included are a bibliography of geothermal resource information for the State of Washington, well temperature information and locations in the State of Washington, and a map of the geology of the White Pass-Tumac Mountain Area, Washington. (MHR)
Temperature measurements over quite a long period (since 1976) at an artesian spring at Usami Hot Springs, which is located on the northeastern coast of the Izu Peninsula (Japan) where there has been considerable seismic activity recently, have revealed that the temperature of this hot spring varies in close relation to the occurrence of earthquakes and volcanic eruptions in this region. The highly accurate measurements that have been carried out continuously since 1982 show the nature of temperature changes in this artesian spring at normal times. Based on this, an examination of the long-term temperature change curve produced the following results: (1) normally, the temperature of this artesian spring falls slowly in a more or less linear manner: (2) at the time of a strong earthquake the temperature jumps suddenly in a step pattern; (3) both the long- and short-term precursory changes in temperature have been observed before large shallow earthquakes that have occurred relatively near to the well. This paper also considers the mechanism behind these temperature changes.
Geochemical studies on cold meteoric waters, post-1980 hot spring waters, fumarole emissions from the dacite dome, and volcanic rocks at Mount St. Helens (MSH) from 1985 to 1989 show that magmatic volatiles are involved in the formation of a new hydrothermal system. Hot spring waters are enriched in 18O by as much as 2 and display enrichments in D relative to cold waters. A well-defined isotopic trend is displayed by the isotopic composition of a>400C fumarole condensate collected from the central crater in 1980 (-33 D, +6 18O), of condensate samples collected on the dome, and of cold meteoric and hot spring waters. The trend indicates that mixing occurs between local meteoric water and magmatic water degassing from the dacite dome. Between 30 and 70% magmatic water is present in the dome fumarole discharges and 10% magnatic water has been added to the waters of the hydrothermal system. Relations between Cl, SO4 and HCO3 indicate that the hot spring waters are immature volcanic waters formed by reaction of rocks with waters generated by absorption of acidic volcanic fluids. In addition, the B/Cl ratios of the spring waters are similar to the B/Cl ratios of the fumarole condensates (0.02), values of 13C in the HCO3 of the hot springs (-9.5 to-13.5) are similar to the magmatic value at MSH (-10.5), and the 3He/4He ratio, relative to air, in a hot spring water is 5.7, suggesting a magmatic origin for this component.
The Roving Automated Rare Gas Analysis (RARGA) lab of Berkeley's Physics Department was deployed in Yellowstone National Park for a 19 week period commencing in June, 1983. During this time 66 gas and water samples representing 19 different regions of hydrothermal activity within and around the Yellowstone caldera were analyzed on site. Routinely, the abundances of five stable noble gases and the isotopic compositions of He, Ne, and Ar were determined for each sample. In a few cases the isotopes of Kr and Xe were also determined and found to be of normal atmospheric constitution.
Seismic analysis and geochemical interpretations provide evidence that two separate hydrothermal cells circulate within the greater Lassen hydrothermal system. One cell originates south to SW of Lassen Peak and within the Brokeoff Volcano depression where it forms a reservoir of hot fluid (235–270 °C) that boils to feed steam to the high-temperature fumarolic areas, and has a plume of degassed reservoir liquid that flows southward to emerge at Growler and Morgan Hot Springs. The second cell originates SSE to SE of Lassen Peak and flows southeastward along inferred faults of the Walker Lane belt (WLB) where it forms a reservoir of hot fluid (220–240 °C) that boils beneath Devils Kitchen and Boiling Springs Lake, and has an outflow plume of degassed liquid that boils again beneath Terminal Geyser. Three distinct seismogenic zones (identified as the West, Middle, and East seismic clusters) occur at shallow depths (< 6 km) in Lassen Volcanic National Park, SW to SSE of Lassen Peak and adjacent to areas of high-temperature (≤ 161 °C) fumarolic activity (Sulphur Works, Pilot Pinnacle, Little Hot Springs Valley, and Bumpass Hell) and an area of cold, weak gas emissions (Cold Boiling Lake). The three zones are located within the inferred Rockland caldera in response to interactions between deeply circulating meteoric water and hot brittle rock that overlies residual magma associated with the Lassen Volcanic Center. Earthquake focal mechanisms and stress inversions indicate primarily N–S oriented normal faulting and E–W extension, with some oblique faulting and right lateral shear in the East cluster. The different focal mechanisms as well as spatial and temporal earthquake patterns for the East cluster indicate a greater influence by regional tectonics and inferred faults within the WLB. A fourth, deeper (5–10 km) seismogenic zone (the Devils Kitchen seismic cluster) occurs SE of the East cluster and trends NNW from Sifford Mountain toward the Devils Kitchen thermal area where fumarolic temperatures are ≤ 123 °C. Lassen fumaroles discharge geothermal gases that indicate mixing between a N2-rich, arc-type component and gases derived from air-saturated meteoric recharge water. Most gases have relatively weak isotopic indicators of upper mantle or volcanic components, except for gas from Sulphur Works where δ13C–CO2, δ34S–H2S, and δ15N–N2 values indicate a contribution from the mantle and a subducted sediment source in an arc volcanic setting.
Long-term changes have occurred in the chemistry, isotopic ratios, and emission rates of gas at Mount Baker volcano following a major thermal perturbation in 1975. In mid-1975 a large pulse in sulfur and carbon dioxide output was observed both in emission rates and in fumarole samples. Emission rates of CO2 and H2S were ∼ 950 and 112 t/d, respectively, in 1975; these decreased to ∼ 150 and < 1 t/d by 2007. During the peak of the activity the C/S ratio was the lowest ever observed in the Cascade Range and similar to magmatic signatures observed at other basaltic–andesite volcanoes worldwide. Increases in the C/S ratio and decreases in the CO2/CH4 ratio since 1975 suggest a long steady trend back toward a more hydrothermal gas signature. The helium isotope ratio is very high (> 7 Rc/RA), but has declined slightly since the mid-1970s, and δ13C–CO2 has decreased by ≥ 1‰ over time. Both trends are expected from a gradually crystallizing magma. While other scenarios are investigated, we conclude that magma intruded the mid- to shallow-crust beneath Mount Baker during the thermal awakening of 1975. Since that time, evidence for fresh magma has waned, but the continued emission of CO2 and the presence of a long-term hydrothermal system leads us to suspect some continuing connection between the surface and deep convecting magma.
The June 1912 eruption of Novarupta filled nearby glacial valleys on the Alaska Peninsula with ash-flow tuff (ignimbrite), and post-eruption observations of thousands of steaming fumaroles led to the name ‘Valley of Ten Thousand Smokes’ (VTTS). By the late 1980s most fumarolic activity had ceased, but the discovery of thermal springs in mid-valley in 1987 suggested continued cooling of the ash-flow sheet. Data collected at the mid-valley springs between 1987 and 2001 show a statistically significant correlation between maximum observed chloride (Cl) concentration and temperature. These data also show a statistically significant decline in the maximum Cl concentration. The observed variation in stream chemistry across the sheet strongly implies that most solutes, including Cl, originate within the area of the VTTS occupied by the 1912 deposits. Numerous measurements of Cl flux in the Ukak River just below the ash-flow sheet suggest an ongoing heat loss of ∼250 MW. This represents one of the largest hydrothermal heat discharges in North America. Other hydrothermal discharges of comparable magnitude are related to heat obtained from silicic magma bodies at depth, and are quasi-steady on a multidecadal time scale. However, the VTTS hydrothermal flux is not obviously related to a magma body and is clearly declining. Available data provide reasonable boundary and initial conditions for simple transient modeling. Both an analytical, conduction-only model and a numerical model predict large rates of heat loss from the sheet 90 years after deposition.
The elemental and isotopic compositions of helium, neon, argon, and xenon in twenty-one CH4-rich natural gas samples from Cretaceous and Devonian reservoirs in the Alberta, Canada, sedimentary basin were measured. In all but a few cases, radiogenic (⁴He, ⁴⁰Ar, and 131–136Xe) and nucleogenic (21,22Ne) isotopes dominated. Based solely on the noble gas composition, two types of natural gas reservoirs are identified. One (Group B) is highly enriched in radiogenic-nucleogenic noble gases and varies little in composition: , , , ~ 0.7 × 10⁻⁹, and (∗ denotes radiogenic or nucleogenic origin; all ⁴He is radiogenic). High nitrogen content with is also characteristic of Group B samples. The remaining samples (Group A) contain a radiogenic-nucleogenic component with a different composition and, relative to Group B samples, the extent of enrichment in this component is less and more variable: , , and .
Potential hazards from future eruptions of Mount St. Helens volcano The volcanic activity and hot springs of Lassen Peak
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As of the end of the 2012 field season, there had been 87 occurrences of local SEDs approximately ≥ 0.001 J m However, based on measurements by Sorey & Colvard (1994) in 1986–1993, Hot Springs Creek advects about half (H ADV = 10.4 AE 2.7 MW) of the heat from Devils Kitchen (H TOT = 21 AE 4 MW). Heat advected by Hot REFERENCES Barringer JW, Johnsson PA (1996) Theoretical considerations and a simple method for measuring alkalinity in low-pH waters by Gran titration: U.S. Geological Survey Water-Resources Investigations Report 89-4029, 36. Bergfeld D, Evans WC, McGee KA, Spicer KR (2008) Pre-and post-eruptive investigations of gas and water samples from Mount St. Helens, Washington, 2002 to 2005. In: A Volcano Rekindled: The Renewed Eruption of Mount St. Helens, 2004– 2006 (eds Sherrod DR, Scott WE, Stauffer PH), pp. 523–42.
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