Geology topics

M.P. Doukas

Publications and source records attributed to M.P. Doukas.

16 recordsLinked to original sources

USGS2011

Gas emissions from failed and actual eruptions from Cook Inlet Volcanoes, Alaska, 1989-2006

Cook Inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled. For the six events studied, mean emission rates for eruptions were ~13,000 t/d CO 2 and 5200 t/d SO 2 , but only ~1200 t/d CO 2 and 500 t/d SO 2 for non-eruptive events (‘failed eruptions’). Statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t/d for CO 2 and SO 2 , respectively. Emission rates greater than 4000 and 2000 t/d for CO 2 and SO 2 , respectively, almost exclusively resulted during eruptive events (the only exception being two measurements at Fourpeaked). While this analysis could suggest that unerupted magmas have lower pre-eruptive volatile contents, we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions, or that magmas from failed eruptions experience less decompression such that the majority of H 2 O remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase (or both). In the majority of unrest and eruption sequences, increases in CO 2 emission relative to SO 2 emission were observed early in the sequence. With time, all events converged to a common molar value of C/S between 0.5 and 2. These geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice (i.e., from 20–35 to ~4–6 km) and perhaps roughly similar initial volatile contents in all cases. Early elevated CO 2 levels that we find at these high-latitude, andesitic arc volcanoes have also been observed at mid-latitude, relatively snow-free, basaltic volcanoes such as Stromboli and Etna. Typically such patterns are attributed to injection and decompression of deep (CO 2 -rich) magma into a shallower chamber and open system degassing prior to eruption. Here we argue that the C/S trends probably represent tapping of vapor-saturated regions with high C/S, and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface. At these volcanoes, however, C/S is often accentuated due to early preferential scrubbing of sulfur gases. The range of equilibrium degassing is consistent with the bulk degassing of a magma with initial CO 2 and S of 0.6 and 0.2 wt.%, respectively, similar to what has been suggested for primitive Redoubt magmas.

Alaska↗

USGS2008

Atmospheric contribution of gas emissions from Augustine volcano, Alaska during the 2006 eruption

Airborne surveillance of gas emissions from Augustine for SO 2 , CO 2 and H 2 S showed no evidence of anomalous degassing from 1990 through May 2005. By December 20, 2005, Augustine was degassing 660 td −1 of SO 2 , and ten times that by January 4, 2006. The highest SO 2 emission rate measured during the 2006 eruption was 8650 td −1 (March 1); for CO 2 , 13000 td −1 (March 9), and H 2 S, 8 td −1 (January 19). Thirty‐four SO 2 measurements were made from December 2005 through 2006, with 9 each for CO 2 and H 2 S. Augustine released 1 × 10 6 tonnes of CO 2 to the atmosphere during 2006, a level similar to the output of a medium‐sized natural gas‐fired power plant, and thus was not a significant contributor of greenhouse gas to the atmosphere compared to anthropogenic sources. Augustine released about 5 × 10 5 tonnes of SO 2 during 2006, similar to that released in 1976 and 1986.

Alaska↗

USGS2006

Puhimau thermal area: a window into the upper east rift zone of Kilauea Volcano, Hawaii?

We report the results of two soil CO 2 efflux surveys by the closed chamber circulation method at the Puhimau thermal area in the upper East Rift Zone (ERZ) of Kilauea volcano, Hawaii. The surveys were undertaken in 1996 and 1998 to constrain how much CO 2 might be reaching the ERZ after degassing beneath the summit caldera and whether the Puhimau thermal area might be a significant contributor to the overall CO 2 budget of Kilauea. The area was revisited in 2001 to determine the effects of surface disturbance on efflux values by the collar emplacement technique utilized in the earlier surveys. Utilizing a cutoff value of 50 g m −2 d −1 for the surrounding forest background efflux, the CO 2 emission rates for the anomaly at Puhimau thermal area were 27 t d −1 in 1996 and 17 t d −1 in 1998. Water vapor was removed before analysis in all cases in order to obtain CO 2 values on a dry air basis and mitigate the effect of water vapor dilution on the measurements. It is clear that Puhimau thermal area is not a significant contributor to Kilauea's CO 2 output and that most of Kilauea's CO 2 (8500 t d −1 ) is degassed at the summit, leaving only magma with its remaining stored volatiles, such as SO 2 , for injection down the ERZ. Because of the low CO 2 emission rate and the presence of a shallow water table in the upper ERZ that effectively scrubs SO 2 and other acid gases, Puhimau thermal area currently does not appear to be generally well suited for observing temporal changes in degassing at Kilauea.

Hawaii↗

USGS2004

Evidence for dike emplacement beneath Iliamna Volcano, Alaska in 1996

Two earthquake swarms, comprising 88 and 2833 locatable events, occurred beneath Iliamna Volcano, Alaska, in May and August of 1996. Swarm earthquakes ranged in magnitude from -0.9 to 3.3. Increases in SO2 and CO2 emissions detected during the fall of 1996 were coincident with the second swarm. No other physical changes were observed in or around the volcano during this time period. No eruption occurred, and seismicity and measured gas emissions have remained at background levels since mid-1997. Earthquake hypocenters recorded during the swarms form a cluster in a previously aseismic volume of crust located to the south of Iliamna's summit at a depth of -1 to 4 km below sea level. This cluster is elongated to the NNW-SSE, parallel to the trend of the summit and southern vents at Iliamna and to the regional axis of maximum compressive stress determined through inversion of fault-plane solutions for regional earthquakes. Fault-plane solutions calculated for 24 swarm earthquakes located at the top of the new cluster suggest a heterogeneous stress field acting during the second swarm, characterized by normal faulting and strike-slip faulting with p-axes parallel to the axis of regional maximum compressive stress. The increase in earthquake rates, the appearance of a new seismic volume, and the elevated gas emissions at Iliamna Volcano indicate that new magma intruded beneath the volcano in 1996. The elongation of the 1996-1997 earthquake cluster parallel to the direction of regional maximum compressive stress and the accelerated occurrence of both normal and strike-slip faulting in a small volume of crust at the top of the new seismic volume may be explained by the emplacement and inflation of a subvertical planar dike beneath the summit of Iliamna and its southern satellite vents. ?? 2003 Elsevier B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS2002

Carbon dioxide emission rate of Kīlauea Volcano: Implications for primary magma and the summit reservoir

We report a CO 2 emission rate of 8500 metric tons per day (t d −1 ) for the summit of Kīlauea Volcano, several times larger than previous estimates. It is based on three sets of measurements over 4 years of synchronous SO 2 emission rates and volcanic CO 2 /SO 2 concentration ratios for the summit correlation spectrometer (COSPEC) traverse. Volcanic CO 2 /SO 2 for the traverse is representative of the global ratio for summit emissions. The summit CO 2 emission rate is nearly constant, despite large temporal variations in summit CO 2 /SO 2 and SO 2 emission rates. Summit CO 2 emissions comprise most of Kīlauea's total CO 2 output (&sim;9000 t d −1 ). The bulk CO 2 content of primary magma determined from CO 2 emission and magma supply rate data is &sim;0.70 wt %. Most of the CO 2 is present as exsolved vapor at summit reservoir depths, making the primary magma strongly buoyant. Turbulent mixing with resident reservoir magma, however, prevents frequent eruptions of buoyant primary magma in the summit region. CO 2 emissions confirm that the magma supply enters the edifice through the summit reservoir. A persistent several hundred parts per million CO 2 anomaly arises from the entry of magma into the summit reservoir beneath a square kilometer area east of Halemaumau pit crater. Since most of the CO 2 in primary magma is degassed in the summit, the summit CO 2 emission rate is an effective proxy for the magma supply rate. Both scrubbing of SO 2 and solubility controls on CO 2 and S in basaltic melt cause high CO 2 /SO 2 in summit emissions and spatially uncorrelated distributions of CO 2 and SO 2 in the summit plume.

Journal of Geophysical Research B: Solid Earth↗

USGS2001

Soil efflux and total emission rates of magmatic CO2 at the horseshoe lake tree kill, mammoth mountain, California, 1995-1999

We report the results of eight soil CO2 efflux surveys by the closed circulation chamber method at the Horseshoe Lake tree kill (HLTK) - the largest tree kill on Mammoth Mountain. The surveys were undertaken from 1995 to 1999 to constrain total HLTK CO2 emissions and to evaluate occasional efflux surveys as a surveillance tool for the tree kills. HLTK effluxes range from 1 to > 10,000 g m -2 day -1 (grams CO2 per square meter per day); they are not normally distributed. Station efflux rates can vary by 7-35% during the course of the 8- to 16-h surveys. Disturbance of the upper 2 cm of ground surface causes effluxes to almost double. Semivariograms of efflux spatial covariance fit exponential or spherical models; they lack nugget effects. Efflux contour maps and total CO2 emission rates based on exponential, spherical, and linear kriging models of survey data are nearly identical; similar results are also obtained with triangulation models, suggesting that the kriging models are not seriously distorted by the lack of normal efflux distributions. In addition, model estimates of total CO2 emission rates are relatively insensitive to the measurement precision of the efflux rates and to the efflux value used to separate magmatic from forest soil sources of CO2. Surveys since 1997 indicate that, contrary to earlier speculations, a termination of elevated CO2 emissions at the HLTK is unlikely anytime soon. The HLTK CO2 efflux anomaly fluctuated greatly in size and intensity throughout the 1995-1999 surveys but maintained a N-S elongation, presumably reflecting fault control of CO2 transport from depth. Total CO2 emission rates also fluctuated greatly, ranging from 46 to 136 t day-1 (metric tons CO2 per day) and averaging 93 t day-1. The large inter-survey variations are caused primarily by external (meteorological) processes operating on time scales of hours to days. The externally caused variations can mask significant changes occurring at depth; a striking example is the masking of a degassing event generated at depth and detected by a soil gas sensor network in September 1997 while an efflux survey was in progress. Thus, occasional efflux surveys are not an altogether effective surveillance tool for the HLTK, and making them effective by greatly increasing their frequency may not be practical. Published by Elsevier Science B.V.

Chemical Geology↗

USGS2001

Quiescent hydrogen sulfide and carbon dioxide degassing from Mount Baker, Washington

Volcanic H2S emission rate data are scant despite their importance in understanding magma degassing. We present results from direct airborne plume measurements of H2S and CO2 on a 21-orbit survey at eleven different altitudes around Mount Baker volcano in September 2000 utilizing instrumentation mounted in a light aircraft. Measured emission rates of H2S and CO2 were 5.5 td-1 and 187 td-1 respectively. Maximum concentrations of H2S and CO2 encountered within the 4-km-wide plume were 75 ppb and 2 ppm respectively. Utilizing the H2S signal as a marker for the plume allows the corresponding CO2 signal to be more easily and accurately distinguished from ambient CO2 background. This technique is sensitive enough for monitoring weakly degassing volcanoes in a pre-eruptive condition when scrubbing by hydrothermal fluid or aquifers might mask the presence of more acid magmatic gases such as SO2.

Geophysical Research Letters↗

USGS2000

Geochemical evidence for a magmatic CO 2 degassing event at Mammoth Mountain, California, September-December 1997

Recent time series soil CO 2 concentration data from monitoring stations in the vicinity of Mammoth Mountain, California, reveal strong evidence for a magmatic degassing event during the fall of 1997 lasting more than 2 months. Two sensors at Horseshoe Lake first recorded the episode on September 23, 1997, followed 10 days later by a sensor on the north flank of Mammoth Mountain. Direct degassing from shallow intruding magma seems an implausible cause of the degassing event, since the gas released at Horseshoe Lake continued to be cold and barren of other magmatic gases, except for He. We suggest that an increase in compressional strain on the area south of Mammoth Mountain driven by movement of major fault blocks in Long Valley caldera may have triggered an episode of increased degassing by squeezing additional accumulated CO 2 from a shallow gas reservoir to the surface along faults and other structures where it could be detected by the CO 2 monitoring network. Recharge of the gas reservoir by CO 2 emanating from the deep intrusions that probably triggered deep long-period earthquakes may also have contributed to the degassing event. The nature of CO 2 discharge at the soil-air interface is influenced by the porous character of High Sierra soils and by meteorological processes. Solar insolation is the primary source of energy for the Earth atmosphere and plays a significant role in most diurnal processes at the Earth surface. Data from this study suggest that external forcing due largely to local orographic winds influences the fine structure of the recorded CO 2 signals.

California↗

USGS1998

Three-year decline of magmatic CO2 emissions from soils of a Mammoth Mountain tree kill: Horseshoe Lake, CA, 1995-1997

We used the closed chamber method to measure soil CO 2 efflux over a three-year period at the Horseshoe Lake tree kill (HLTK)—the largest tree kill on Mammoth Mountain in central eastern California. Efflux contour maps show a significant decline in the areas and rates of CO 2 emission from 1995 to 1997. The emission rate fell from 350 t d −1 (metric tons per day) in 1995 to 130 t d −1 in 1997. The trend suggests a return to background soil CO 2 efflux levels by early to mid 1999 and may reflect exhaustion of CO 2 in a deep reservoir of accumulated gas and/or mechanical closure or sealing of fault conduits transmitting gas to the surface. However, emissions rose to 220 t d −1 on 23 September 1997 at the onset of a degassing event that lasted until 5 December 1997. Recent reservoir recharge and/or extension-enhanced gas flow may have caused the degassing event.

Geophysical Research Letters↗

USGS1994

Emission rates of sulfur dioxide and carbon dioxide from Redoubt Volcano, Alaska during the 1989-1990 eruptions

Airborne measurements of sulfur dioxide emission rates in the gas plume emitted from fumaroles in the summit crater of Redoubt Volcano were started on March 20, 1990 using the COSPEC method. During the latter half of the period of intermittent dome growth and destruction, between March 20 and mid-June 1990, sulfur dioxide emission rates ranged from approximately 1250 to 5850 t/d, rates notably higher than for other convergent-plate boundary volcanoes during periods of active dome growth. Emission rates following the end of dome growth from late June 1990 through May 1991 decreased steadily to less than 75 t/d. The largest mass of sulfur dioxide was released during the period of explosive vent clearing when explosive degassing on December 14-15 injected at least 175,000 ?? 50,000 tonnes of SO2 into the atmosphere. Following the explosive eruptions of December 1989, Redoubt Volcano entered a period of intermittent dome growth from late December 1989 to mid-June 1990 during which Redoubt emitted a total mass of SO2 ranging from 572,000 ?? 90,000 tonnes to 680,000 ?? 90,000 tonnes. From mid-June 1990 through May 1991, the volcano was in a state of posteruption degassing into the troposphere, producing approximately 183,000 ?? 50,000 tonnes of SO2. We estimate that Redoubt Volcano released a minimum mass of sulfur dioxide of approximately 930,000 tonnes. While COSPEC data were not obtained frequently enough to enable their use in eruption prediction, SO2 emission rates clearly indicated a consistent decline in emission rates between March through October 1990 and a continued low level of emission rates through the first half of 1991. Values from consecutive daily measurements of sulfur dioxide emission rates spanning the March 23, 1990 eruption decreased in the three days prior to eruption. That decrease was coincident with a several-fold increase in the frequency of shallow seismic events, suggesting partial sealing of the magma conduit to gas loss that resulted in pressurization of the shallow magma system and an increase in earthquake activity. Unlike the short-term SO2 decrease in March 1990, the long-term decrease of sulfur dioxide emission rates from March 1990 through May 1991 was coincident with low rates of seismic energy release and was interpreted to reflect gradual depressurization of the shallow magma reservoir. The long-term declines in seismic energy release and in SO2 emission rates led AVO scientists to conclude on April 19, 1991 that the potential for further eruptive activity from Redoubt Volcano had diminished, and on this basis, the level of concern color code for the volcano was changed from code yellow (Volcano is restless; earthquake activity is elevated; activity may include extrusion of lava) to code green (Volcano is in its normal 'dormant' state). ?? 1994.

Journal of Volcanology and Geothermal Research↗

USGS1993