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Volcano Hazards Program

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There are about 170 potentially active volcanoes in the U.S. The mission of the USGS Volcano Hazards Program is to enhance public safety and minimize social and economic disruption from volcanic unrest and eruption through our National Volcano Early Warning System. We deliver forecasts, warnings, and information about volcano hazards based on a scientific understanding of volcanic behavior.

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Ash-rich plume rises out of Halemaʻumaʻu Crater, Kilauea Volcano Hawaiʻi

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Mount Rainier seen from Puyallup, Washington

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Volcano Watch — The 1969 Maunaulu eruption: 12 lava fountaining episodes

Volcano Watch — The 1969 Maunaulu eruption: 12 lava fountaining episodes

Photo & Video Chronology — January 12, 2026 — Kīlauea episode 40

Photo & Video Chronology — January 12, 2026 — Kīlauea episode 40

Volcano Watch — Hau’oli Makahiki Hou: a round-up of fireworks from Kīlauea’s fountains

Volcano Watch — Hau’oli Makahiki Hou: a round-up of fireworks from Kīlauea’s fountains

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The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements

From 2019 to 2024, gravity surveys were conducted at the Three Sisters volcanic cluster (TSVC), measuring 246 gravity sites using a spring relative gravimeter. We calculated the residual Bouguer anomaly and identified three main zones with negative anomalies, ranging from −4 to −8 mGal, located southwest and west of South Sister, within an area that has been uplifting for the past two...
Authors
Helene Le Mevel, Nathan Lee Andersen, Annika E. Dechert, Josef Dufek
By
Volcano Hazards Program, Volcano Science Center

The anatomy and lethality of the Siberian Traps large igneous province The anatomy and lethality of the Siberian Traps large igneous province

Emplacement of the Siberian Traps large igneous province (LIP) around 252 Ma coincided with the most profound environmental disruption of the past 500 million years. The enormous volume of the Siberian Traps, its ability to generate greenhouse gases and other volatiles, and a temporal coincidence with extinction all suggest a causal link. Patterns of marine and terrestrial extinction...
Authors
Seth D. Burgess, Benjamin A. Black
By
Volcano Hazards Program, Volcano Science Center

Mitigation of human cognitive bias in volcanic eruption forecasting Mitigation of human cognitive bias in volcanic eruption forecasting

Modern operational eruption forecasting methods rely heavily on human judgment in the face of uncertainty and are thus susceptible to myriad cognitive biases and errors by the scientist-forecasters. Recent developments in the behavioral sciences have elucidated cognitive biases across a wide spectrum of human behaviors and found ways to mitigate them. These insights have led to...
Authors
Heather M. Wright, J. D. Pesicek, Stephen A. Spiller
By
Volcano Hazards Program, Volcano Science Center
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Techniques for Melt Inclusion Study

SAMPLE PREPARATION

Any study of MI should be preceded by a detailed field study of the host rocks. In addition, thin sections should be prepared for petrographic analysis of phenocryst phases, modes, rock textures, and phase relationships. Such information is vital to successful interpretation of data obtained through MI analysis.

Optimally, the MI-bearing phenocrysts should be picked from crystal separates. For pumiceous and scoriaceous rocks, such separates are particularly easy to prepare, as the matrix glass may be easily crushed and separated from crystals (often, by simply floating it away). Even for lavas and granites, crystals can be readily separated from groundmass and other phenocryst phases after crushing and use of heavy liquids. Any type of igneous phenocryst may contain MI. Olivine and quartz have been used for most studies because, in contrast to crystals with good cleavage, they tend to survive eruption and sample preparation without fracturing. An additional advantage of quartz is that its homogeneous and constant composition makes data acquisition and reduction quite simple. Pyroxenes, though relatively opaque, also can be used successfully, and MI studies have used plagioclase, sanidine, leucite, apatite and other phases.

Workers should avoid analysis of inclusions in grain mounts and thin sections if the MI were not observed and described prior to polishing. Instead, MI-bearing phenocrysts should be immersed in a mineral oil of appropriate refractive index to minimize scattering of light. Either a petrographic or stereoscopic microscope can be used to view the inclusions, or optimally, a spindle stage (e.g., Anderson & Bodnar 1993). Such setups permit observation of the inclusion in three-dimensions, allowing detection of cracks, capillaries, and other features that may indicate that the inclusion did not remain a closed system during cooling and depressurization (e.g., Fig. 3). Workers should also record inclusion size, shape, and color, and describe any associated bubbles. Afterwards, the MI-bearing crystals can be mounted and polished.

 

ELECTRON MICROPROBE ANALYSIS (EPMA):

Most studies of MI will include major-element analysis by electron microprobe. This technique permits assessment of inclusion composition and heterogeneity and can provide evidence for magma mixing and/or crystal fractionation. EPMA remains the most accurate technique for determining major elements, Cl, F, and S within inclusions. In the past, because of the difficulty in direct analysis of O, most samples have been analyzed and reported as oxides, with the mass of oxygen associated with elemental cations assigned during data reduction. If H2O is present within a mineral or glass sample, this procedure results in reported totals of significantly less than 100% because the electron microprobe is not sensitive to the presence of H. This causes the amounts of both H and O to be under-reported. Anderson (1974b) used this deficit to his advantage in applying the "difference method" (100% minus EPMA analysis total) to estimate the dissolved-water concentrations of MI.

The difference method can be difficult to apply, however, because other factors can contribute to analysis totals less than 100%. Small, low-charge cations such as Na may migrate within the sample during electron-beam analysis, resulting in underestimates of actual abundances (Nielsen & Sigurdsson 1981). The problem increases for glasses, particularly when they are hydrated, and it becomes difficult to assess whether a low total is due to the presence of H2O or reflects a poor analysis. Sodium migration can be minimized by using a low beam current, a large spot size, mean-atomic-number background corrections and by counting Na at the beginning of the analysis. More sophisticated analytical protocols are discussed by Nielsen & Sigurdsson (1981).

Modern availability of synthetic spectrometer crystals permits direct analysis of O, so that the EPMA total for hydrous samples can be close to 100% (Nash 1992). Water concentrations can then be quantified by calculating the amount of oxygen not associated with the other major cationic species, and instead assigning it to H. Analytical uncertainties are similar to the 'difference method' but the technique is preferable because it permits the analyst to be more confident that the calculated H2O concentration is not spurious due to analytical problems such as elemental migration.

 

ION MICROPROBE

Secondary Ion Mass Spectrometry (SIMS; a.k.a. ion microprobe) allows quantification of trace components within very small spots (<20 µm) with detection limits of < 1 ppm for some elements. Several labs have used this technology to analyze silicate MI for a large variety of trace metals as well as the volatile elements F and H (Hervig et al. 1989; Lu et al. 1992; Sisson & Layne 1993; Webster & Duffield 1994). Its greatest advantage is that sample preparation is simple, involving only a singly polished section or grain mount that can be placed on different kinds of sample holders. If well-characterized standards are prepared that are similar to the samples in composition, and backgrounds are minimized, this technique can be both accurate and reproducible. Ihinger et al. (1994) gave a lengthy discussion of the use of SIMS for the analysis of H2O and F in volcanic and synthetic glass.

 

FOURIER TRANSFORM INFRARED (FTIR) SPECTROSCOPY

FTIR is a highly reproducible spectroscopic technique that can be used to quantify the amounts of dissolved H2O and CO2 in glass. Moreover, it provides information about the speciation of H2O (molecular H2O versus hydroxyl) and CO2 (carbonate versus molecular CO2) within the sample. Where calibrations have been performed, as for rhyolite and basalt, the technique is also highly accurate. For other compositions, accuracy is limited to about 20% relative. This technique remains the most reliable method for analysis of H2O and CO2 in MI, though sample preparation is tedious. The inclusion (within its host) must be prepared as a doubly polished wafer that sits upon an aperture through which a collimated (or focused) beam of IR radiation is transmitted. Quantification requires knowledge of the sample thickness and density, as well as the absorption (extinction) coefficient, e, for the species of interest within the glass. Ihinger et al. (1994) give extinction coefficients for H2O and CO2 in a variety of glass compositions and review the pertinent literature on this technique.

 

OTHER ANALYTICAL TECHNIQUES

Although other techniques such as the X-ray microprobe (Lu et al. 1989) and Proton-Induced X-ray Emission (Czamanske et al. 1993) have received less attention, they likely will increase the number of elements that can be analyzed in MI. These two techniques are relatively non-destructive (particularly the former) and can provide information on features beneath the sample surface (bubbles, crystals, etc.; Lowenstern et al. 1991). Quantification with the X-ray microprobe requires accurate knowledge of the sample thickness, and the concentration of at least one element within the sample (usually Fe or Ca). For most natural glasses, both techniques are most sensitive to elements with atomic number >20.

Other promising technologies include the nuclear microprobe (Mosbah et al. 1991) which has been used to analyze H in MI. Laser-ablation ICP-mass spectrometry may also be used for trace-element analyses, though, as yet, no one has used this technique for analysis of glass inclusions.

Micro-analytical dating procedures such as laser-based 40Ar/39Ar geochronology may be used to date individual MI. As discussed above, this technique has the potential to discern the timescale of magma-chamber processes (Bogaard & Schirnick 1994).

 

HEATING STAGE

Hundreds of studies have used a high-temperature heating stage to estimate entrapment temperatures of MI by noting the temperature of homogenization of shrinkage bubbles into the silicate melt (Sobolev & Kostyuk 1975). Ideally, homogenization indicates the minimum possible temperature of crystallization of the host phenocryst (Figs. 4, 5). The theory and methods associated with heating experiments are discussed by Roedder (1984) and Belkin (1994).

Beddoe-Stephens et al. (1983) found that heating-stage experiments gave homogenization temperatures too high to be consistent with magmatic temperatures inferred through other techniques; the difference presumably being due to kinetic factors (see also Lowenstern 1994a). Roedder (1984) described some of the difficulties in attaining useful data from heating-stage experiments. Measured homogenization temperatures may be highly dependent on the heating rate of the stage, as well as the viscosity of the silicate melt and diffusion rates of volatiles within the inclusion. In general, the faster the experiment is performed, the higher the apparent homogenization temperature because the diffusion rates for water and other volatiles are insufficient to allow the bubble to dissolve into the melt within the time frame of the experiment.

Despite their inherent uncertainties, however, heating-stage experiments provide important constraints on magmatic temperatures (Li 1994), allow observation of magmatic fluids under magmatic conditions, and can be used to homogenize crystallized inclusions. Individual heating stage assemblies are discussed in detail in Sobolev & Kostyuk (1975).

 

DATA INTERPRETATION

Once chemical and thermometric data have been collected, it remains necessary to ascertain which analyses contain useful data, and which contain information not relevant to the scope of the study. For example, if the purpose of a study is to determine the pre-eruptive volatile concentration of a magma, data from leaked or fractured inclusions need to be discarded. Because fractures and capillaries may be difficult to detect, some inclusions may yield spurious data. Johnson et al. (1994) described three methods for MI data interpretation: the average approach, the high approach, and the one-by-one approach. In the average approach, all data are combined and the mean value is interpreted as the "correct" volatile concentration. When concerned about leaked inclusions, workers may reject low values and favor a high approach, wherein only the highest volatile concentrations are assumed to be correct. Alternatively, one can use a variety of criteria, including major-element composition, bubble size and geometry, inclusion texture, etc., to choose those inclusions that are thought to yield the most reliable data. Though subjective, this one-by-one approach is more flexible, as each igneous rock will yield populations of MI that formed under different conditions and underwent different cooling and depressurization histories. Criteria for MI selection may differ with each new sample, and the inclusionist thus needs to observe carefully and to describe all inclusions prior to analysis.

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The map displays volcanoes, earthquakes, monitoring instruments, and past lava flows.

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Volcano Hazards Program

Find U.S. Volcano

There are about 170 potentially active volcanoes in the U.S. The mission of the USGS Volcano Hazards Program is to enhance public safety and minimize social and economic disruption from volcanic unrest and eruption through our National Volcano Early Warning System. We deliver forecasts, warnings, and information about volcano hazards based on a scientific understanding of volcanic behavior.

Learn more about NVEWS

Volcano Activity Notifications

Ash-rich plume rises out of Halemaʻumaʻu Crater, Kilauea Volcano Hawaiʻi

USGS Volcano Observatories release regular updates and notifications to communicate increases or decreases in volcanic activity and explain unusual or hazardous circumstances. 

Get Latest Updates

Volcano Hazards Assessments

Mount Rainier seen from Puyallup, Washington

Long-term hazards assessments identify locations at risk from volcanic hazards. They are released as high-resolution hazards-zonation maps with accompanying explanations, which help guide eruption preparedness plans.

View Assessments

U.S. Volcano Observatories

Volcano Observatory staff monitor, research, and issue formal notices of activity for volcanoes in assigned geographic areas. Scientists also assess volcano hazards and work with communities to prepare for volcanic eruptions.

Learn More

News

Volcano Watch — The 1969 Maunaulu eruption: 12 lava fountaining episodes

Volcano Watch — The 1969 Maunaulu eruption: 12 lava fountaining episodes

Photo & Video Chronology — January 12, 2026 — Kīlauea episode 40

Photo & Video Chronology — January 12, 2026 — Kīlauea episode 40

Volcano Watch — Hau’oli Makahiki Hou: a round-up of fireworks from Kīlauea’s fountains

Volcano Watch — Hau’oli Makahiki Hou: a round-up of fireworks from Kīlauea’s fountains

View All

Publications

The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements

From 2019 to 2024, gravity surveys were conducted at the Three Sisters volcanic cluster (TSVC), measuring 246 gravity sites using a spring relative gravimeter. We calculated the residual Bouguer anomaly and identified three main zones with negative anomalies, ranging from −4 to −8 mGal, located southwest and west of South Sister, within an area that has been uplifting for the past two...
Authors
Helene Le Mevel, Nathan Lee Andersen, Annika E. Dechert, Josef Dufek
By
Volcano Hazards Program, Volcano Science Center

The anatomy and lethality of the Siberian Traps large igneous province The anatomy and lethality of the Siberian Traps large igneous province

Emplacement of the Siberian Traps large igneous province (LIP) around 252 Ma coincided with the most profound environmental disruption of the past 500 million years. The enormous volume of the Siberian Traps, its ability to generate greenhouse gases and other volatiles, and a temporal coincidence with extinction all suggest a causal link. Patterns of marine and terrestrial extinction...
Authors
Seth D. Burgess, Benjamin A. Black
By
Volcano Hazards Program, Volcano Science Center

Mitigation of human cognitive bias in volcanic eruption forecasting Mitigation of human cognitive bias in volcanic eruption forecasting

Modern operational eruption forecasting methods rely heavily on human judgment in the face of uncertainty and are thus susceptible to myriad cognitive biases and errors by the scientist-forecasters. Recent developments in the behavioral sciences have elucidated cognitive biases across a wide spectrum of human behaviors and found ways to mitigate them. These insights have led to...
Authors
Heather M. Wright, J. D. Pesicek, Stephen A. Spiller
By
Volcano Hazards Program, Volcano Science Center
View All
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