Raman spectroscopy is widely used to quantify CO2 density in geological fluids, yet acquisition parameters, spectral processing methodologies and densimeter calibrations vary between laboratories. The precision of Raman CO2 measurements, and the broader applicability of densimeters generated for a specific instrument, are still debated. This study describes a series of experiments to investigate the effect of different instrument and acquisition parameters on CO2 densities and their errors that can be performed on different Raman instruments, allowing users to determine analytical best practices. First, we discuss the effect of spectral non-linearity, demonstrating that shifts in the selected acquisition window and the choice of Ne lines used for drift correction can generate a diversity of densimeters on a single instrument. However, our repeat measurements of natural fluid inclusion (FI) standards over ~3 years yield a 1σ variation of <0.01 g cm−3, indicating that when consistent methodologies are applied to calibration data and unknowns, Raman analyses are highly reproducible over many years. We then investigate the effect of parameters such as acquisition time, laser power, and sample positioning on peak fitting errors, rebutting recent suggestions that Raman analyses are associated with large uncertainties in Fermi-diad splitting. We show that although high laser powers greatly improve signal:noise ratios (and thus reduce peak fitting errors), natural fluid inclusions hosted in olivine show changes in calculated density outside analytical error with increasing powers (density changing by ~0 to 0.09 g cm−3 per 10 mW of increased power). The amount of heating of the trapped fluid, and thus the change in density, varies drastically on a sample-by-sample basis, with larger amounts of heating in materials hosting the fluid with high absorption coefficients (melt inclusions, and low Fo olivines). We recommend that users assess the degree of laser heating experienced by their samples and select a laser power that limits density changes to a level that will not compromise the objectives of their study. We also offer practical strategies to optimize signal without raising laser power, noting that small changes in focus and x-y position can greatly increase signal intensity.
Explosive eruptions can disperse ash over hundreds of kilometers, but correlating proximal ignimbrites with distal ash-fall deposits remains challenging when units have similar ages and field characteristics. We studied twelve ignimbrites in the southern Central Andean Volcanic Zone of northern Chile (25–27 °S) using a combination of lithofacies observations, petrography, and mineral chemistry data. We evaluate biotite major-element chemistry as a fingerprinting tool for ignimbrite correlation and compare our results with published data from distal ash-fall deposits in the Coastal Cordillera (~350 km NW of potential sources). Biotite compositions define distinct fields for most units, distinguishing the Río Frío and Vega Helada ignimbrites despite similar lithofacies and ages. Pajonales and Juncalito ignimbrites show similar compositions, ages, and petrography, supporting a close correlation. One distal ash-fall deposit is correlated with the Laguna Verde Ignimbrite based on age and biotite chemistry, whereas another shows only tentative chemical affinity with the Wheelwright Ignimbrite.
In situ microanalysis by X-ray spectrometry is a fundamental geochemical technique for volcanology and the geosciences generally and typically performed using an electron microprobe (EPMA) equipped with wavelength dispersive spectrometers (WDS). The related technique of energy dispersive spectrometry (EDS), implemented using either EPMA or a scanning electron microscope (SEM), offers advantages in throughput, simplicity, and cost, yet has historically been relegated to qualitative tasks. We present a quantitative EDS procedure implemented using a W-source SEM and a moderate size silicon drift EDS detector applied to common volcanic materials. Glass and mineral standard data demonstrate that the accuracy and precision of this method is comparable to EPMA–WDS. We show that electron beam damage can be mitigated in volcanic glass through sample-specific optimizations without the need for a time-dependent intensity correction. Our implementation using a relatively inexpensive instrument can potentially increase the accessibility of high-quality, quantitative X-ray microanalysis of major and minor elements.
The Indonesian Volcanology and Geological Hazard Mitigation Center (PVMBG) has raised the status of Mount Lewotobi Laki-laki to Level IV (AWAS), accompanied by massive eruptive activity with sulphur dioxide (SO2) emissions exceeding 10,000 tons/day and an eruption column about 8,000 meters high. This activity may affect local weather parameters, including surface temperature, sulphate aerosol concentration, cloud optical thickness (COT), and precipitation. To identify the influence, this study applies cross correlation function (CCF) analysis using multi sensor satellite data (OMI, AIRS, MERRA 2, MODIS, GPM). The analysis showed positive correlations with time lags: surface temperature responded after 1 day with r = 0.50, sulphate aerosol after 16 days with r = 0.62, cloud optical thickness after 21 days with r = 0.39, and precipitation after 23 days with r = 0.55. These findings demonstrate the influence of SO2 emissions on local weather and provide valuable insights for mitigation in active regions.
Climate warming is accelerating glacier thinning and altering the mechanics of ice-capped volcanoes. At Sollipulli volcano (Southern Andes), DEM differencing between 1979 and 2013 reveals up to ~300 m of surface lowering and an accelerating, non-linear trend fitted with a quadratic function. Using this relationship, Finite Element Method models were developed to simulate how progressive glacier unloading modifies crustal stresses above a shallow magma reservoir. Results show that accelerated thinning markedly reduces the minimum principal stress at the chamber roof and expands an overlying tensile domain, particularly during late-stage unloading. Magma overpressure amplifies these effects, promoting earlier tensile transitions and greater stress changes. The model reproduces key features of observed ice loss and its mechanical consequences. This study provides the first quantitative assessment of such processes in the Andes, where thick caldera-filling glaciers enhance crustal sensitivity to accelerated ice loss and associated volcanic hazards.
