2.2 Volcanic ash cloud composition
The rock, mineral, and glass particles that make up volcanic ash are expelled by a volcano during an eruption. The particles are under 2 mm in diameter. Rock shards, mineral crystals, and volcanic glass all make up volcanic ash. The composition of volcanic ash is determined by the chemistry of the magma from which it generally formed. It has not been established that most of the minerals found in ash are harmful to human health. Volcanic ash’s chemical makeup changes according to the kind of volcano and the minerals contained in the magma. In general, from a stratovolcano volcano, volcanic ash is composed of roughly 65% SiO2, 18% Al2O3, 5% Fe2O3, 2% MgO, 4% CaO, 4% Na2O, and 0.1% S. In addition to these primary components, 37 trace metals have been identified, including Ba, Cu, Mn, Sr, V, Zn, and Zr. Volcanic ash contains fundamental minerals such as quartz and tridymite, as well as secondary minerals such as kaolin-group minerals and alunite. Volcanic ash’s physical and chemical characteristics are largely influenced by the eruption style. Basaltic air-borne pyroclastic materials have a silica content ranging from 45 to 53.5%, intermediate (andesitic) air-borne pyroclastic materials have a silica content ranging from 53.5 to 62%, and felsic (dacitic and rhyolitic) air-borne pyroclastic materials have a silica content of greater than 62%.
In case of submarine volcanoes, they dump massive amounts of stuff into the oceans, including ash. Volcanic ash has long been detected in marine sediment, and its chemical composition can be utilized to estimate the chemical composition of undersea volcanic ash. One strategy is to quantify distributed volcanic ash in marine sand using geochemical methods. Another method is to use the chemical makeup of volcanic ash deposits to determine their origin.
Scientists developed a relationship between the color and chemical content of discoloured seawater in the vicinity of an underwater volcano. This approach, however, may not be suitable for identifying the chemical composition of undersea volcanic ash. Microbial communities found in sediments differ greatly from those found in hydrothermal fluids. Volcanic ash, such as that seen in the Kermadec arc, is a kind of sediment formed by explosive eruptions. Scientists evaluated microbial community compositions and functioning in two hydrothermal fluid and one tephra (volcanic ash deposit) samples taken from the Kermadec arc in research published in Frontiers in Microbiology. The study discovered that characteristics influencing community structure and element cycling have a significant influence on local element cycling, such as sulphur and nitrogen cycling, Fe-S-mineral precipitation, and the employment of iron (III) as an electron acceptor. Generally, knowing the chemical composition of undersea volcanic ash necessitates the use of geochemical approaches or pinpointing its origins through chemical composition.
2.3 Volcanic ash particle monitoring
For the purpose of identifying and tracking volcanic eruptions and ash in the atmosphere, satellite sensors are crucial. The Advanced Baseline Imager (ABI) on GOES-16 and GOES-17 is the principal surveillance instrument for volcanic clouds. VAAC forecasters utilize ABI data to track clouds whose position, evolution, and/or spectral features correspond to volcanic activity. Volcanic ash detection and monitoring are crucial for ensuring safety and reducing economic damage. The height of a volcanic cloud indicates the severity of an explosive event. Flight level (FL) represents the top of a laterally expanding volcanic cloud and is used to report volcanic cloud height. Researchers examine the average volcanic ash cloud height per occurrence in comparison to that allocated by the M-ESP database to determine how the activity recorded within Volcanic Ash Advisory Areas (VAAs) relates to predicted activity for a specific volcano.
In addition to satellite sensors, a strategy for increased detection of airborne volcanic ash has been developed based on visible (VIS), near-infrared (NIR), shortwave infrared (SWIR), mid-wave infrared (MWIR), long-wave infrared (LWIR), ultraviolet (UV), microwave radiometry, lidar, radar, or combinations thereof. Remote sensing technology is used by satellite sensors to detect volcanic ash. For nearly 20 years, the split window or reverse absorption approach has been employed. The brightness temperatures recorded using two distinct wavelengths of infrared light, which react differently when they travel through clouds of volcanic ash or water droplets, are compared in this approach. Volcanic cloud monitoring is frequently done using the SEVIRI sensor on Meteosat Second Generation (MSG) geostationary satellites. It has a spatial resolution of 3 km at the equator and 4.5 km in Mediterranean latitudes, and it measures radiances in 12 spectral channels spanning the visible to infrared spectrums. Thermal infrared remote sensing can identify volcanic ash clouds fast and precisely. Unfortunately, the inter-band correlations in remote sensing data are rather significant, making it difficult to discern between different types of land cover and atmospheric conditions. Researchers have created algorithms that employ numerous sensors, including lidar and radar data, as well as thermal infrared data from satellites, to improve the accuracy of airborne volcanic ash detection. These algorithms can offer more precise data on the position, height, and concentration of volcanic ash clouds.