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.