Volcanic ash

Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter.[1] The term volcanic ash is also often loosely used to refer to all explosive eruption products (correctly referred to as tephra), including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the escaping gas shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometers away.

Due to its wide dispersal, ash can have a number of impacts on society, including human and animal health, disruption to aviation, disruption to critical infrastructure (e.g., electric power supply systems, telecommunications, water and waste-water networks, transportation), primary industries (e.g., agriculture), buildings and structures.

Plume from eruption of Chaiten volcano, Chile
Ash cloud from the 2008 eruption of Chaitén volcano, Chile, stretching across Patagonia from the Pacific to the Atlantic Ocean.
Eyjafjallajokull-April-17
Ash plume rising from Eyjafjallajökull on April 17, 2010.
DC-10-30 resting on its tail due to Pinatubo ashfall
Volcanic ash deposits on a parked McDonnell-Douglas DC-10-30 during the 1991 eruption of Mount Pinatubo, causing the aircraft to rest on its tail. While falling ash behaves in a similar manner to snow, the sheer weight of deposits can cause serious damage to buildings and vehicles, as seen here, where the deposits were able to cause the 120 ton airliner's centre of gravity to shift.

Formation

Vulkaanilise tuha kiht
454 million-year-old volcanic ash between layers of limestone in the catacombs of Peter the Great's Naval Fortress in Estonia near Laagri. This is a remnant of one of the oldest large eruptions preserved. The diameter of the black camera lens cover is 58 mm (2.3 in).

Volcanic ash is formed during explosive volcanic eruptions, phreatomagmatic eruptions and during transport in pyroclastic density currents.

Explosive eruptions occur when magma decompresses as it rises, allowing dissolved volatiles (dominantly water and carbon dioxide) to exsolve into gas bubbles.[2] As more bubbles nucleate a foam is produced, which decreases the density of the magma, accelerating it up the conduit. Fragmentation occurs when bubbles occupy ~70–80 vol% of the erupting mixture.[3] When fragmentation occurs, violently expanding bubbles tear the magma apart into fragments which are ejected into the atmosphere where they solidify into ash particles. Fragmentation is a very efficient process of ash formation and is capable of generating very fine ash even without the addition of water.[4]

Volcanic ash is also produced during phreatomagmatic eruptions. During these eruptions fragmentation occurs when magma comes into contact with bodies of water (such as the sea, lakes and marshes) groundwater, snow or ice. As the magma, which is significantly hotter than the boiling point of water, comes into contact with water an insulating vapor film forms (Leidenfrost effect).[5] Eventually this vapor film will collapse leading to direct coupling of the cold water and hot magma. This increases the heat transfer which leads to the rapid expansion of water and fragmentation of the magma into small particles which are subsequently ejected from the volcanic vent. Fragmentation causes an increase in contact area between magma and water creating a feedback mechanism,[5] leading to further fragmentation and production of fine ash particles.

Pyroclastic density currents can also produce ash particles. These are typically produced by lava dome collapse or collapse of the eruption column.[6] Within pyroclastic density currents particle abrasion occurs as particles interact with each other resulting in a reduction in grain size and production of fine grained ash particles. In addition, ash can be produced during secondary fragmentation of pumice fragments, due to the conservation of heat within the flow.[7] These processes produce large quantities of very fine grained ash which is removed from pyroclastic density currents in co-ignimbrite ash plumes.

Physical and chemical characteristics of volcanic ash are primarily controlled by the style of volcanic eruption.[8] Volcanoes display a range of eruption styles which are controlled by magma chemistry, crystal content, temperature and dissolved gases of the erupting magma and can be classified using the volcanic explosivity index (VEI). Effusive eruptions (VEI 1) of basaltic composition produce <105 m3 of ejecta, whereas extremely explosive eruptions (VEI 5+) of rhyolitic and dacitic composition can inject large quantities (>109 m3) of ejecta into the atmosphere. Another parameter controlling the amount of ash produced is the duration of the eruption: the longer the eruption is sustained, the more ash will be produced. For example, the second phase of the 2010 eruptions of Eyjafjallajökull was classified as VEI 4 despite a modest 8 km high eruption column, but the eruption continued for a month, which allowed a large volume of ash to be ejected into the atmosphere.

Properties

Chemical

The types of minerals present in volcanic ash are dependent on the chemistry of the magma from which it erupted. Considering that the most abundant elements found in silicate magma are silicon and oxygen, the various types of magma (and therefore ash) produced during volcanic eruptions are most commonly explained in terms of their silica content. Low energy eruptions of basalt produce a characteristically dark coloured ash containing ~45–55% silica that is generally rich in iron (Fe) and magnesium (Mg). The most explosive rhyolite eruptions produce a felsic ash that is high in silica (>69%) while other types of ash with an intermediate composition (e.g., andesite or dacite) have a silica content between 55–69%.

The principal gases released during volcanic activity are water, carbon dioxide, sulfur dioxide, hydrogen, hydrogen sulfide, carbon monoxide and hydrogen chloride.[9] These sulfur and halogen gases and metals are removed from the atmosphere by processes of chemical reaction, dry and wet deposition, and by adsorption onto the surface of volcanic ash.

It has long been recognised that a range of sulfate and halide (primarily chloride and fluoride) compounds are readily mobilised from fresh volcanic ash.;[10][11][12] It is considered most likely that these salts are formed as a consequence of rapid acid dissolution of ash particles within eruption plumes, which is thought to supply the cations involved in the deposition of sulfate and halide salts.

While some 55 ionic species have been reported in fresh ash leachates[9] the most abundant species usually found are the cations Na+, K+, Ca2+ and Mg2+ and the anions Cl, F and SO42−.[9][12] Molar ratios between ions present in leachates suggest that in many cases these elements are present as simple salts such as NaCl and CaSO4.[9][13][14][15] In a sequential leaching experiment on ash from the 1980 eruption of Mount St. Helens, chloride salts were found to be the most readily soluble, followed by sulfate salts[13] Fluoride compounds are in general only sparingly soluble (e.g., CaF2, MgF2), with the exception of fluoride salts of alkali metals and compounds such as calcium hexafluorosilicate (CaSiF6).[16] The pH of fresh ash leachates is highly variable, depending on the presence of an acidic gas condensate (primarily as a consequence of the gases SO2, HCl and HF in the eruption plume) on the ash surface.

The crystalline-solid structure of the salts act more as an insulator than a conductor.[17][18][19][20] However, once the salts are dissolved into a solution by a source of moisture (e.g., fog, mist, light rain, etc.), the ash may become corrosive and electrically conductive. A recent study has shown that the electrical conductivity of volcanic ash increases with (1) increasing moisture content, (2) increasing soluble salt content, and (3) increasing compaction (bulk density).[20] The ability of volcanic ash to conduct electric current has significant implications for electric power supply systems.

Physical

Components

Ashsem small
Particle of volcanic ash from Mount St. Helens.

Volcanic ash particles erupted during magmatic eruptions are made up of various fractions of vitric (glassy, non-crystalline), crystalline or lithic (non-magmatic) particles. Ash produced during low viscosity magmatic eruptions (e.g., Hawaiian and Strombolian basaltic eruptions) produce a range of different pyroclasts dependent on the eruptive process. For example, ash collected from Hawaiian lava fountains consists of sideromelane (light brown basaltic glass) pyroclasts which contain microlites (small quench crystals, not to be confused with the rare mineral microlite) and phenocrysts. Slightly more viscous eruptions of basalt (e.g., Strombolian) form a variety of pyroclasts from irregular sideromelane droplets to blocky tachylite (black to dark brown microcrystalline pyroclasts). In contrast, most high-silica ash (e.g. rhyolite) consists of pulverised products of pumice (vitric shards), individual phenocrysts (crystal fraction) and some lithic fragments (xenoliths).[21]

Ash generated during phreatic eruptions primarily consists of hydrothermally altered lithic and mineral fragments, commonly in a clay matrix. Particle surfaces are often coated with aggregates of zeolite crystals or clay and only relict textures remain to identify pyroclast types.[21]

Morphology

MtStHelensAsh1980eruption
Light microscope image of ash from the 1980 eruption of Mount St. Helens, Washington.

The morphology (shape) of volcanic ash is controlled by a plethora of different eruption and kinematic processes.[21][22] Eruptions of low-viscosity magmas (e.g., basalt) typically form droplet shaped particles. This droplet shape is, in part, controlled by surface tension, acceleration of the droplets after they leave the vent, and air friction. Shapes range from perfect spheres to a variety of twisted, elongate droplets with smooth, fluidal surfaces.[22]

The morphology of ash from eruptions of high-viscosity magmas (e.g., rhyolite, dacite, and some andesites) is mostly dependent on the shape of vesicles in the rising magma before disintegration. Vesicles are formed by the expansion of magmatic gas before the magma has solidified. Ash particles can have varying degrees of vesicularity and vesicular particles can have extremely high surface area to volume ratios.[21] Concavities, troughs, and tubes observed on grain surfaces are the result of broken vesicle walls.[22] Vitric ash particles from high-viscosity magma eruptions are typically angular, vesicular pumiceous fragments or thin vesicle-wall fragments while lithic fragments in volcanic ash are typically equant, or angular to subrounded. Lithic morphology in ash is generally controlled by the mechanical properties of the wall rock broken up by spalling or explosive expansion of gases in the magma as it reaches the surface.

The morphology of ash particles from phreatomagmatic eruptions is controlled by stresses within the chilled magma which result in fragmentation of the glass to form small blocky or pyramidal glass ash particles.[21] Vesicle shape and density play only a minor role in the determination of grain shape in phreatomagmatic eruptions. In this sort of eruption, the rising magma is quickly cooled on contact with ground or surface water. Stresses within the "quenched" magma cause fragmentation into five dominant pyroclast shape-types: (1) blocky and equant; (2) vesicular and irregular with smooth surfaces; (3) moss-like and convoluted; (4) spherical or drop-like; and (5) plate-like.

Density

The density of individual particles varies with different eruptions. The density of volcanic ash varies between 700–1200 kg/m3 for pumice, 2350–2450 kg/m3 for glass shards, 2700–3300 kg/m3 for crystals, and 2600–3200 kg/m3 for lithic particles.[23] Since coarser and denser particles are deposited close to source, fine glass and pumice shards are relatively enriched in ash fall deposits at distal locations.[24] The high density and hardness (~5 on the Mohs Hardness Scale) together with a high degree of angularity, make some types of volcanic ash (particularly those with a high silica content) very abrasive.

Grain size

Volcanic ash grain size distributions
Volcanic ash grain size distributions.

Volcanic ash consists of particles (pyroclasts) with diameters <2 mm (particles >2 mm are classified as lapilli),[1] and can be as fine as 1 μm.[8] The overall grain size distribution of ash can vary greatly with different magma compositions. Few attempts have been made to correlate the grain size characteristics of a deposit with those of the event which produced it, though some predictions can be made. Rhyolitic magmas generally produce finer grained material compared to basaltic magmas, due to the higher viscosity and therefore explosivity. The proportions of fine ash are higher for silicic explosive eruptions, probably because vesicle size in the pre-eruptive magma is smaller than those in mafic magmas.[1] There is good evidence that pyroclastic flows produce high proportions of fine ash by communition and it is likely that this process also occurs inside volcanic conduits and would be most efficient when the magma fragmentation surface is well below the summit crater.[1]

Dispersal

MountRedoubtEruption
Ash plume rising from Mount Redoubt after an eruption on April 21, 1990.
MtCleveland ISS013-E-24184
Ash plume from Mt Cleveland, a stratovolcano in the Aleutian Islands.

Ash particles are incorporated into eruption columns as they are ejected from the vent at high velocity. The initial momentum from the eruption propels the column upwards. As air is drawn into the column, the bulk density decreases and it starts to rise buoyantly into the atmosphere.[6] At a point where the bulk density of the column is the same as the surrounding atmosphere, the column will cease rising and start moving laterally. Lateral dispersion is controlled by prevailing winds and the ash may be deposited hundreds to thousands of kilometres from the volcano, depending on eruption column height, particle size of the ash and climatic conditions (especially wind direction and strength and humidity).[25]

Ash fallout occurs immediately after the eruption and is controlled by particle density. Initially, coarse particles fall out close to source. This is followed by fallout of accretionary lapilli, which is the result of particle agglomeration within the column.[26] Ash fallout is less concentrated during the final stages as the column moves downwind. This results in an ash fall deposit which generally decreases in thickness and grain size exponentially with increasing distance from the volcano.[27] Fine ash particles may remain in the atmosphere for days to weeks and be dispersed by high-altitude winds. These particles can impact on the aviation industry (refer to impacts section) and, combined with gas particles, can affect global climate.

Volcanic ash plumes can form above pyroclastic density currents, these are called co-ignimbrite plumes. As pyroclastic density currents travel away from the volcano, smaller particles are removed from the flow by elutriation and form a less dense zone overlying the main flow. This zone then entrains the surrounding air and a buoyant co-ignimbrite plume is formed. These plumes tend to have higher concentrations of fine ash particles compared to magmatic eruption plumes due to the abrasion within the pyroclastic density current.[1]

Impacts

Introduction

Population growth has caused the progressive encroachment of urban development into higher risk areas, closer to volcanic centres, increasing the human exposure to volcanic ash fall events.

Infrastructure is critical to supporting modern societies, particularly in urban areas, where high population densities create high demand for services. These infrastructure networks and systems support urban living, and provide lifeline services upon which we depend for our health, education, transport and social networking. Infrastructure networks and services support a variety of facilities across a broad range of sectors.[28]

Volcanic ash fall events can disrupt and or damage the infrastructure upon which society depends. Several recent eruptions have illustrated the vulnerability of urban areas that received only a few millimetres or centimetres of volcanic ash.[29][30][31][32][33][34][35] This has been sufficient to cause disruption of transportation, electricity, water, sewage and storm water systems. Costs have been incurred from business disruption, replacement of damaged parts and insured losses. Ash fall impacts on critical infrastructure can also cause multiple knock-on effects, which may disrupt many different sectors and services.

Volcanic ash fall is physically, socially, and economically disruptive. Volcanic ash can affect both proximal areas and areas many hundreds of kilometres from the source, and causes disruptions and losses in a wide variety of different infrastructure sectors. Impacts are dependent on: ash fall thickness; the duration of the ash fall; the grain size and chemistry of the ash; whether the ash is wet or dry; and any preparedness, management and prevention (mitigation) measures employed to reduce effects from the ash fall. Different sectors of infrastructure and society are affected in different ways and are vulnerable to a range of impacts or consequences. These are discussed in the following sections.

Infrastructure sectors

Electricity

Electrical insulator flashover from volcanic ash
Electrical insulator flashover caused by volcanic ash contamination.

Volcanic ash can cause disruption to electric power supply systems at all levels of power generation, transformation, transmission and distribution. There are four main impacts arising from ash-contamination of apparatus used in the power delivery process:[36]

  • Wet deposits of ash on high voltage insulators can initiate a leakage current (small amount of current flow across the insulator surface) which, if sufficient current is achieved, can cause ‘flashover’ (the unintended electrical discharge around or over the surface of an insulating material).

If the resulting short-circuit current is high enough to trip the circuit breaker then disruption of service will occur. Ash-induced flashover across transformer insulation (bushings) can burn, etch or crack the insulation irreparably and will likely result in the disruption of power supply.

  • Volcanic ash can erode, pit and scour metallic apparatus, particularly moving parts such as water and wind turbines and cooling fans on transformers or thermal power plants.
  • The high bulk density of some ash deposits can cause line breakage and damage to steel towers and wooden poles due to ash loading. This is most hazardous when the ash and/or the lines and structures are wet (e.g., by rainfall) and there has been ≥10 mm of ash fall. Fine-grained ash (e.g., <0.5 mm diameter) adheres to lines and structures most readily. Volcanic ash may also load overhanging vegetation, causing it to fall onto lines. Snow and ice accumulation on lines and overhanging vegetation further increases the risk of breakage and or collapse of lines and other hardware.
  • Controlled outages of vulnerable connection points (e.g., substations) or circuits until ash fall has subsided or for de-energised cleaning of equipment.

Drinking water supplies

Following an eruption, it is very common for the public to hold fears about chemical contamination of water supplies. However, in general, the physical impacts of an ashfall will tend to overwhelm problems caused by the release of chemical contaminants from fresh volcanic ash. Impacts vary according to the type of treatment system.

Water turbine eroded by volcanic ash
Water turbine from the Agoyan Hydroelectric plant eroded by volcanic ash laden water.

Groundwater-fed systems are resilient to impacts from ashfall, although airborne ash can interfere with the operation of well-head pumps. Electricity outages caused by ashfall can also disrupt electrically powered pumps if there is no backup generation.

For surface water sources such as lakes and reservoirs, the volume available for dilution of ionic species leached from ash is generally large. The most abundant components of ash leachates (Ca, Na, Mg, K, Cl, F and SO4) occur naturally at significant concentrations in most surface waters and therefore are not affected greatly by inputs from volcanic ashfall, and are also of low concern in drinking water, with the possible exception of fluorine. The elements iron, manganese and aluminium are commonly enriched over background levels by volcanic ashfall. These elements may impart a metallic taste to water, and may produce red, brown or black staining of whiteware, but are not considered a health risk. Volcanic ashfalls are not known to have caused problems in water supplies for toxic trace elements such as mercury (Hg) and lead (Pb) which occur at very low levels in ash leachates.

A further point to note is that drinking-water treatment commonly involves the addition of treatment chemicals such as aluminium sulfate or ferric chloride as flocculants, lime for pH adjustment, chlorine for disinfection and fluoride compounds for dental health.

The physical impacts of ashfall can affect the operation of water treatment plants. Ash can block intake structures, cause severe abrasion damage to pump impellers and overload pump motors. Many water treatment plants have an initial coagulation/flocculation step that is automatically adjusted to turbidity (the level of suspended solids, measured in nephelometric turbidity units) in the incoming water. In most cases, changes in turbidity caused by suspended ash particles will be within the normal operating range of the plant and can be managed satisfactorily by adjusting the addition of coagulant. Ashfalls will be more likely to cause problems for plants that are not designed for high levels of turbidity and which may omit coagulation/flocculation treatment. Ash can enter filtration systems such as open sand filters both by direct fallout and via intake waters. In most cases, increased maintenance will be required to manage the effects of an ashfall, but there will not be service interruptions.

The final step of drinking water treatment is disinfection to ensure that final drinking water is free from infectious microorganisms. As suspended particles (turbidity) can provide a growth substrate for microorganisms and can protect them from disinfection treatment, it is extremely important that the water treatment process achieves a good level of removal of suspended particles.

Many small communities obtain their drinking water from diverse sources (lakes, streams, springs and groundwater wells). Levels of treatment vary widely, from rudimentary systems with coarse screening or settling followed by disinfection (usually chlorination), to more sophisticated systems using a filtration step. Unless a high quality source is used, such as secure groundwater, disinfection alone is unlikely to guarantee that drinking water is safe from protozoa such as Giardia and Cryptosporidium, which are relatively resistant to standard disinfectants and which require additional removal steps such as filtration.

Volcanic ashfall is likely to have major effects on these systems. Ash will clog intake structures, cause abrasion damage to pumps and block pipes, settling ponds and open filters. High levels of turbidity are very likely to interfere with disinfection treatment and doses may have to be adjusted to compensate. It is essential to monitor chlorine residuals in the distribution system.

Many households, and some small communities, rely on rainwater for their drinking water supplies. Roof-fed systems are highly vulnerable to contamination by ashfall, as they have a large surface area relative to the storage tank volume. In these cases, leaching of chemical contaminants from the ashfall can become a health risk and drinking of water is not recommended. Prior to an ashfall, downpipes should be disconnected so that water in the tank is protected. A further problem is that the surface coating of fresh volcanic ash can be acidic. Unlike most surface waters, rainwater generally has a very low alkalinity (acid-neutralising capacity) and thus ashfall may acidify tank waters. This may lead to problems with plumbosolvency, whereby the water is more aggressive towards materials that it comes into contact with. This can be a particular problem if there are lead-head nails or lead flashing used on the roof, and for copper pipes and other metallic plumbing fittings.

During ashfall events large demands are commonly placed on water resources for cleanup and shortages can result. Shortages compromise key services such as firefighting and can lead to a lack of water for hygiene, sanitation and drinking. Municipal authorities need to monitor and manage this water demand carefully, and may need to advise the public to utilise cleanup methods that do not use water (e.g., cleaning with brooms rather than hoses).

Wastewater treatment

Wastewater networks may sustain damage similar to water supply networks. It is very difficult to exclude ash from the sewerage system. Systems with combined storm water/sewer lines are most at risk. Ash will enter sewer lines where there is inflow/infiltration by stormwater through illegal connections (e.g., from roof downpipes), cross connections, around manhole covers or through holes and cracks in sewer pipes.

Ash-laden sewage entering a treatment plant is likely to cause failure of mechanical prescreening equipment such as step screens or rotating screens. Ash that penetrates further into the system will settle and reduce the capacity of biological reactors as well as increasing the volume of sludge and changing its composition.

Aircraft

The principal damage sustained by aircraft flying into a volcanic ash cloud is abrasion to forward-facing surfaces, such as the windshield and leading edges of the wings, and accumulation of ash into surface openings, including engines. Abrasion of windshields and landing lights will reduce visibility forcing pilots to rely on their instruments. However, some instruments may provide incorrect readings as sensors (e.g., pitot tubes) can become blocked with ash. Ingestion of ash into engines causes abrasion damage to compressor fan blades. The ash erodes sharp blades in the compressor, reducing its efficiency. The ash melts in the combustion chamber to form molten glass. The ash then solidifies on turbine blades, blocking air flow and causing the engine to stall.

The composition of most ash is such that its melting temperature is within the operating temperature (>1000 °C) of modern large jet engines.[37] The degree of impact depends upon the concentration of ash in the plume, the length of time the aircraft spends within the plume and the actions taken by the pilots. Critically, melting of ash, particularly volcanic glass, can result in accumulation of resolidified ash on turbine nozzle guide vanes, resulting in compressor stall and complete loss of engine thrust.[38] The standard procedure of the engine control system when it detects a possible stall is to increase power which would exacerbate the problem. It is recommended that pilots reduce engine power and quickly exit the cloud by performing a descending 180° turn.[38] Volcanic gases, which are present within ash clouds, can also cause damage to engines and acrylic windshields, although this damage may not surface for many years.

There are many instances of damage to jet aircraft as a result of an ash encounter. On 24 June 1982 a British Airways Boeing 747-236B (Flight 9) flew through the ash cloud from the eruption of Mount Galunggung, Indonesia resulting in the failure of all four engines. The plane descended 24,000 feet (7,300 m) in 16 minutes before the engines restarted, allowing the aircraft to make an emergency landing. On 15 December 1989 a KLM Boeing 747-400 (Flight 867) also lost power to all four engines after flying into an ash cloud from Mount Redoubt, Alaska. After dropping 14,700 feet (4,500 m) in four minutes, the engines were started just 1–2 minutes before impact. Total damage was US$80 million and it took 3 months' work to repair the plane.[37] In the 1990s a further US$100 million of damage was sustained by commercial aircraft (some in the air, others on the ground) as a consequence of the 1991 eruption of Mount Pinatubo in the Philippines.[37]

In April 2010 airspace all over Europe was affected, with many flights cancelled-which was unprecedented-due to the presence of volcanic ash in the upper atmosphere from the eruption of the Icelandic volcano Eyjafjallajökull.[39] On 15 April 2010 the Finnish Air Force halted training flights when damage was found from volcanic dust ingestion by the engines of one of its Boeing F-18 Hornet fighters.[40] On 22 April 2010 UK RAF Typhoon training flights were also temporarily suspended after deposits of volcanic ash were found in a jet's engines.[41] In June 2011 there were similar closures of airspace in Chile, Argentina, Brazil, Australia and New Zealand, following the eruption of Puyehue-Cordón Caulle, Chile.

VAAC Coverage
Coverage of the nine VAAC around the world
AIRBUS-AVOID
The AVOID instrument mounted on the fuselage of an AIRBUS A340 test aircraft.

Volcanic ash clouds are very difficult to detect from aircraft as no onboard cockpit instruments exist to detect them. However, a new system called Airborne Volcanic Object Infrared Detector (AVOID) has recently been developed by Dr Fred Prata[42] while working at CSIRO Australia[43] and the Norwegian Institute for Air Research, which will allow pilots to detect ash plumes up to 60 km (37 mi) ahead and fly safely around them.[44] The system uses two fast-sampling infrared cameras, mounted on a forward-facing surface, that are tuned to detect volcanic ash. This system can detect ash concentrations of <1 mg/m3 to > 50 mg/m3, giving pilots approximately 7–10 minutes warning.[44] The camera was tested[45][46] by the easyJet airline company,[47] AIRBUS and Nicarnica Aviation (co-founded by Dr Fred Prata). The results showed the system could work to distances of ~60 km and up to 10,000 ft [48] but not any higher without some significant modifications.

In addition, ground and satellite based imagery, radar, and lidar can be used to detect ash clouds. This information is passed between meteorological agencies, volcanic observatories and airline companies through Volcanic Ash Advisory Centers (VAAC). There is one VAAC for each of the nine regions of the world. VAACs can issue advisories describing the current and future extent of the ash cloud.

Volcanic ash not only affects in-flight operations but can affect ground-based airport operations as well. Small accumulations of ash can reduce visibility, create slippery runways and taxiways, infiltrate communication and electrical systems, interrupt ground services, damage buildings and parked aircraft.[49] Ash accumulation of more than a few millimeters requires removal before airports can resume full operations. Ash does not disappear (unlike snowfalls) and must be disposed of in a manner that prevents it from being remobilised by wind and aircraft.

Land transport

Ash may disrupt transportation systems over large areas for hours to days, including roads and vehicles, railways and ports and shipping. Falling ash will reduce the visibility which can make driving difficult and dangerous.[23] In addition, fast travelling cars will stir up ash, creating billowing clouds which perpetuate ongoing visibility hazards. Ash accumulations will decrease traction, especially when wet, and cover road markings.[23] Fine-grained ash can infiltrate openings in cars and abrade most surfaces, especially between moving parts. Air and oil filters will become blocked requiring frequent replacement. Rail transport is less vulnerable, with disruptions mainly caused by reduction in visibility.[23]

Marine transport can also be impacted by volcanic ash. Ash fall will block air and oil filters and abrade any moving parts if ingested into engines. Navigation will be impacted by a reduction in visibility during ash fall. Vesiculated ash (pumice and scoria) will float on the water surface in ‘pumice rafts’ which can clog water intakes quickly, leading to over heating of machinery.[23]

Communications

Telecommunication and broadcast networks can be affected by volcanic ash in the following ways: attenuation and reduction of signal strength; damage to equipment; and overloading of network through user demand. Signal attenuation due to volcanic ash is not well documented; however, there have been reports of disrupted communications following the 1969 Surtsey eruption and 1991 Mount Pinatubo eruption. Research by the New Zealand-based Auckland Engineering Lifelines Group determined theoretically that impacts on telecommunications signals from ash would be limited to low frequency services such as satellite communication.[34] Signal interference may also be caused by lightning, as this is frequently generated within volcanic eruption plumes.[50]

Telecommunication equipment may become damaged due to direct ash fall. Most modern equipment requires constant cooling from air conditioning units. These are susceptible to blockage by ash which reduces their cooling efficiency.[51] Heavy ash falls may cause telecommunication lines, masts, cables, aerials, antennae dishes and towers to collapse due to ash loading. Moist ash may also cause accelerated corrosion of metal components.[34]

Reports from recent eruptions suggest that the largest disruption to communication networks is overloading due to high user demand.[23] This is common of many natural disasters.

Computers

Computers may be impacted by volcanic ash, with their functionality and usability decreasing during ashfall, but it is unlikely they will completely fail.[52] The most vulnerable components are the mechanical components, such as cooling fans, cd drives, keyboard, mice and touch pads. These components can become jammed with fine grained ash causing them to cease working; however, most can be restored to working order by cleaning with compressed air. Moist ash may cause electrical short circuits within desktop computers; however, will not affect laptop computers.[52]

Buildings and structures

Damage to buildings and structures can range from complete or partial roof collapse to less catastrophic damage of exterior and internal materials. Impacts depend on the thickness of ash, whether it is wet or dry, the roof and building design and how much ash gets inside a building. The specific weight of ash can vary significantly and rain can increase this by 50–100%.[8] Problems associated with ash loading are similar to that of snow; however, ash is more severe as 1) the load from ash is generally much greater, 2) ash does not melt and 3) ash can clog and damage gutters, especially after rain fall. Impacts for ash loading depend on building design and construction, including roof slope, construction materials, roof span and support system, and age and maintenance of the building.[8] Generally flat roofs are more susceptible to damage and collapse than steeply pitched roofs. Roofs made of smooth materials (sheet metal or glass) are more likely to shed ash than roofs made with rough materials (thatch, asphalt or wood shingles). Roof collapse can lead to widespread injuries and deaths and property damage. For example, the collapse of roofs from ash during the 15 June 1991 Mount Pinatubo eruption killed about 300 people.[53]

Human and animal health

Ash particles of less than 10 µm diameter suspended in the air are known to be inhalable, and people exposed to ash falls have experienced respiratory discomfort, breathing difficulty, eye and skin irritation, and nose and throat symptoms.[54] Most of these effects are short-term and are not considered to pose a significant health risk to those without pre-existing respiratory conditions.[55] The health effects of volcanic ash depend on the grain size, mineralogical composition and chemical coatings on the surface of the ash particles.[55] Additional factors related to potential respiratory symptoms are the frequency and duration of exposure, the concentration of ash in the air and the respirable ash fraction; the proportion of ash with less than 10 µm diameter, known as PM10. The social context may also be important.

Chronic health effects from volcanic ash fall are possible, as exposure to free crystalline silica is known to cause silicosis. Minerals associated with this include quartz, cristobalite and tridymite, which may all be present in volcanic ash. These minerals are described as ‘free’ silica as the SiO2 is not attached to another element to create a new mineral. However, magmas containing less than 58% SiO2 are thought to be unlikely to contain crystalline silica.[55]

The exposure levels to free crystalline silica in the ash are commonly used to characterise the risk of silicosis in occupational studies (for people who work in mining, construction and other industries,) because it is classified as a human carcinogen by the International Agency for Research on Cancer. Guideline values have been created for exposure, but with unclear rationale; UK guidelines for particulates in air (PM10) are 50 µg/m3 and USA guidelines for exposure to crystalline silica are 50 µg/m3.[55] It is thought that the guidelines on exposure levels could be exceeded for short periods of time without significant health effects on the general population.[54]

There have been no documented cases of silicosis developed from exposure to volcanic ash. However, long-term studies necessary to evaluate these effects are lacking.[55]

Ingesting ash

Ingesting ash may be harmful to livestock, causing abrasion of the teeth, and in cases of high fluorine content, fluorine poisoning (toxic at levels of >100 µg/g) for grazing animals.[56] It is known from the 1783 eruption of Laki in Iceland that fluorine poisoning occurred in humans and livestock as a result of the chemistry of the ash and gas, which contained high levels of Hydrogen Fluoride. Following the 1995/96 Mount Ruapehu eruptions in New Zealand, two thousand ewes and lambs died after being affected by fluorosis while grazing on land with only 1–3 mm of ash fall.[56] Symptoms of flourorsis among cattle exposed to ash Brown-yellow to green-black mottles in the teeth, and hypersensibility to pressure in the legs and back.[57] Ash ingestion may also cause gastrointestinal blockages.[34] Sheep that ingested ash from the 1991 Mount Hudson volcanic eruption in Chile, suffered from diarrhoea and weakness.

Other effects on livestock

Ash accumulating in the back wool of sheep may add significant weight, leading to fatigue and sheep that can not stand up. Rainfall may result in a significant burden as it adds weight to ash.[58] Pieces of wool may fall away and any remaining wool on sheep may be worthless as poor nutrition associated to volcanic eruptions impacts on que quality of the fibre.[58] As the usual pastures and plants become covered in volcanic ash during eruption some livestock may resort to eat whatever is available including toxic plants.[59] There are reports of goats and sheep in Chile and Argentina having natural aborts in connection to volcanic eruptions.[60]

Environment and agriculture

Volcanic ash can have a detrimental impact on the environment which can be difficult to predict due to the large variety of environmental conditions that exist within the ash fall zone. Natural waterways can be impacted in the same way as urban water supply networks. Ash will increase water turbidity which can reduce the amount of light reaching lower depths, which can inhibit growth of submerged aquatic plants and consequently affect species which are dependent on them such as fish and shellfish. High turbidity can also affect the ability of fish gills to absorb dissolved oxygen. Acidification will also occur, which will reduce the pH of the water and impact the fauna and flora living in the environment. Fluoride contamination will occur if the ash contains high concentrations of fluoride.

Ash accumulation will also affect pasture, plants and trees which are part of the horticulture and agriculture industries. Thin ash falls (<20 mm) may put livestock off eating, and can inhibit transpiration and photosynthesis and alter growth. There may be an increase in pasture production due to a mulching effect and slight fertilizing effect, such as occurred following the 1980 Mount St. Helens and 1995/96 Mt Ruapehu eruptions.[61][62] Heavier falls will completely bury pastures and soil leading to death of pasture and sterilization of the soil due to oxygen deprivation. Plant survival is dependent on ash thickness, ash chemistry, compaction of ash, amount of rainfall, duration of burial and the length of plant stalks at the time of ash fall.[8] The acidic nature of ash will lead to elevated soil sulfur levels and lowered soil pH, which can reduce the availability of essential minerals and alter the soil's characteristics so that crops and plants will not survive. Ash will also impact upon arable crops, such as fruit, vegetables and grain. Ash can burn plant and crop tissue reducing quality, contaminate crops during harvest and damage plants from ash loading.

Young forests (trees <2 years old) are most at risk from ash falls and are likely to be destroyed by ash deposits >100 mm.[63] Ash fall is unlikely to kill mature trees, but ash loading may break large branches during heavy ash falls (>500 mm). Defoliation of trees may also occur, especially if there is a coarse ash component within the ash fall.[8]

Land rehabilitation after ash fall may be possible depending on the ash deposit thickness. Rehabilitation treatment may include: direct seeding of deposit; mixing of deposit with buried soil; scraping of ash deposit from land surface; and application of new topsoil over the ash deposit.[34]

Interdependence

Interdependency of volcanic ashfall impacts
Interdependency of volcanic ashfall impacts from the Eyjafjallajökull 2010 eruptions.

Critical infrastructure and infrastructure services are vital to the functionality of modern society, to provide: medical care, policing, emergency services, and lifelines such as water, wastewater, and power and transportation links. Often critical facilities themselves are dependent on such lifelines for operability, which makes them vulnerable to both direct impacts from a hazard event and indirect effects from lifeline disruption.[64]

The impacts on lifelines may also be inter-dependent. The vulnerability of each lifeline may depend on: the type of hazard, the spatial density of its critical linkages, the dependency on critical linkages, susceptibility to damage and speed of service restoration, state of repair or age, and institutional characteristics or ownership.[28]

The 2010 eruption of Eyjafjallajokull in Iceland highlighted the impacts of volcanic ash fall in modern society and our dependence on the functionality of infrastructure services. During this event the airline industry suffered business interruption losses of €1.5–2.5 billion from the closure of European airspace for six days in April 2010 and subsequent closures into May 2010.[65] Ash fall from this event is also known to have caused local crop losses in agricultural industries, losses in the tourism industry, destruction of roads and bridges in Iceland (in combination with glacial melt water), and costs associated with emergency response and clean-up. However, across Europe there were further losses associated with travel disruption, the insurance industry, the postal service, and imports and exports across Europe and worldwide. These consequences demonstrate the interdependency and diversity of impacts from a single event.[35]

Preparedness, mitigation and management

Two management methods during the 2014 eruptions of Kelud: sweeping (top) and spraying with water (bottom)

Ash in Yogyakarta during the 2014 eruption of Kelud 01
Ash in Yogyakarta during the 2014 eruption of Kelud 17

Preparedness for ashfalls should involve sealing buildings, protecting infrastructure and homes, and storing sufficient supplies of food and water to last until the ash fall is over and clean-up can begin. Dust masks can be worn to reduce inhalation of ash and mitigate against any respiratory health affects.[54] Goggles can be worn to protect against eye irritation.

The International Volcanic Ashfall Impacts Working Group of IAVCEI maintains a regularly updated database of impacts and mitigations strategies.

At home, staying informed about volcanic activity, and having contingency plans in place for alternative shelter locations, constitutes good preparedness for an ash fall event. This can prevent some impacts associated with ash fall, reduce the effects, and increase the human capacity to cope with such events. A few items such as a flashlight, plastic sheeting to protect electronic equipment from ash ingress, and battery operated radios, are extremely useful during ash fall events.[8]

The protection of infrastructure must also be considered within emergency preparedness. Critical facilities that need to remain operable should be identified, and all others should be shut down to reduce damage. It is also important to keep ash out of buildings, machinery and lifeline networks (in particular water and wastewater systems,) to prevent some of the damage caused by ash particles. Windows and doors should be closed and shuttered if possible, to prevent ingress of ash into buildings.

Communication plans should be made beforehand to inform of mitigation actions being undertaken. Spare parts and back-up systems should be in place prior to ash fall events to reduce service disruption and return functionality as quickly as possible. Good preparedness also includes the identification of ash disposal sites, before ash fall occurs, to avoid further movement of ash and to aid clean-up.[66] Protective equipment such as eye protection and dust masks should be deployed for clean-up teams in advance of ash fall events.

Some effective techniques for the management of ash have been developed including cleaning methods and cleaning apparatus, and actions to mitigate or limit damage. The latter include covering of openings such as: air and water intakes, aircraft engines and windows during ash fall events. Roads may be closed to allow clean-up of ash falls, or speed restrictions may be put in place, in order to prevent motorists from developing motor problems and becoming stranded following an ash fall.[67] To prevent further effects on underground water systems or waste water networks, drains and culverts should be unblocked and ash prevented from entering the system.[66] Ash can be moistened (but not saturated) by sprinkling with water, to prevent remobilisation of ash and to aid clean-up.[67] Prioritisation of clean-up operations for critical facilities and coordination of clean-up efforts also constitute good management practice.[66][67][68]

It is recommended to evacuate livestock in areas where ashfall may reach 5 cm or more.[69]

Volcanic ash soils

Volcanic ash's primary use is that of a soil enricher. Once the minerals in ash are washed into the soil by rain or other natural processes, it mixes with the soil to create an andisol layer. This layer is highly rich in nutrients and is very good for agricultural use; the presence of lush forests on volcanic islands is often as a result of trees growing and flourishing in the phosphorus and nitrogen-rich andisol.[70] Volcanic ash can also be used as a replacement for sand.[71]

See also

References

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External links

2010 eruptions of Mount Merapi

In late October 2010, Mount Merapi in Central Java, Indonesia began an increasingly violent series of eruptions that continued into November. Seismic activity around the volcano increased from mid-September onwards, culminating in repeated outbursts of lava and ashes. Large eruption columns formed, causing numerous pyroclastic flows down the heavily populated slopes of the volcano. Merapi's eruption was said by authorities to be the largest since the 1870s.

Over 350,000 people were evacuated from the affected area. However, many remained behind or returned to their homes while the eruptions were continuing. 353 people were killed during the eruptions, many as a result of pyroclastic flows. The ash plumes from the volcano also caused major disruption to aviation across Java.

The mountain continued to erupt until 30 November 2010. On 3 December 2010 the official alert status was reduced to level 3, from level 4, as the eruptive activity had subsided.

Air travel disruption after the 2010 Eyjafjallajökull eruption

In response to concerns that volcanic ash ejected during the 2010 eruptions of Eyjafjallajökull in Iceland would damage aircraft engines, the controlled airspace of many European countries was closed to instrument flight rules traffic, resulting in the largest air-traffic shut-down since World War II. The closures caused millions of passengers to be stranded not only in Europe, but across the world. With large parts of European airspace closed to air traffic, many more countries were affected as flights to, from, and over Europe were cancelled.

After an initial uninterrupted shutdown over much of northern Europe from 15 to 23 April, airspace was closed intermittently in different parts of Europe in the following weeks, as the path of the ash cloud was tracked. The ash cloud caused further disruptions to air travel operations in Ireland, Northern Ireland, and Scotland on 4 and 5 May and in Spain, Portugal, northern Italy, Austria, and southern Germany on 9 May. Irish and UK airspace closed again on 16 May and reopened on 17 May.The eruption occurred beneath glacial ice. The cold water from the melting ice chilled the lava quickly, causing it to fragment into very small particles of glass (silica) and ash, which were carried into the eruption plume. The extremely fine ash particles and the large volume of steam from the glacial meltwater sent an ash plume hazardous to aircraft rapidly high into the upper atmosphere. The presence and location of the plume depended upon the state of the eruption and the winds. The large amount of glacial meltwater flowing into the eruption vent made this eruption so explosive that it ejected its ash plume directly into the jet stream, which was unusually stable and south-easterly. The ash was then carried over Europe into some of the busiest airspace in the world.

The International Air Transport Association (IATA) estimated that the airline industry worldwide would lose €148 million (US$200 million, GB£130 million) a day during the disruption. IATA stated that the total loss for the airline industry was around US$1.7 billion (£1.1 billion, €1.3 billion). The Airport Operators Association (AOA) estimated that airports lost £80 million over the six-and-a-half days. Over 95,000 flights had been cancelled all across Europe during the six-day travel ban, with later figures suggesting 107,000 flights cancelled during an 8-day period, accounting for 48% of total air traffic and roughly 10 million passengers.

Assyrtiko

Assyrtiko or Asyrtiko is a white Greek wine grape indigenous to the island of Santorini. Assyrtiko is widely planted in the arid volcanic-ash-rich soil of Santorini and other Aegean islands, such as Paros. It is also found on other scattered regions of Greece such as Chalkidiki.On Santorini, many old vine plantations (over 70 years of age) of Assyrtiko exist, of which many are non-grafted. These plantations have shown resistance to Phylloxera. As the only European grape vine known to be resistant to wine blight, there is speculation that the actual source of this resistance may arise from the volcanic ash in which the vines grow, and not from the vine itself.

Eruption column

An eruption column is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a column that may rise many kilometers into the air above the vent of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km (25 mi), penetrating the stratosphere. Stratospheric injection of aerosols by volcanoes is a major cause of short-term climate change.

A common occurrence in explosive eruptions is column collapse when the eruption column is or becomes too dense to be lifted high into the sky by air convection, and instead falls down the slopes of the volcano to form pyroclastic flows or surges (although the latter is less dense). On some occasions, if the material isn't dense enough to fall, it may create pyrocumulonimbus clouds.

Explosive eruption

In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. Explosive eruptions can send rocks, dust, gas and pyroclastic material up to 20 km (12 mi) into the atmosphere at a rate of up to 100,000 tonnes per second, traveling at several hundred meters per second. This cloud may then collapse, creating a fast-moving pyroclastic flow of hot volcanic matter.

Eyjafjallajökull

Eyjafjallajökull (Icelandic: [ˈeiːjaˌfjatl̥aˌjœːkʏtl̥] (listen) EY-ya-FYA-htla-YUH-kuhtl; English: Island Mountain Glacier) is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano with a summit elevation of 1,651 metres (5,417 ft). The volcano has erupted relatively frequently since the last glacial period, most recently in 2010.

Imogolite

Imogolite is an aluminium silicate clay mineral with the chemical formula Al2SiO3(OH)4. It occurs in soils formed from volcanic ash and was first described in 1962 for an occurrence in Uemura, Kumamoto prefecture, Kyushu Region, Japan. Its name originates from the Japanese word imogo, which refers to the brownish yellow soil derived from volcanic ash. It occurs together with allophane, quartz, cristobalite, gibbsite, vermiculite and limonite.Imogolite consists of a network of nanotubes with an outer diameter of ca. 2 nm and an inner diameter of ca. 1 nm. The tube walls are formed by continuous Al(OH)3 (gibbsite) sheets and orthosilicate anions (O3SiOH groups). Owing to its tubular structure, natural availability, and low toxicity, imogolite has potential applications in polymer composites, fuel gas storage, absorbents, and as a catalyst support in chemical catalysis.

Kaʻū Desert

The Kaʻū Desert is a leeward desert in the district of Kaʻū, the southernmost district on the Big Island of Hawaii, and is made up mostly of dried lava remnants, volcanic ash, sand and gravel. The desert covers an area of the Kīlauea Volcano along the Southwest rift zone. The area lacks any vegetation, mainly due to acid rainfall.

Lapilli

Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli (singular: lapillus) is Latin for "little stones".

By definition lapilli range from 2 to 64 mm (0.08 to 2.52 in) in diameter. A pyroclastic particle greater than 64 mm in diameter is known as a volcanic bomb when molten, or a volcanic block when solid. Pyroclastic material with particles less than 2 mm in diameter is referred to as volcanic ash.

Melas Chasma

Melas Chasma is a canyon on Mars, the widest segment of the Valles Marineris canyon system, located east of Ius Chasma at 9.8°S, 283.6°E in Coprates quadrangle. It cuts through layered deposits that are thought to be sediments from an old lake that resulted from runoff of the valley networks to the west. Other theories include windblown sediment deposits and volcanic ash. Support for abundant, past water in Melas Chasma is the discovery by MRO of hydrated sulfates. In addition, sulfate and iron oxides were found by the same satellite. Although not chosen as one of the finalists, it was one of eight potential landing sites for the Mars 2020 rover, a mission with a focus on astrobiology.

The floor of Melas Chasma is about 70% younger massive material that is thought to be volcanic ash whipped up by the wind into eolian features. It also contains rough floor material from the erosion of the canyon walls. Around the edges of Melas is also a lot of slide material. This is also the deepest part of the Valles Marineris system at eleven kilometers deep from the surrounding surface, from here to the outflow channels are about a 0.03 degree slope upward to the northern plains, which means that filling the canyon with fluid would give a lake with a depth of about one kilometer before the fluid would flow out onto the northern plains.In a recent study of southwestern Melas Chasma using high-resolution image, topographic and spectral datasets eleven fan-shaped landforms were found. These fans add to growing evidence that Melas Chasma once held a lake that had fluctuating levels.Using HiRISE images, CTX images, and DEM's, a team of researchers mapped many channels and inverted channels in Melas Chasma. A digital elevation model (DEM) is a digital model or 3D representation of a terrain's surface. In addition, they found dendritic networks of channels in the plateaus just above the Chasma. Channels appeared to have formed at different times, hence there were "wet-dry" phases in the history of Melas Chasma. The whole region may have had liquid water for extended periods in the early Hesperian.The canyon's depth suggests that this location may be the best site for a manned outpost as it would have the highest natural air pressure on Mars. Equatorial solar irradiation and access to water would enhance this option still further.

Mount Job

Mount Job is one of six named volcanic peaks of the Mount Meager massif in British Columbia, Canada. It is a pile of rubble held together by volcanic ash and sand. The main summit of Mount Job is hard to climb because of difficult access and its horribly loose rock.

Pozzolana

Pozzolana, also known as pozzolanic ash (pulvis puteolanus in Latin), is a natural siliceous or siliceous and aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reaction). In this reaction insoluble calcium silicate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties. The designation pozzolana is derived from one of the primary deposits of volcanic ash used by the Romans in Italy, at Pozzuoli. Nowadays the definition of pozzolana encompasses any volcanic material (pumice or volcanic ash), predominantly composed of fine volcanic glass, that is used as a pozzolan. Note the difference with the term pozzolan, which exerts no bearing on the specific origin of the material, as opposed to pozzolana, which can only be used for pozzolans of volcanic origin, primarily composed of volcanic glass.

Pyroclastic rock

Pyroclastic rocks or pyroclastics (derived from the Greek: πῦρ, meaning fire; and κλαστός, meaning broken) are sedimentary clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic. Commonly associated with unsieved volcanic activity—such as Plinian or krakatoan eruption styles, or phreatomagmatic eruptions—pyroclastic deposits are commonly formed from airborne ash, lapilli and bombs or blocks ejected from the volcano itself, mixed in with shattered country rock.

Pyroclastic rocks may be a range of clast sizes, from the largest agglomerates, to very fine ashes and tuffs. Pyroclasts of different sizes are classified as volcanic bombs, lapilli, and volcanic ash. Ash is considered to be pyroclastic because it is a fine dust made up of volcanic rock. One of the most spectacular forms of pyroclastic deposit are the ignimbrites, deposits formed by the high-temperature gas-and-ash mix of a pyroclastic flow event.

Qadad

Qadad (Arabic: قضاض‎, qadâd, kʉðað) or qudad is a waterproof plaster surface, made of a lime plaster treated with slaked lime and oils and fats. The technique is well over a millennium old and can be used as a roof covering.Volcanic ash, pumice or other crushed volcanic aggregate are often used as pozzolanic agents.

Due to the slowness of some of the chemical reactions, qadad mortar can take over a hundred days to prepare, from quarrying of raw materials to the beginning of application to the building. It can also take over a year to set fully.In 2004, a documentary film Qudad, Re-inventing a Tradition was made by the filmmaker Caterina Borelli. It documents the restoration of the Amiriya Complex, which was awarded the Aga Khan Award for Architecture in 2007.

Reventador

Reventador is an active stratovolcano which lies in the eastern Andes of Ecuador. It lies in a remote area of the national park of the same name, which is Spanish for 'exploder' or 'ripper'. Since 1541 it has erupted over 25 times, although its isolated location means that many of its eruptions have gone unreported. Its most recent eruption began in 2008 and is ongoing as of July 4, 2017. The largest historical eruption occurred in 2002. During that eruption the plume from the volcano reached a height of 17 km and pyroclastic flows went up to 7 km from the cone.

On March 30, 2007, the mountain ejected ash again. The ash reached a height of about two miles (3 km, 11,000 ft). No injuries or damages have been reported.[1]

The volcano's main peak lies inside a U-shaped caldera which is open towards the Amazon basin to the east. Its lavas are andesitic.

According to NOAA Aviation Weather, a Volcanic Ash Advisory was issued at 2017-10-18T 13:17:00Z for volcanic ash to 13,000 ft.

SIGMET

SIGMET, or Significant Meteorological Information AIM 7-1-6 , is a weather advisory that contains meteorological information concerning the safety of all aircraft. There are two types of SIGMETs: convective and non-convective.

The criteria for a non-convective SIGMET to be issued are severe or greater turbulence over a 3,000-square-mile (7,800 km2) area, severe or greater icing over a 3,000-square-mile (7,800 km2) area or IMC over a 3,000-square-mile (7,800 km2) area due to dust, sand, or volcanic ash.

This information is usually broadcast on the ATIS at ATC facilities, as well as over VOLMET stations. They are assigned an alphabetic designator from N through Y (excluding S and T). SIGMETs are issued as needed, and are valid up to four hours. SIGMETS for hurricanes and volcanic ash outside the CONUS are valid up to six hours.A Convective SIGMET is issued for convection over the Continental U.S. Convective SIGMETs are issued for an area of embedded thunderstorms, a line of thunderstorms, thunderstorms greater than or equal to VIP level 4 affecting 40% or more of an area at least 3000 square miles, and severe surface weather including surface winds greater than or equal to 50 knots, hail at the surface greater than or equal to 3/4 inches in diameter, and tornadoes. Severe thunderstorms are characterized by tornado(s), hail 3/4 inches or greater, or wind gusts 50 knots or greater. A Convective SIGMET is valid for 2 hours and they are issued hourly at Hour+55.

Tuff

Tuff (from the Italian tufo), also known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa", particularly when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous.

Tuff is a relatively soft rock, so it has been used for construction since ancient times. Since it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the moai statues in Easter Island.

Tuff can be classified as either sedimentary or igneous rock. They are usually studied in the context of igneous petrology, although they are sometimes described using sedimentological terms.

Volcanic Ash Advisory Center

A Volcanic Ash Advisory Center (VAAC) is a group of experts responsible for coordinating and disseminating information on atmospheric volcanic ash clouds that may endanger aviation. As at 2019, there are nine Volcanic Ash Advisory Centers located around the world, each one focusing on a particular geographical region. Their analyses are made public in the form of Volcanic Ash Advisories (VAA), involving expertise analysis of satellite observations, ground and pilot observations and interpretation of ash dispersion models. The worldwide network of Volcanic Ash Advisory Centers was set up by the International Civil Aviation Organization (ICAO), an agency of the United Nations, as part of the International Airways Volcano Watch (IAVW), an international set of arrangements for monitoring and providing warnings to aircraft of volcanic ash. The operations and development of the IAVW are coordinated by the Meteorology Panel (METP) established by the ICAO Air Navigation Commission. The individual VAACs are run as part of national weather forecasting organisations of the country where they are based, e.g. the US NOAA or the British Met Office.

Wheeler Geologic Area

The Wheeler Geologic Area is a highly eroded outcropping of layers of volcanic ash, in the La Garita Mountains of Mineral County, in southern Colorado in the western United States about 10 miles east north-east of Creede. The ash is the result of eruptions from the La Garita Caldera approximately 25 millions years ago.

The area was designated a National Monument from 1908 until 1950 and was Colorado's first National Monument. It is now part of the La Garita Wilderness and administered by the Rio Grande National Forest. Lying just below the crest of the range at an elevation of 11,960 feet (3645 m), it can be reached by an 8.4-mile hike on the East Bellows Trail (FS790), or by a difficult 14 mile four-wheel drive road.

The formations are named after Captain George M. Wheeler, who explored and surveyed this area in 1874 for the U.S. Army.

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