Volcanic ash is a mixture of unconsolidated particles or pieces of rocks, mineral crystals, and glass shards measuring less than 2 mm in size ejected during a volcanic eruption.
It forms part of the tephra or pyroclasts suspended by hot gases released during an eruption that form the eruption plume or column.
Tephra or pyroclasts collectively refer to debris ejected during eruptions. These particles are volcanic ash, lapilli, volcanic bombs, and blocks. Some authors incorrectly refer to tephra as volcanic ash.
On the other hand, an eruption plume or column is a superheated cloud of gas and tephra ejected from a volcanic vent or rootless crater during an explosive eruption.
While it uses the name ash, don’t mistake volcanic ash to be the same as the ash you get when you burn matter like grass, wood, leaves, or paper. No. It doesn’t form from combustion.
Lastly, volcanic ash refers to the size of fragments ejected during volcanism. It doesn’t refer to specific compositions or physical or chemical properties.
Physical and chemical properties
Volcanic ash’s physical, mineral composition, and chemical properties depend on eruption style. These styles range from effusive with low energy to explosive with high energy.
On the other hand, the eruption style depends on magma type, temperature, crystal content, and dissolved gas content.
Low-energy eruptions involve dark-colored, low-viscosity mafic magmas like basaltic or basanite. These magmas erupt at high temperatures and have less volatiles. Also, they are low in silica, i.e., 45-52% SiO2, but higher in magnesium and iron.
The other end has high-energy explosions from light-colored, highly viscous viscosity felsic magma like dacite and rhyolite.
Such magmas are high in silica > 65% SiO2. Also, they have considerable sodium and potassium. However, they are low in iron and magnesium.
Between these extreme ends are intermediate magmas whose eruption energy, viscosity, and composition lie between mafic and felsic magmas. Examples are andesite and latite.
1. Volcanic ash composition
Volcanic ash’s chemical and mineral composition depends on magma type. It can be mafic/basic, intermediate, or felsic/acidic. Ultramafic rarely produces this ash.
Typical volcanic ash’s chemical composition is variable amounts of SiO2, Al2O3, CaO, Fe2O3, FeO, MgO, K2O, and Na2O. Also, they can have smaller amounts of P2O5, TiO2, etc.
Silica is the most abundant, accounting for 45-52% in mafic, 52-63% in intermediate, and more than 63 to nearly 80 in felsic magmas.
Mineralogically, volcanic ash mainly consists of glass shards. These are natural volcanic glass formed from rapid quenching that prevents mineral formation.
However, it may have minute crystals called microlites or minerals that formed before the eruption, i.e., phenocrysts. Also, it may have foreign minerals plucked from country rock or xenocrysts and accidental clasts.
The composition of accidental clasts and xenocrysts will vary. It depends on the country rock they came from.
On the other hand, phenocrysts and microlites depend on magma composition.
For instance, felsic will have phenocrysts like quartz, oligoclase, and k-feldspar and less common amphibole, biotite, or pyroxene.
On the other hand, intermediate magmas will have plagioclase, sometimes hornblende or pyroxenes, and less common biotite, ilmenite, magnetite, etc.
Lastly, mafic magmas, like basaltic magmas, will have plagioclase, augite, olivine, and, less often, hornblende or Ilmenite.
2. Physical properties
Volcanic ash is grayish but can be blackish or light gray, depending on its composition.
It is highly abrasive, mildly corrosive, and conducts electricity when wet. Fresh ash will feel harsh, smelly, gritty, and unpleasant.
Here is more on its components, grain size, appearance, and density.
1. What is volcanic ash made of?
Volcanic ash comprises glass shards, pumice, lithic or rock fragments, and mineral crystals or mineral crystal fragments. They can be juvenile (from erupting magma), cognate, or accidental.
Lithic particles are non-magmatic, i.e., they have torn from country rock.
On the other hand, mineral and mineral crystals include phenocrysts and those torn from rock walls, i.e., xenocrysts.
The glass includes sideromelane to tachylite in low-viscosity Hawaiian or Strombolian. Highly viscous magmas will have to pumice. Some glass shards may have microlites, or some particles may be fine-grained.
Lastly, phreatic eruption may have altered lithic and mineral fragments in a clay matrix. Also, particles may be coated with crystals of zeolites or clay.
2. Grain size
Volcanic ash particles are less than 2mm to as small as 1μm. Grain sizes are further classified into coarse ash that measures 1/16mm to 2mm and dush or fine ash measuring less than 1/16mm.
Usually, those from low-viscosity magma tend to be coarser than those from highly-viscous magma.
Reasons include higher explosive energies due to increased viscosity and volatiles. Another reason is a communion of rising tephra in the vent.
3. What does it look like?
Volcanic ash particles have varying vesicularity (vesicle volume). These particles may be angular, jagged, sub-rounded, equant, blocky, elongated, crescent, or droplet-like. Others may be pyramidal, elongated, spine-like, or sharply pointed.
Their surfaces may be smooth, flat, pitted, or scalloped. Some will show irregular or conchoidal surface fractures.
Low-viscosity magma will form drop-like glass shards that may be twisted or elongated and often fluidal, smooth surfaces. These drop-like shapes can also be oval, teardrop, dumbbell, spherical, and other shapes. Sometimes, these magmas may form Pele’s hair.
On the other hand, those from viscous magma will have shapes dependent on the shape of the vesicles. They may be oval, tubular, or elongate. Those with broken vesicles may form troughs, cuspates, concavities, and tubes.
Also, high-viscosity magmas tend to have angular, subrounded, or equant lithic or rock fragments.
Lastly, those from phreatomagmatic eruptions may be blocky or pyramidal. Also, rapid quenching may result in plate-like, spherical, drop-like, convoluted, moss-like, smooth surfaces.
4. Densities
It depends on the specific particle. Pumice will be 0.7-1.2g/cm3, glass shards 2.35-2.45g/cm3, mineral crystals 2.7-3.3g/cm3 and lithic particles 2.6-3.3g/cm3.
5. Mohs hardness
Volcanic ash’s Mohs hardness is about 5, which reflects glass and pumice, its main components. This and its angular and jagged shapes make it very abrasive.
How does volcanic ash form?
Volcanic ash and other tephra or pyroclast form during explosives like Plinian, Vulcanian, or Peléan. Even Hawaiian and Strombolian can be explosive.
Also, phreatomagmatic eruptions, phreatic eruptions, and pyroclastic flows can fragment and produce these ashes.
Explosive eruptions occur when rising magma depressurizes. Depressurization makes trapped volatiles suddenly exsolve gases and violently expand or explode.
The violently expanding gases will fragment and eject this ash and other tephra into the air, forming a volcanic plume or column. It is more like when you pop champagne.
On the other hand, the phreatomagmatic eruption occurs from the interaction of magma and ground or near surface water. The interaction will flash water to steam, fragment magma, and cause a steam explosion that will eject steam, water, ash, and other tephra.
The other eruption that forms ash is phreatic. It works just like phreatomagmatic. However, in this eruption, hot magma, rock, and volcanic materials will suddenly boil water, causing a steam explosion. This explosion will fragment and eject pyroclasts, steam, and water.
Lastly, the ground-hugging, rapidly flowing pyroclastic currents can fragment the tephra, forming a volcanic ash plume. Also, heat conservation during this flow can aid in this fragmentation.
Dispersion
Volcanic ash particles form part of a column or plume ejected during an explosive volcanic eruption. This column can go over 30 kilometers high.
As the column rises, it sucks more air reducing its bulk density to a point it is the same as the surrounding.
At this point, the column will stop rising, and the wind will start dispersing ash laterally. The lateral dispersion forms an ash cloud buoyed by air resistance. Very fine particles will have clouds resembling meteorological clouds.
Particle size, column height, and weather conditions like the strength of wind and humidity will determine how far the ash disperses.
It can travel thousands of kilometers or even circle the Earth. For instance, the 1991 Mount Pinatubo eruption in the Philippines produced ash that didn’t settle completely until 1994 or 1995.
The low density of vesicular particles contributes to the far dispersion.
Of course, during the ascend and dispersion, heavier particles will fall closer to the vent. The lightest will go farthest. This happens by gravitation sorting.
Lastly, depending on the amount of ashfall, it may form an extensive ash field or plain.
10 Volcanic ash effects or impacts
Volcanic ash can have effects or impacts on humans and animals, including health. Also, it can contaminate water, disrupt sewers, and affect crops, the environment, and the climate.
More effects include disruption and damage to power systems and minor damage to vehicles, machinery, and electronics. Also, it has an impact on communication and air transport systems.
Communities near eruptions stand the worst impacts. This ash has buried villages and towns before. Also, it has resulted in deaths.
Did you know that ash and pyroclasts hitting the ocean displace lots of water and cause about 20% of volcanic-trigged tsunamis? Now you do.
Here is more on the effects of these ashes:
1. Cause health issues
Volcanic ashfall may cause heart or respiratory health issues, including irritating airways. These include asthma, emphysema, and chronic bronchitis. Also, it may irritate the skin, nose, and eyes.
The various effects depend on the composition, grain size, and chemicals coating their surface. Most are temporary unless the exposure lasts for a long.
Usually, children, older people, or those with pre-existing conditions are most vulnerable.
Lastly, excessive fluorine may cause health issues in water. Others, like iron, aluminum, and manganese, are harmless. However, they may form brown, reddish, or black color on whiteware.
2. Roof collapse
Accumulation of thick ash can overload some roofs. This can make them collapse and cause deaths or injuries. Collapse of roofs killed 300 people during the 1991 Mount Pinatubo eruption.
Flat-topped roofs are particularly vulnerable as the ash won’t slide down. Don’t assume volcanic ash is light; a square yard of four-inch-thick ash can weigh up to 200 pounds. When wet, it will measure 50-100% more.
Besides roof collapse, the ash will clog gutters and contaminate rainwater harvested from roofs.
3. Failure of electrical power systems
Wet volcanic ash conducts electricity. Therefore, it can cause short circuits in electrical power systems, including transformers and high-voltage electronic components. This will disrupt power, including in critical facilities in hospitals.
Also, it will erode, scour, or pit metallic moving parts like turbines and transformer cooling fans.
Lastly, huge accumulations may break steel towers and power lines.
4. Machinery and electronic equipment damage
Volcanic ash may clog air filters of internal combustion machinery or air conditioning equipment. This can make them overheat and get damaged.
It can damage any electronic equipment that circulates external air if it enters buildings or houses. This includes computers, space heaters, etc.
Also, ash may jam mice, keyboards, and touchpads. However, such can be cleaned with compressed air.
Lastly, it can damage moving machinery parts like gears, bearings, etc.
5. Affect transport and airport operation
Volcanic ash will disrupt sea, road, and railway transport. It will cause abrasion to most surfaces, especially on movable parts, and reduce visibility, making driving dangerous.
Also, it may clog oil and air filtration systems, make roads slippery, and cover road markings when wet.
That is not all. Driving fast on ash-covered roads will stir huge clouds, further affecting visibility.
Similarly, it will interrupt airport operations by reducing visibility and making runways and automobileways slippery.
Also, it may damage electrical and communication systems, buildings, parked crafts, etc, at these ports.
6. Damage and interfere with aircraft operation
Volcanic ash will limit aircraft visibility and even cause jet engines to fail. Also, it can cause total power outages and damage control systems. Abrasion of front windows will further reduce visibility.
Jet engines fail to stall because the ash melts due to temperatures exceeding 800°C (1472°F) and later freezes on blades or other parts. Also, abrasion may contribute to failure.
A good example is the 1989 encounter of Boeing 747 with more than 300 passengers onboard with volcanic ash from Redoubt Volcano in Alaska.
The ash clogged and stalled all four of the jet’s engines. Luckily, the pilots successfully restarted the engines and made an emergency but safe landing in Anchorage.
Other notable incidents where ash disrupted or damaged commercial airlines include the eruptions of Kelud, Java, Indonesia, 13-02-2014, Soputan Sulawesi, Indonesia, 19-05-1985, Galunggung, Java, Indonesia 24-06-1982 and 13-07-1982.
There are many other similar incidents. Some resulted in the cancellation or diversion of flights.
So far, there have been no fatalities. However, aircraft and volcanic ash encounters have resulted in hundreds of millions of dollars lost due to aircraft damage, unscheduled landings, increased flight time, and fuel consumption.
7. Drinking water and wastewater systems
Volcanic ash effects on drinking water supplies include damaging well-head pumps. Also, water treatment plants may block water intake channels, damage pump impellers by abrasion, and overload the pump motor.
If it reaches the filtration system, it will increase maintenance costs.
For those who rely on rainwater, this cash may contaminate drinking by introducing harmful chemicals. Also, it may make it acidic, making it more corrosive to anything it encounters.
Lastly, this ash will often find its way into sewer lines. This will damage the prescreening equipment. Also, if it penetrates deeper, it will increase sludge and reduce the capacity of bioreactors.
8. Affect climate
Airborne volcanic ash reflects sun energy to space. This results in a temporary cooling of the atmosphere. Also, it may have effects on the climate.
For instance, the 1783 Laki eruption in Iceland may have resulted in drought in India and the Nile River Valley. Also, it brought the longest winter in New England’s history in 1784.
Similarly, Indonesia’s Mount Tambora eruption in 1815 resulted in a year without summer in 1868.
9. Disrupts communication
This ash will affect signal strength and damage equipment. Also, it will create increased demand that will overload communication networks.
Equipment damage results from direct ashfall. If thick, it may overload and cause communication lines, cables, masts, antennae dishes, or towers to collapse.
10. Environment, crop, and pasture effects
Volcanic ashfall in water may affect aquatic plants and organisms, including fish.
Also, it may cause minor to severe damage to young forests and crops. The damage depends on ash fall thickness, crop types, their maturity stage, and how soon it rains afterward.
That is not all. Fluorine contamination in water and pastures can harm aquatic animals and livestock.
Also, ashfall can damage pastures or reduce their palatability. Such pastures will damage their teeth by abrasion.
Sometimes, it can completely cover pastures, forcing livestock to eat anything poisonous. Also, this will affect agriculturally productive land.
Lastly, this ash can accumulate on sheep wool and damage it. Also, it will add weight to sheep.
Mitigating volcanic ash hazards
The first step to avert and reduce the effects of this ash is monitoring, public advisory alerts, and warnings. Also, a community emergency response team will be in handy.
National Oceanic and Atmospheric Administration (NOAA) meteorologists in the US monitor and track volcanic ash and gases in volcanic plumes. Also, they issue advisories and warnings concerning ashfall or airborne.
Here is how to minimize potential hazards:
1. In case of a forecast
- If there is a forecast, stay home if possible or go home as soon as possible.
- Buy any supplies you may need in case the ashfall takes a long.
- Have at least one supply kit per person in your home, car, or office.
- Move pets indoors and domestic animals to shelter or cover
- Make sure you have enough medicine for people with respiratory issues.
- Move your machinery or vehicle to cover or cover them with a tarp.
- Disconnect downpipes for harvesting roof water.
2. During eruption or ashfall
In case of an eruption or ashfall, stay calm. Don’t spread false news, cause an alarm, or overload communication systems.
Secondly, the American Lung Association recommends you stay indoors. While indoors, you should shut their fireplace damper, doors, windows, duct tape, and any drifty windows.
Also, place a damp towel on door thresholds and cover any air vents with a cloth. A damp one will be perfect.
If using air conditioners or heat pumps that allow air into the house, shut them down or put them in recirculatory mode. This prevents sucking dust-laden air from outside that can clog or damage your air conditioner.
People outside should immediately find a safe shelter, such as a house or car. If possible, go home as soon as possible.
Also, you should use masks, if possible, true HEPA filtersor those with an N-95 rating. However, an ordinary dusk mask or a piece of cloth can reduce how much dust you inhale but may not protect against the very fine dust.
People who use contact lenses should switch to eyeglasses as friction between contact lenses and dust can damage their eyes. Also, consider safety goggles.
That is not all. Avoid driving, and if you must, drive slowly with shut windows. Additionally, put your air in recirculatory mode.
Lastly, call your doctor or an ambulance in case of wheezing, heavy chest, dizziness, lightheadedness, breathing difficulties, or shortness of breath.
3. After eruption or ashfall
Stay indoors, following trusted new channels for updates. Don’t go outside yet until local officials say it is safe to do so.
Also, continue protecting your nose, mouth, and eyes until all the dust settles and is cleaned. This may take a while.
Volcanic ash uses
Uses include ancient and modern, including in age determination.
1. Ancient uses
Romans made pozzolanic cement from volcanic ashes and slacked lime.
Also, this ash may have had uses in ceramics.
2. Modern uses
Some modern volcanic uses include cement, concrete, geopolymer, and ceramic material manufacture. Also, they have applications for adsorbents and stimulating lunar soils.
More uses include abrasive soaps, rubber erasers, industrial filter materials, and fillers in some paints. Very fine ash can help polish plate glass and act as an abrasive additive in toothpaste.
That is not all. Soil enrichment is another key use of this ash. It weathers to form fertile, loamy soils.
Last but not least, volcanic ash use hasn’t been exploited. It has many other potential uses. However, their diverse mineralogy and chemical compositionlimit usage.
3. Helps in age determination or dating
Ashfall can preserve fossils. Thus, they can help scientists know prehistoric events, cultures, ancient environments, and ecosystems.
Also, when in between sedimentary rocks, they can help correlate strata as they are instantaneous geological events or stratigraphic markers.
Furthermore, geologists can also know the age bracket of the layers using radiometric dating.
Lastly, tephrochronology is the scientific dating method that uses discrete layers of tephra and volcanic rocks in sedimentary layers,
Notable volcanic ash eruption examples
- Massive Yellowstone caldera eruption of 600,000 years covered the western USA with ash.
- The 79 CE eruption of Mount Vesuvius produced ash and other pyroclasts that buried Pompeii. Its excavation shows ancient Roman life.
- On May 2, 2008, Chile’s Chaitén volcano produced a 20 km-long plume going to Argentina and the Atlantic Ocean. It disrupted water supply, ground, and airline transport.
- May 18, 1980, eruption of Mount St. Helens
- Mount Mazama ~7700 years ago in Oregon
- In 1815, volcanic ash from the Tambora volcanic eruption in Sumbawa, Indonesia, killed 12,000 people. Later, the death toll rose to 70,000 from the impact of released gases on agriculture.
References
- Kusky, T. M., & Cullen, K. E. (2005).Encyclopedia of earth and space science. Facts on File.
- Prata, F. & Rose, N (2015). Volcanic ash hazards to aviation. In Sigurdsson, H. (ed.)The encyclopedia of volcanoes(2nd ed. pp 911-934). Elsevier Science Publishing Co. Inc.
- Fisher, R. V., & Schmincke, H.U. (1984).Pyroclastic rocks(1st ed.). Springer-Vlg
- Plummer, C. C., Carlson, D. H., & Hammersley, L. (2016).Physical Geology(15th ed.). McGraw-Hill/Education, Inc.
