What is an Ashfall?
Volcanic Ashfall can be defined as the minerals, rock fragments and glasses that are exposed violently during a volcanic eruption in the form of ashes into the atmosphere.
The force created by the gases present in the magma propels the ashes to solidify in the atmosphere in the form of volcanic rock fragments and glass. On this page, students will get an idea about the formation and properties of volcanic ashes. We have also provided information about different types of Valcano.
These ashes also commonly known as tephra includes all the erupted volcanic particles, even the one larger than 2 mm in size. The explosion of this ash in the air has a negative impact on the health of humans as well as animals. As the disruption takes place in a wider aspect, it also greatly affects the infrastructures, buildings, industries, vegetations and cultivations of the nearby areas.
Formation of Volcanic Ash Falls
The formation of volcanic ashes or ashfall is an outcome of a volcanic eruption that takes place due to the expansion of the magma. Magma is the hot molten form of rocks present under the Earth’s surface. On exertion of high pressure, these magma comes out violently in the form of hot bubbling lava which leads to a volcanic eruption. On coming in contact with the air, the magma solidifies in the form of rock fragments and glass known as volcanic ashes. These ashes are minute particle-like which have a diameter less than 2 millimetres.
As a result, the volcanic ash in the air can be carried to a larger area by the winds and falls eventually on the ground creating a layer of a thick dust-like particle around the area of eruption.
The formation of volcanic ashes also occurs as a result of phreatomagmatic eruptions. This kind of eruption takes place due to the contact of the magma with the water bodies, or even snow. This, as a result, forms an insulating vapour film as the boiling point of magma is higher than that of water. The reaction of cold water with hot magma increases the amount of heat transferred, thus, leading to expansion of water and fragmentation of the magma, which later comes out violently through the vents of the Volcano.
Unlike burnt wood ashes, these volcanic ashfalls can be dangerous as they have sharp edges containing very small particles of glass and hardened rocks. There are several harmful effects of volcanic ashes on humans as well as animals. It can lead to breathing problems and irritation of the eyes, lungs and nose.
Composition of Volcanic Ashfalls
Volcanic ashfalls are the hardened form of magma in the form of rock fragments and volcanic glasses after coming in contact with the exposed air. The elements found in the volcanic ashes depends upon the thickness of the ashes along with the chemistry of the erupted magma. But as per the reports, the abundantly found elements in these volcanic ashes includes silicon and oxygen. The dark coloured ashes formed after eruptions mainly consist of 45-55% of silica. This silica is rich in iron (Fe) and magnesium (Mg) content. These ashes are sharp-edged particles that have a thickness ranging from 1-5mm which even goes up to 100-300 mm in adverse conditions.
Apart from the volcanic ashes, volcanic eruption also releases harmful gases into the atmosphere which causes severe breathing problems and irritation to the human eyes and nose. These gases are mainly sulfur dioxide, carbon monoxide and dioxide, hydrogen, hydrogen sulfide and hydrogen chloride.
Effects of Volcano Ashfalls
The effects caused by the ashfalls depends upon the thickness of the volcanic ashes. The thickness of the ashes may range from 1-5 millimetres and in adverse conditions it may be over 100-300 millimetres. Since volcanic eruptions cover a wider area, it greatly affects the nearby area.
Some of the Impacts of Volcanic Ashfalls on the Ecosystem are Given Below:
Volcanic Ashfalls can greatly affect the crop fields and can cause damage to the crops and vegetation.
They also contaminate the nearby water bodies, which as a result affects the marine ecosystem.
Due to its expansion in a large area, it causes damage to the infrastructure including roads, buildings and breakage of telephone and electric polls, thus affecting the normal living of human beings.
As volcanic eruptions release harmful gases such as carbon dioxide, sulfur dioxide and hydrogen sulfide into the atmosphere, it gives rise to breathing inability and irritation of the skin, eyes and nose.
Ashfalls of higher thickness ranging from 100-300 millimetres can lead to collapsing of building, the burial of low plants and severe damage to plantation and trees.
Livestock and other animals are killed every year due to this complete burial of land and soil horizon.
FAQs on Volcanic Ash Falls
1. What exactly is volcanic ash and what is it composed of?
Volcanic ash consists of tiny, sharp particles of pulverised rock, minerals, and volcanic glass, each less than 2 millimetres in diameter. It is not like the soft ash from a fire; it is hard and abrasive. The specific composition varies but often includes silica, feldspar, and other rock-forming minerals. These fragments are created during explosive volcanic eruptions when dissolved gases in magma expand and violently shatter the molten rock.
2. What are the immediate effects of a volcanic ash fall on an area?
A volcanic ash fall can have severe and immediate consequences for the affected region. Key effects include:
- Human Health: Fine ash particles can cause respiratory problems, eye irritation, and skin irritation.
- Infrastructure: The weight of heavy ash, especially when wet, can cause roofs to collapse. It can also clog water and sewage systems and lead to power outages by short-circuiting transformers.
- Transportation: Ash reduces visibility, makes roads slippery, and poses a critical danger to aircraft engines.
- Agriculture: Crops can be buried and destroyed, and livestock may be harmed by ingesting ash-covered vegetation.
3. How is a volcanic ash fall different from a pyroclastic flow?
While both are dangerous volcanic hazards, they are fundamentally different. A volcanic ash fall is the widespread deposition of ash particles that are ejected high into the atmosphere and carried by wind, settling over large areas like a heavy snowfall. In contrast, a pyroclastic flow is a ground-hugging, fast-moving avalanche of hot gas, ash, and larger rock fragments that travels at immense speeds down the volcano's slopes and is intensely hot, incinerating everything in its path.
4. Why is volcanic ash considered a major hazard for modern aircraft?
Volcanic ash is extremely dangerous for aircraft for several reasons. The abrasive particles can scratch cockpit windows, impairing visibility, and can clog critical sensors on the exterior of the plane. The most severe danger occurs when ash enters jet engines. The high temperatures inside the engine can melt the ash, which then solidifies on turbine blades, disrupting airflow and potentially causing the engines to stall and shut down.
5. Can a major volcanic ash fall affect global climate patterns?
Yes, a large-scale eruption can influence global climate, primarily causing a temporary cooling effect. Fine ash particles and sulfur dioxide gas injected into the stratosphere can form a veil that reflects sunlight back into space, reducing the amount of solar energy reaching the Earth's surface. This can lead to a noticeable, though temporary, drop in global average temperatures for one to three years following the eruption.
6. How far can volcanic ash travel from its source volcano?
The distance volcanic ash travels depends on the power of the eruption and prevailing wind patterns. Large, coarse particles tend to fall closer to the volcano, within a few kilometres. However, very fine ash particles can be carried by high-altitude winds for thousands of kilometres across continents and oceans. For example, the 2010 eruption of Eyjafjallajökull in Iceland spread an ash cloud that disrupted air travel across Europe for weeks.
7. Are there any positive impacts or uses for volcanic ash?
Despite its hazards, volcanic ash has some beneficial uses. Over the long term, the weathering of volcanic ash layers creates exceptionally fertile soils that are rich in minerals, making volcanic regions some of the most productive agricultural areas in the world. Additionally, ash can be used as a raw material in manufacturing, such as in the production of lightweight concrete, bricks, and as a fine abrasive for industrial polishing.
8. What is the most famous example of a city destroyed by volcanic ash?
The most famous historical examples are the Roman cities of Pompeii and Herculaneum. In 79 AD, the eruption of Mount Vesuvius buried these cities under a thick layer of ash and pumice. The ash fall happened so quickly that it preserved buildings, objects, and even the final moments of residents, providing archaeologists with a unique and detailed snapshot of Roman life.
9. Beyond human health and infrastructure, what are the long-term environmental consequences of a major ash fall?
The long-term environmental impacts of a major ash fall can be significant. Initially, the ash can make soil and water bodies acidic, harming aquatic life. It can clog rivers, leading to flooding, and drastically alter landscapes. However, over decades and centuries, the chemical breakdown of the ash releases vital nutrients into the ecosystem, leading to a period of enhanced soil fertility and vigorous regrowth of vegetation, completely reshaping the local ecology.
