Volcanic Ash: Formation and Impact

Volcanic Ash

• Volcanic ash is fragments of rock, mineral crystals, and volcanic glass
• Particles are less than 2 mm in diameter
• Often used loosely to refer to all explosive eruption products
• Formed during explosive volcanic eruptions
• Gases in magma expand and escape violently, shattering the magma
• Ash solidifies in the atmosphere
• Can also be produced when magma contacts water (phreatomagmatic eruptions)
• Ash is transported by wind, potentially thousands of kilometers
• Impacts include animal/human health issues, disruption to aviation, infrastructure (e.g., power, communication, transportation), and building damage

Ash Formation

• Explosive eruptions occur when magma decompresses, allowing dissolved gases to form bubbles
• Bubble formation decreases magma density, increasing its speed upwards
• Fragmentation occurs when bubbles occupy 70-80% of the erupting mixture, violently tearing the magma apart
• Fragmentation forms ash particles that solidify in the atmosphere
• Phreatomagmatic eruptions occur when magma contacts water
• The vapor film collapses, increasing heat transfer, leading to rapid water expansion and magma fragmentation
• Pyroclastic density currents can produce ash
• Particle abrasion within currents reduces grain size, creating finer ash
• Secondary fragmentation of pumice fragments also contributes to ash production

Ash Impacts

• Ash impacts can be physical, social, and economic
• Wide-ranging effects, impacting diverse sectors (e.g., infrastructure, agriculture)
• Impacts depend on ash thickness, grain size, chemical composition, moisture content, and duration
• Vulnerable infrastructure and sectors are particularly susceptible to ash fall events

Human and Animal Health

• Inhaling ash particles (<10 µm) can cause respiratory discomfort, eye/skin irritation, and nose/throat issues
• Short-term effects are not critical for most healthy individuals
• Chronic health risks are possible, like silicosis (exposure to free crystalline silica), a lung disease, but documented cases from volcanic ash are lacking
• Ingestion of ash can lead to dental abrasion and fluorine poisoning (ingesting ash with high fluorine content) causing harm to livestock
• Some animals have experienced diarrhea and weakness resulting from ash ingestion

Volcanic Ash and Infrastructure

• Volcanic ash events have caused significant disruption to transportation, electricity, water, sewage, and storm water systems
• Ash fallout can be sufficient to damage or disrupt a range of important services and infrastructure.