Definition
The release of molten rock, gases, and ash from a volcano into the atmosphere. From an aviation standpoint, eruptions are significant because they can inject large quantities of volcanic ash and corrosive gases to high altitudes, where the ash can drift for hundreds or thousands of miles along prevailing winds and create a serious hazard to aircraft engines, airframes, and flight instruments.
Plain English
When a volcano blows, it throws rock, gas, and fine ash high into the air. That ash can travel a long way on the wind and is dangerous to fly through.
Context Anchor
Seen in instrument weather flying, weather briefings, and volcanic ash advisories when a route may pass near or downwind of an active volcano.
Derivation
From the Latin 'eruptio,' meaning 'a bursting forth.' The word captures the sudden release of material from inside the volcano into the open air -- which is exactly the part pilots need to think about.
Why Pilots Care
Ash from eruptions can cause engine flameouts, pitot tube blockage, and loss of visibility, creating immediate safety threats during instrument flight.
Analogy
Volcanic ash is not like soft fireplace ash. It is more like very fine powdered rock, so flying through it can act like sending the airplane through a cloud of grit.
Grounding Statement
A volcano can erupt in one place, but the ash can be carried by wind into airspace many miles away.
Intuition Check
Do not assume volcanic eruptions only matter if you can see lava or a large explosion. In aviation, even an ash cloud from an eruption can be dangerous far downwind of the volcano.
Example Sentence 1
After the volcanic eruption in the Aleutians, pilots received a SIGMET warning of an ash cloud drifting east at flight levels above 20,000 feet.
Example Sentence 2
Instrument procedures require checking volcanic eruption advisories before departure when ash clouds may affect the route.