Here's why ash and aviation don't mix.

Volcanic Ash Isn't Comparable To Smoke

Volcanic ash is made up of tiny particles of jagged rock, minerals, and volcanic glass. It's nothing like flying through the smoke from a fire. Volcanic ash is hard, abrasive, and does not dissolve in water. According to the National Geographic Society, volcanic ash particles are roughly 2 millimeters across.

While relatively uncommon, explosive volcanic eruptions that send ash clouds into the flight levels can affect most major components of airplanes. Meteorologists around the world track the progression of volcanic activity and ash clouds to issue notices and flight restrictions to pilots and airlines.

But even with flight restrictions, incidents still happen. This USGS Survey documents 79 major encounters between aircraft and volcanic ash from 1953 to 2009.

In 2010, plumes spewed out by the Eyjafjallajokull volcano in Iceland caused major disruptions and grounded over 100,000 international flights, costing airlines more than $3.1 billion. Clouds of volcanic ash can spread across thousands of miles, depending on wind patterns and atmospheric stability, making them hard to predict.

Here's a satellite image from a Chilean volcanic eruption:

So, What Happens When A Jet Engine Flies Through Volcanic Ash?

According to a USGS study, the melting temperature of the glassy silicate material in an ash cloud is lower than combustion temperatures in modern jet engines. You can see the problem here: ash particles sucked into an engine can melt and accumulate as re-solidified deposits in cooler parts of the engine. The glass can degrade engine performance all the way to the point of in-flight compressor stall and loss of thrust.

Below, you can see dark, glassy deposits of melted volcanic ash on the leading edge of high-pressure turbine nozzle guide vanes.

Ash Doesn't Just Affect Engines

Beyond ruining jet engines, ash particles can abrade forward-facing surfaces, including windscreens, fuselage surfaces, and compressor fan blades. Ash contamination also can lead to failure of critical navigational and operational instruments.

It can also clog pitot tubes and static ports, resulting in erroneous airspeed and altitude indications. It affects the cabin too. Ash can infiltrate the ventilation and pressurization systems of aircraft, filling the cabin with a sulfuric haze.

The abraded windscreen from a Boeing 747 damaged in the December 15, 1989 eruption of Redoubt Volcano is pictured below. The frosted right side of the glass almost completely obscured the pilots ability to see outside. On the left, the clearer, less-abraded side received only glancing blows from ash particles as the plane flew through the ash cloud. The crew lost thrust from all four engines during their encounter, and eventually made a successful landing in Jakarta.

Volcanic ash is nasty stuff. If you ever find yourself near an eruption, don't push your luck. Make a wide diversion around the ash cloud, and keep your engines and plane running smoothly.