Updated: Jan 20, 2020
Volcanic ash is frozen lava, but on a very small scale. As it’s mostly made of silicon compounds, much like sand on the beach is, when it freezes from its molten state, it does so at such a rapid pace that it becomes a glass. Each individual fragment can be no longer than two millimetres across, but they’re often far finer than that.
Although it does tend to be quite buoyant as individual particles – or even in its larger clumps, known as “lapilli” – it’s actually incredibly dense, roughly five to six times that of rainwater.
This is one particularly insidious way in which volcanic ash can kill you, but generally speaking, inhaling it will be the primary cause of people pushing up the daisies. Remember, you’re inhaling glass, so at the very least, the ash is lacerating the insides of your bronchioli, alveoli and capillaries.
This, as you can imagine, is not a particularly pleasant sensation. In the long-term, it can cause silicosis, an ailment that results in potentially permanent scars to your lungs. If the ash falls into the water supply and people drink it, the same painful condition affects their digestive system too.
There are a fair few toxic aerosols trapped within most volcanic ash too, including hydrogen sulphide – that eggy scent you get with rotting meat or terrible indigestion – sulphur dioxide, and hydrochloric and hydrofluoric acid.
At best, this can cause a shortness of breath and excessive coughing. Enough of these corrosive substances can cause your eyes to start to bleed, and your corneas can get worn down, which makes conjunctivitis more likely to follow. In terms of your respiratory system, you may get bronchitis.