Why Volcanic Ash and Wildfire Ash Are Very Different Hazards

They might share the same name, but ash produced in the western wildfires is a very different hazard than ash produced in explosive eruptions.

Terra/MODIS image of the wildfires across California, Oregon and Washington on September 10, 2020.
Credit: NASA.

The western United States is on fire. Large swaths of Oregon, California and Washington have massive wildfires burning over millions of across. The immediate threat to people is the fire itself — we need people to evacuate when the order is given so they can stay out of harms way.

However, the larger hazard might be the wildfire smoke and ash being generated from all this burning (see above). This is a trait that wildfires share with volcanic eruptions because it is the widespread volcanic ash that can cause the most harm. However, wildfire ash and volcanic ash are very different beasts.

Let’s talk about how they’re the same. They both drift in the winds and are driven upwards by thermal gradients — hot material billowing upwards. That might be where the similarities end.

So, how are they different? Wildfire ash is made from burning organic material – stuff like trees. As they burn, they can produce three different materiuals that will drift in the air: char, soot and ash. The first — char — is organic material that didn’t burn all the way. The second — soot — is fine carbon particles from the burning process. The last — ash — is the light colored fine powder left from burning. All three of these materials are carbon rich and ash is also rich in calcium.

Just like pretty much anything else, you don’t wildfire ash and smoke in your lungs. If this material gets deep in your lungs, you can definitely experience permanent lung damage or even die from smoke inhalation. This is doubly so for people with pre-existing conditions like asthma or children.

All this organic material in the air leads to poor air quality many hundreds of miles from the fires. Anyone who has lived in an area with wildfires knows how eerie it can be when the smoke and ash spread over the area. The sky darkens, the air smells of burning wood, and your eyes start watering. Even after the fire, people need to wear masks and gloves when they clean up during and after the fire thanks to all this wildfire ash.

Volcanic ash can lead to much of the same hazards: breathing troubles, eye irritation, contamination of water and food. Yet, it is for entirely different reasons.

Unlike wildfire ash, volcanic ash is not caused by burning (so be a cool kid and never say a volcano is producing “smoke”). Volcanic ash is made of tiny fragments of rock and volcanic glass. It gets generated during an explosive eruption where rock can be pulverized or magma can be shattered. The heat from the eruption helps send the ash skyward with volcanic gases like water vapor, carbon dioxide and sulfur dioxide.

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