SCV Outdoor Report: Pyrocumulus Clouds
By Wendy Langhans
It looked both ominous and somehow familiar - the pyrocumulus clouds that appeared over our Santa Clarita valley almost two weeks ago. It certainly caught my attention, enough so that I went home and grabbed my camera.
It was a pyrocumulus cloud, created by the Station fire. Pyrocumulus clouds get their name from their shape ("cumulus" means "heap" in Latin) and their source ("pyr" means "fire" in Greek). And these clouds DO look like a heap, although I think they sometimes resemble a cauliflower.
Pyrocumulus clouds contain thousands of different kinds of emissions. But I'd like to talk about four major components: water vapor, ash particles, tar particles and soot particles.
- Water vapor comes from two sources, the moisture already in the fuel and the byproduct of combustion. (You may remember that last week, we talked about "live fuel moisture" content, which is the percent by weight of moisture in live plant material.)
- Ash particles are sand-like minerals that remain after combustion. Some of these whitish-colored particles remain on the ground and some are carried aloft and deposited miles away.
- Tar particles result from inefficient combustion of fuel, which is usually due to lack of oxygen.
- Soot particles are clusters of carbon particles that are found inside the flame. When flames are ripped open from the wind turbulence, the not-yet-burned particles of black soot escape into the updraft.
As I take a second look, I now realize why it looks both familiar and ominous. The white, cauliflower-shaped cloud gets it's color and shape from condensing water vapor. It resembles the thunderstorms from my midwestern childhood. And the gray clouds get their color from a combination of black soot, white ash and tar particles. These clouds look ominous because I know where those particles came from - out of the turbulent winds of an uncontained and dangerous wildfire.
Upcoming Outdoor Events:
Saturday, September 19, 8-10 AM Bird walk in Towsley Canyon. All year round, the habitats of Towsley Canyon attract a wealth of birdlife. Beginners are welcome. Bring your binoculars. 2 hours, easy walk. For a map, go here.
You can listen to stories like this every Friday morning at 7:10 a.m. on "The Hike Report", brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.