New vocabulary for me—not for Skus, with geography/geology background.  It’s on a roadside point-of-interest sign on Highway 395 near Mono Lake, California, explaining the origin of the Long Valley Caldera.

Definition from thefreedictionary.com:  nuée ardente  Plural nuées ardentes:  A fast moving gaseous cloud of hot ashes and other material thrown out from an erupting volcano. Nuées ardentes are often incandescent.

Now I have to find out what “incandescent” means in this context.  I only know it as the kind of light bulb fast becoming old-fashioned.  Google tells me:  “emitting light as a result of being heated:  ‘plumes of incandescent liquid rock’.”

Now I’m guessing the French means “silver cloud,” or maybe not:  I think “argent” is silver, so this would be related to “ardent” and refer to its energy instead of its color.