The two of us have been watching the news from Los Angeles with a true sense of horror. This has not been a tragedy, nor a disaster, but it has been a true catastrophe. Thousands of homes have burned to the ground. All those people were abruptly forced to pick up their children, their pets, along with a few belongings and flee for their lives. They have suddenly become homeless. All of them are, right this minute, wondering where will they go and how will they ever recover. Some are probably even worrying about where will they sleep tonight. As we write (Jan 9th), we fear that the news will only get worse, perhaps much worse. We can’t do much help all those many people, but we feel a strong obligation that we should try to make clear what has happened to them. We are scientists; we can offer explanations that you should know and also, more importantly, understand. We are grateful to have The Mountain Eagle to encourage us to offer that explanation.
The story begins in something called the Great Basin, a gigantic lowland that covers much of the landscape east of California’s Sierra Nevada Mountains. See our first illustration, courtesy of Wikipedia Commons. Autumns and winters are times of the year when the basin is affected by a prevailing high-pressure system. Think of it as filling up with great masses of heavy air. Whenever there is low pressure along the Pacific coast then “heavy” Great Basin air currents can enter into nearby mountain passes where they can flow southwest and downhill to make their escapes. These become what are known as the Santa Ana winds. You may well have heard of them, but have you understood them? Well, that is our goal here and now.
The southern part of the Great Basin is the Mojave Desert, always a hot and dry landscape. See our second illustration, again courtesy of Wikipedia Commons. It shows masses of air funneled into and descending through four of those mountain passes, lying just southwest of the Mojave Desert and just northeast of Los Angeles. Notice that the artist has tinted them blue to the east, yellow in the middle and red in the west. That shows desert air masses, which had already been warm, becoming even hotter as they descend those four slopes. Air masses always warm up as they descend. At the same time the relative humidity declines; the desert air becomes even drier. As these air masses squeeze into those passes, they must speed up and become hot, dry howling winds – the Santa Ana winds. And, as you and we have seen, there was the whole Los Angeles community, standing in the way
We can guess one of your questions: yes, all this has been known about and understood for many years, even many decades. Why weren’t people better prepared?
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”
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