1) What are atmospheric rivers? About how often do megafloods impact the California and western states regions?

Long regions in the atmosphere that transport large amounts of vapor, a “river in the sky”. 30-50% of annual precipitation is brought on by these events. According to Ingram, geologic evidence shows a “mega flood” every 100-200 years, although the last one was in 1861.

2) Approximately how extensive was the 1861-62 event in terms of geography? (ie which states and countries were impacted)?

LA received 66 in of rainfall, flooding and creating lakes throughout the Mojave Desert area. Anaheim, and the Santa Ana river flooded. The Sierra Nevada’s received up to 15 in of snow. The Feather, American and Yuba rivers flooded. American river levees failed and flooded Sacramento. “They were the worst in recorded history over much of the American West, including northern Mexico, Oregon, Washington State and into British Columbia, as well as reaching inland into Nevada, Utah and Arizona.” (Ingram)

3) How well do you think the public is aware of the mega flood hazard, compared with earthquake hazards, in California and other western states?

Originally coming from California, I would say that they are oblivious to massive flooding. Growing up and in school I cannot recall ever hearing about this great flooding, or even atmospheric rivers. Earthquakes were the big talk when I was growing up. Coming from the Mojave Desert we knew there was flooding, because any time we had a serious rainfall our town would flood. That was never attributed to extreme weather or anything like that, just the fact that our town was no built to handle that much rainfall. This was a great assignment and it is sad that I am just hearing about this having come from California.

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  1. I agree! I grew up in Santa Barbara and I had never heard of the megaflood phenomena or the 1862 event until I started teaching this course. Even after being a geology major at UC! It’s startling that there has not been more public awareness, but the USGS and other agencies are trying to change that now.

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