The biggest recent Net-enabled Fukushima shocker originated in our own backyard. It came by way of a YouTube video shot near Half Moon Bay and posted just before Christmas. From there it has gone viral. (Here's one version, possibly the original judging from the traffic it's gotten, though it misidentifies the location as Pacifica State Beach: Fukushima Radiation Hits San Francisco?)

What exactly does the 7½-minute video show?

It features a man visiting the beach with a Geiger counter, a device that detects the presence of radioactive material (here's one simple description of a counter and what it measures). Typically, a Geiger counter emits a clicking sound when it counts a radioactive particle and gives a readout of "counts per minute" (CPM), the rate of radioactive particles it's detecting. The higher the CPM, the higher the radiation.

The Surfer's Beach video begins in a parking lot, and the Geiger counter shows what's considered to be a normal background level of radiation, about 30 CPM. But when the man holding the counter walks down to the sand, the level jumps and tops out at 156. The man, identified elsewhere as "Dave," says: "And so the width of the sand pretty much the length of this particular beach it looks like is contaminated at least three times over (background radiation levels)."

There's Radiation — But Not From Fukushima

The video has prompted public health officials to look at what's going on at Surfer's Beach. As several local media outlets have reported, both county and state health officials are saying the radiation probably has a natural, local origin. Here's David Perlman in the San Francisco Chronicle, who wrote that tests of sand from the beach "show that the radiation has come from natural sources — most probably from ancient rocks eroded in the bluffs above." The story continues:

"There is no public health risk at California beaches due to radioactivity related to events at Fukushima," the California Department of Public Health said Tuesday.

"Recent tests by the San Mateo County Public Health Department show that elevated levels of radiation at Half Moon Bay are due to naturally occurring materials and not radioactivity associated with the Fukushima incident," it said.

Mark Noack of the Half Moon Bay Review has also been reporting on the video and on what's causing the radiation readings on Surfer's Beach. One of the people he's talked to is Steve Weiss, a Geiger counter designer who lives near the beach:

On Monday, Weiss carried a Geiger counter in each hand for a second survey of Surfer's Beach. As he descended to the waterline, the readings on his gadgets climbed. He tested various spots: the side of the bluffs and the white sand closest to the waterline, both registering levels that were high but not suspiciously so as far as he was concerned. But when he placed the sensors down near a line of black silt along the back of the beach, the meters on both his gadgets spiked. The counters registered about 415 counts per minute. A cpm of 30 is considered the baseline for radioactivity typically found in the air.

“It's not normal. I've never seen 400 cpm when I just wave my Geiger around.” he said. “There has to be something radioactive for it to do that.”

Weiss is no amateur; for 40 years he has made a living designing Geiger counters, most recently for International Medcom Inc. After he verified the hots pot, he took a sample of the dark sediment and sent it to his company's main offices in Sebastopol for analysis.

The company's CEO, Dan Sythe, analyzed the samples. He reported on his own blog, Geiger Counter Bulletin, that the radiation in the sand emanated from radium and thorium — "naturally occurring radioactive materials" — not from the cesium isotope that would show it to have come from Fukushima. Sythe characterized the radiation level as "elevated, but roughly equivalent to some granite counter top material from Brazil." And he said the actual source of the Surfer's Beach material still merits investigation.

So, what's the takeaway?

Concern over the long-term impact of Fukushima is understandable. The disaster is akin to an ongoing experiment that will be teaching us about radiation's impacts for many years to come. At the same time, it's pretty clear there's nothing to the almost daily claims that the West Coast is being blasted, flooded, roasted or fried by Fukushima radiation. For the 10,000th time: Always be skeptical and questioning of what you read on the Net, and look for context and confirmation for any and all claims. We don't exempt our own offerings from that advice either.

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A Bay Area Beach Video Stirs Fukushima Radiation Fears -- But Shouldn't