That bright glow that appears to be lava? Don't worry. It's just light reflected on the Horsetail waterfall. The phenomenon referred to as the Yosemite Firefall, the Chronicle writes, is just observable twice a year or so. It was recently captured by photographer Sangeeta Dey, who explained the fortuitous shot to Facebook:

This is the Horse tail waterfall in the Yosemite National Park. Every year for two weeks in February, the sun sets at a certain angle and illuminates the waterfall in luminescent orange and red, making it look like a fluid fire. I’ve met photographers who said that they have been coming for 11 years only to see this happen 2 or 3 times.

The phenomenon was supposed to happen at around 5:30 in the evening, but I was there at 2 PM to find a spot. I finally settled for a tiny space under a thorny bush. When the fall started glowing, I couldn't believe what I was seeing. For 10 minutes, all of us sat there mesmerized by this spectacle.When it ended, a few of us had tears in our eyes. Some people were clapping. And others were just ecstatic to finally get a chance to see it after trying for years.

Some others were lucky as well:

No that's not lava! That's #HorsetailFalls as it was captured this past Saturday by @_gnarlynick and shared with @yosemitenation This beautiful #natural phenomenon known as the #firefall only occurs for a few weeks in late February. As the #highcountry #snow begins to melt it begins to trickle down next to #ElCapitan and as the #sun sets during this particular time of year, this cascade captures the alpine glow of the #Sierras turning this very seasonal #waterfall into a spectacular site to see! Join us this #Saturday as we'll be staying till #sunset on our #SeasonsofYosemite adventure to see if we can witness this light show ourselves! #VisitSacramento #YosemiteValley #AlopexEcoAdventures #Sacramento to #Yosemite #LetUsDrive

A photo posted by Alopex Eco Adventures (@alopexadv) on

CBSSF tells us that images of the natural phenomenon were first captured in 1973.

A photo posted by @archanjm on

It's also said that the firefall started as a manmade spectacle when, during the 19th century, a campfire was pushed over the cliff, a ritual continued until 1968.

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