Spectacular sight as waterfall 'turns to lava'
Nature photographers wait all year for the moment when the sun aligns with a waterfall - creating the illusion of molten lava.
The celestial marvel happens at sunset in mid-February - if the winter weather cooperates.
On those days the setting sun illuminates one of the park's lesser-known waterfalls so precisely that it resembles molten lava as it flows over the sheer granite face of the imposing El Capitan.
Every year growing numbers of photographers converge on the park, their necks craned toward the ephemeral Horsetail Fall, hoping the sky will be clear so they can view the spectacle first recorded in colour in 1973 by the late renowned outdoors photographer Galen Rowell.
"Horsetail is so uniquely situated that I don't know of any other waterfall on earth that gets that kind of light,'' said Michael Frye, who wrote the book The Photographer's Guide to Yosemite.
"How many are perched on a high open cliff? Most are in an alcove or canyon and won't get the sun setting behind it. Yosemite's special geography makes this fall distinctive,'' he said.
Four decades ago, photographers had only to point and shoot to capture another famous Yosemite firefall - a man-made cascade of embers pushed from a bonfire on summer nights from Glacier Point.
But photographing Horsetail is a lesson in astronomy, physics and geometry as hopefuls consider the azimuth degrees and minutes of the earth's orbit relative to the sun to determine the optimal day to experience it. They are looking for the lowest angle of light that will paint Horsetail the colours of an iridescent sunset as rays reflect off granite behind the water. It materialises in varying degrees of intensity for the same two weeks every year.