The Firefall

 
The waterfall was impossible to see properly from Topside, and from below it was mostly hidden behind a constant shroud of misty spray. But from here, from across the Crevasse and a little to one side, it appeared in all its glory. The full weight and volume of the great river Drasil spread across a vast, slightly curving stretch of granite cliff, tumbling endlessly down in a thin sheet to break into churning froth against the water below.
— Amy Beatty, Dragon Ascending
Photo by paul bica, Niagara Falls, CC BY 2.0,  via Wikimedia Commons

Photo by paul bica, Niagara Falls, CC BY 2.0,  via Wikimedia Commons

In Dragon Ascending, the first book of the Vanir Dragon Series, we catch a brief view of the Firefall at the Edge of the World. This phenomenon happens for only a few days before and after the summer solstice and can be seen only from the Vanahir side of the Crevasse. 

At sunset near the solstice, the golden light of the setting sun shines down the channel between the great islands Vanahir and Faehold all the way to the Edge of the World. When the angle is just right, the light passes through the thin curtain of the waterfall and reflects off the rocks behind it, passing back through the water and making it glow like fire.

 
Photo by Wcwoolf CC BY-SA 4.0, via Wikimedia Commons

Photo by Wcwoolf CC BY-SA 4.0, via Wikimedia Commons

 
When she opened her eyes again, the waterfall was on fire. The sunset light had deepened into gold and crimson, and from this angle it reflected off the stone behind the fall and back through the water, making it glow like a fall of dragon fire.
— Amy Beatty, Dragon Ascending

This fictional phenomenon was inspired by the real-life "firefall" effect that happens at Horsetail Falls in Yosemite National Park (a much smaller waterfall than the Edge of the World) for the last two weeks of February.  When conditions are just right, the sunset light reflects off the rocks, causing the waterfall to glow like fire.

The video below provides additional information about this natural wonder. 

 

Video courtesy of the U.S. National Park Service. [Public Domain]