Caustics in the Virgin River, Utah

August 31, 2017

Caustics_on_ VirginRiver_P1100318 (2)

Photographer: Patti Weeks
Summary Authors: Patti Weeks

This photo captured a caustic network in one of the calm shallows along the shoreline of the Virgin River on the Riverside Walk in Utah’s Zion National Park. The angle of the sunlight was optimum for seeing these refracted caustics on the floor of the shallows. As sunlight enters a body of water, the light rays are refracted or bent, due to the higher density of water than air. Since the surface of this water is wavy, it contains ever-changing concave and convex surface areas. After the light rays pass through the surface at different angles, some rays cross, converge and are concentrated into bright spots of light, similar to the way a lens focuses light. What is seen then are sharply focused, yet constantly moving, lines or curved sheets of light where they intercept the stream bed. The phenomenon of refracted caustics, frequently visible in swimming pools, can be observed in clear, often shallow (generally less than about 7 ft or 2 m deep), gently moving bodies of water with a brightly lit floor. On a side note, in the field of computer graphic design, the understanding of the mathematical principles of light behavior is paramount for simulating and rendering underwater caustics. The results can be remarkably realistic. Photo was taken January 27, 2016.

Photo Details: Panasonic Lumix DMC-ZS7 camera; 49.22 mm focal length; f/4.9 aperture; 1/640 sec. exposure; ISO 160.