Yellowstone’s scenery originates in its volcanic past. The center of the park is a vast caldera, the residue of volcanic eruptions. Yellowstone has erupted three times over the past two million years. The most recent eruption, about 650,000 years ago, created Firehole Falls near the northern rim of its caldera. The Falls surge over giant lava rocks, a perfect subject for a monochromatic image. I used a fast shutter speed of 1/500th of a second to freeze the churning water into lacy threads of frothy bubbles. The black and white rendering makes the image timeless, which is appropriate to Firehole Falls, itself a product of time.