The Rainbow Spring at the Top of the World

The Grand Prismatic Spring in Yellowstone is the largest hot spring in the United States and the third largest in the world, stretching 370 feet across and plunging more than 160 feet deep. Its extraordinary rings of color, deep blue at the center fading through turquoise, green, yellow, and fiery orange at the edges, are produced entirely by heat-loving bacteria called thermophiles that thrive at different temperatures in the water. The center is so hot and mineral-rich that nothing can live there, giving it that impossible deep blue. From ground level the scale is hard to grasp, but from above the spring looks like a painting that nature had no business making. It sits in the Midway Geyser Basin, open to visitors year round, and on cool mornings the steam rising off the surface makes the colors glow.