On the bus, the tour guide showed us 2012 – a Hollywood catastrophe movie with a plot line that partially took place in Yellowstone National Park. The only thing we learned is that a volcano lies within the park. Midway Geyser Basin is located near the center of Yellowstone Caldera.
A half mile boardwalk guides you through the hydrothermal collection at Midway Geyser Basin, which includes the dormant Excelsior Geyser, the largest hot spring in the United States – Grand Prismatic Spring, Turquoise Pool, and Opal Pool. Beneath the boardwalk, spring water overflows rendering an eerie, barren landscape.
Grand Prismatic Spring is the rainbow colored lake often seen in photos and postcards of Yellowstone. However, because the vivid surface has a diameter more than 110 meters long, only the brownish red rim is directly visible from the boardwalk. These warm colors come from bacteria that live in the more than 150°F water. The blue center can be seen reflected in the steam.
On the other hand, the blue and green colors of Opal Pool and Turquoise Pool are easily visible.