What kind of structure is the Eye of the Yellowstone?
The Eye of Yellowstone, aka the Grand Prismatic Spring, is a hot spring. Yellowstone is basically a gigantic volcano. The park is famous for its geysers (like Old Faithful), hot springs, and other thermal features.
"Geysers and hot springs are both fed by groundwater from rain and melted snow that seeps through cracks in the surface and is collected in porous rock underground. The water comes into contact with heat from magma chambers below Yellowstone, which warms the water and sends it back up towards the surface via networks of subterranean “plumbing.”
The big difference between a geyser and a hot spring is that a geyser has an obstruction in its hydrothermal plumbing near the surface. In hot springs, water is allowed to circulate to the surface and move freely, giving off steam and heat. In geysers, constrictions keep the boiling water underground. Steam pushes water up towards the surface, causing a drop in pressure and a subsequent eruption.” via
The unique colors of the Grand Prismatic Spring are due to colonies of bacteria that exist in the different ranges of temperature inside the springs. As light penetrates the mineral rich water, the bacteria show rings of vibrant colors of yellow, green, and rust, which is determined by the temperature and depth of the hotspring. So each ring in of color is a different set of pigmented thermaphiles that exist in its own unique range of extreme temperatures. Crazy right.