The grand prismatic spring is the largest hot spring (113m) in the United States and is located in Yellowstone National Park, Wyoming. The spring is part of a much larger hydrothermal system at Yellowstone, in which Yellowstone is recognized as a volcanic plateau that had three cataclysmic eruptions in the past, with the most recent eruption being 70,000 years ago. The grand prismatic spring was formed by the heating of groundwater due to magma reservoirs, heating underlying rock and forcing water to the surface in the form of steam and hot water.

The bright and vibrant colors in the spring are caused by variations in the bacterial colonies located within the spring. The water temperatures in the spring can range from 23°C to 90°C or higher, in which very few select bacteria can survive in high temperature conditions, while lower temperatures typically have a wider range of bacterial species. First observing the centre of the spring, it appears to be a bright blue color, which is due to extreme temperatures (greater than 75°C) causing there to be minimal life present. Therefore, this section of the spring is essentially clear water, with the blue coloration additionally being impacted by the reflection of blue light. However, any life that is present in this portion of the spring is not able to undergo photosynthesis to formulate energy, since photosynthesis can not be carried out at temperatures above 75°C. Consequently, organisms surviving in the centre of the spring must undergo alternative energy production methods, such chemotrophic or heterotrophic processes.

Photosynthesis: a widely used chemical process among plants and organisms to formulate energy

‍Chemotrophic process: A process used by organisms to obtain energy by utilizing chemicals from the surrounding environment

‍Heterotrophic process: A process used by organisms that can not produce their own energy, which involves utilizing organic matter from other organisms or the surrounding environment

On the outer ring of the spring colors of green, orange, brown, and yellow can be observed which is due to the lower temperatures and consequently higher variation in bacterial colonies. In these comparably lower temperatures, bacteria are able to undergo photosynthesis which causes a color change. Photosynthetic organisms contain pigments called carotenoids and phycobiliproteins that assist in the transfer of energy during the photosynthesis process. These pigments in the bacteria create the yellow and brown colors observed in the spring. While the green and orange colors in the spring can be attributed to different absorbance and reflectance rates of light, with the water depth additionally being an important factor. Furthermore, dependent on the amount of ultraviolet sunlight reaching the spring, it will impact the photosynthesis process for bacteria that are present, with lower ultraviolet light causing increased chlorophyl in the bacteria and a more green coloration, while high ultraviolet light yields a more yellow coloration.