To log this EarthCache, send me the following answers:
1. Post a picture of yourself (face not required) or a personal item at the spring.
2. Explain in your own words why the colors form here at the spring.
3. Find some geyserite and describe it.
Way below the surface of Yellowstone National Park, the groundwater is heated by magma. As the water rises to the surface, it will come in contact with the rocks and the minerals below. The water now will have dissolved minerals in it that will change how it interacts with rocks near the surface that we see.
The Grand Prismatic Spring was formed in the Midway Geyser Basin when the heated water from the underground rises to the surface with the dissolved minerals in it. The rock below the surface is rhyolitic lava flows. As water travels through the rock, it dissolves silicia in the rhyolite. Silica is a common mineral that is dissolved during this process. Other minerals are calcium carbonate and sulfides. When the water reaches the surface, the temperature begins to cool and it loses the pressure. This causes the dissolved minerals to precipitate and form the colorful crust of silica deposits that are seen around the edges of the spring.
At the surface, the silica will form siliceous sinter which makes the edges of the spring. They are called geyserite.
The Grand Prismatic Spring is the largest hot spring in the US, and the third-largest in the world. So why are you seeing so many colors at this spring, unlike others in the park? You can see blues, greens, yellows, oranges, and reds along the edges. There are thermophiles (heat-loving bacteria) in the waters that will form microbial mats. A prismatic effect scatters the light off the mats and produces the colors that you see.
Humans can change the entire coloration process. We must take care to not leave boardwalks in this area and stay off the microbial mats. Soil erosion and littering also can change it.
So explain to me how the coloring works? The water will have different temperatures as it rises to the surface and interacts with the cooler rocks. The very hottest water is in the center and it cools as it spreads out. The water is around 189 degrees F in the middle. This section is so hot that most organism cannot survive here. So this causes the water to look very clear and looks almost blue as the blue wavelengths of light scatter (same reason oceans and lakes look blue).
The first section outside of the middle appears yellow. This water is slightly cooler than the middle at 165 degrees F. A bacteria call synechococcus lives in this temperature band. They produce carotenoids to protect themselves from the sunlight and temperatures. This causes the yellow color.
The next section is the orange band and is around 149 degrees F. They produce different types of cartenoids so it appears orange here.
The outermost section is about 131 degrees F and has the most types of bacteria because of the cooler temperatures. All these types of bacteria that live here have various cartenoid production and the mixed colors are the red brown that you can see.
To log this EarthCache, send me the following answers:
1. Post a picture of yourself (face not required) or a personal item at the spring.
2. Explain in your own words why the colors form here at the spring.
3. Find some geyserite and describe it.
sources: geologyscience.com; smithsonianmag.com; NPS Yellowstone