By Naturalist Guide Rhiana Peck
Why is the thermal activity in the interior of the park different from the northern range?
In the winter, I drive a snowcoach as an interpretive guide in Yellowstone. I am like the living embodiment of Ms. Frizzle from the Magic School Bus, teaching Yellowstone science and history to first time visitors and veterans of the park. In this rendition, I am driving a souped-up yellow van on monster truck snow tires rather than a transforming school bus. In these conditions, the air of imagination is still present.
Some days, I bring visitors from Mammoth Hot Springs Hotel into the interior of the park to Old Faithful. As we ascend the Mammoth Terraces, I imagine steering a submarine as we float up alongside the thermal features, as that’s what we would have needed about 100 million years ago when the area was a giant inland sea.
Mount Everts, a geologist's dream, sits directly across from the Terraces. It is a resource to help understand the difference between Yellowstone’s thermal features in the northern range and Yellowstone’s thermal features in the interior. As we look out at Mount Everts, our eyes will trace shades of horizontal lines across the mountain face. These rivers of rock are made up of limestone and are part of the geologic evidence of Yellowstone’s ancient inland sea. Limestone is made up of the mineral compound calcium carbonate which is found in pearls and seashells. As we look out and see the bands of limestone exposed, we are looking at the remains of ancient sea creatures!
Now a high desert range, the Mammoth Hot Springs area is home to some of the first thermal features you can visit when entering Yellowstone from the North Entrance. Compared to the rest of the park the thermal features express themselves differently. Unlike the interior of the park, this area does not have geysers.
There are four kinds of thermal features in Yellowstone: hotsprings, geysers, mudpots, and fumaroles. Their expression is dependent on the right environment. Yellowstone thermal features need a consistent source of heat, water, and a natural plumbing system. Thanks to Yellowstone’s volcano, a magma plume heats subterranean water which dissolves minerals and is then channeled through cracks and fissures closer to the earth's surface. Depending on the geologic make-up of an area, the hot, mineralised water will express itself differently.
All geysers are hot springs, however not all hot springs are geysers. The latter is the case at the Mammoth Hot Springs. In the northern range, hot springs do not express themselves as geysers, primarily because of the minerals that make up the geology of the area. From Norris to Mammoth Hot Springs, heated water dissolves calcium carbonate in the plumbing system. When the water reaches the surface it cools and with it, the calcium carbonate separates from the water and deposits in terracing formations we enjoy! I like to think of this process like making a cup of hot chocolate. If you take a hot chocolate packet and stir it in warm milk, the powder will dissolve. However, if you take another packet and stir it in cold milk the content does not mix together, but separates. This is similar to what’s occurring as hot water cools, surfacing on the Mammoth Terraces. Calcium carbonate is a weaker mineral compound than the silica-rich rhyolite found within the interior of the park. These harder minerals allow constrictions to form in the plumbing system that will pressure a geyser to erupt. Nonetheless, the deposition of this area makes it an ever-changing and constantly evolving landscape.
Yellowstone has over 10,000 thermal features. They are diverse and unique. Thermophiles, heat loving bacteria, pH, and mineral content play a key role in the differences between how thermal features express themselves. We have only just begun to unravel many of the geological wonders of Yellowstone’s thermal features! Stay tuned to Mountain Musings as we continue to dive deep into the geology, biology, and human connection, taking you on field trips around Yellowstone. And when you can join us in person, we look forward to sharing Yellowstone's secrets with you.