North America's Yellowstone National Park rests atop the only known active supervolcano in the world. For tens of square miles, underground “plumbing” stretches far and wide, fueling hot springs and geysers alike. Now, researchers take a closer look at how this system functions.
The park contains a host of attractions, including repeating geysers such as Old Faithful, mud pots, acidic steam vents called fumaroles, hot springs and hydrothermal pools. All their seemingly-different features are largely fueled by the same underground processes.
Other than geochemists and geologists, very few people have ever wondered as to where the water that regularly bursts out of Old Faithful comes from. A new investigation has determined that the entire Yellowstone system is probably fueled by a single, large water source.
Investigators with the Menlo Park, California-based US Geological Survey (USGS) say that this source provides water which is constantly mixed, boiled, and made to flow through the plumbing system underneath the massive caldera.
The team found that all the hydrothermal features in the park, regardless of how different they look or smell, are largely divided into two categories – basic or acidic. Experts determine whether a water is acidic or basic by comparing its pH level to that of water (7), which is considered to be neutral.
Therefore, waters that have a pH value below 7 are cataloged as acidic (acid mud pots and fumaroles), while those with a pH above 7 are basic (geysers and hot springs). The later make up about 80 to 90 percent of all the water being discharged from within the park.
“Visitors to Yellowstone and even professional naturalists may not realize that the acid fumaroles and mud pots at Yellowstone represent the steam boiled off of deeper boiling groundwater that ultimately emerges kilometers away,” USGS expert and study team leader, Jacob Lowenstern, explains.
His team's main task was figuring out the same water source can lead to the formation of two water circuits, one basic and one acid. “To answer the question, we looked not just at 'what' but 'how much',” the team leader explains, quoted by LiveScience
“This study is unique because it looks both at the chemistry of waters and gases, as well as the magnitude of their discharges – something that is notoriously difficult to constrain,” he adds.
A 4.6-square-mile (12 square kilometers) watershed called the Heart Lake Geyser Basin was found to be the source of water. This basin contains both acidic- and chlorine-rich waters, and is located deep underground. Its average temperatures are around 205 degrees Celsius (401ºF).
When subjected to intense pressure, such as that found deep under the surface, water no longer boils at its usual temperature. However, the liquid does start to boil as it moves closer to the surface. At the same time, it's made more acidic by picking up sulfuric acid.
The chemical is produced by thermophilic (heat-loving) microbes that live in the rocks and soil. They decompose hydrogen sulfide in order to feed off it, and produce the acid as a byproduct. When condensed, the acid collects in acid pools and mud pots.
The remainder of the water circulates under the surface, mixing up with large amounts of rainwater, and slowly raising its pH levels until it become basic. It then makes its way into geysers and hot springs.
“Yellowstone is one of the largest sources of geothermal heat in the world, and our study is a step in putting together a better understanding of how much heat and gas comes out of it. Yellowstone is enormous, so you pretty much have to work at one part at a time,” Lowenstern adds.
This supervolcano needs to be kept under close supervision, due to the damage it could cause if it erupts. Some believe that such an event will be able to bring about at least a minor global extinction event, all on its own. It last erupted around 650 million years ago.