Calcite Springs, a thermal feature in the northeast corner of Yellowstone National Park, is one of the park's lesser-known thermal features.
It’s a beautiful exposure of white calcite crystals and steam vents on a sheer cliff cascading into the pristine waters of the Yellowstone River below.
However, sharp-eyed onlookers will notice streams of a gloopy, black, tar-like substance streaking the side of the white cliff, often rolling into giant, ugly balls. It’s seemingly out of place and unsettling, blemishing the otherwise serene surface.
Some will tell you it’s rivers of brimstone from the depths of hell, while others say it’s a vein of black gold, revealing untold riches right under the surface.
Actually, it’s both — smoldering, sticky, super smelly and completely natural.
The Stink Of Sulphur
While there hasn’t been an active lava flow in Yellowstone for hundreds of thousands of years, lots of minerals and other substances are freely flowing throughout the park. One of those free-flowing substances is molten sulfur.
“Molten sulfur isn’t uncommon in Yellowstone,” Mike Poland, scientist-in-charge of the Yellowstone Volcano Observatory, told Cowboy State Daily. “There are several places, including Calcite Springs, where you can find active sulfur flows.”
Sulfur, also known as brimstone, is the fifth most common element on Earth. It’s commonly found in its solid, liquid, and gaseous states near hot springs and volcanoes.
Yellowstone is brimming over with brimstone.
Sulfur deposits are visible in most of the park’s thermal areas, while gaseous sulfur is responsible for the distinctive sour smell permeating the air.
Some of Yellowstone’s thermal basins are hot enough to melt solid sulfur, creating the molten sulfur flows like those streaking Calcite Springs. People might panic when they hear about anything molten in the park, but Poland said it’s not that spectacular.
“The melting point of sulfur is around 239 degrees, which isn’t much higher than the 212-degree boiling point of water,” he said. “It’s not uncommon for a hydrothermal area, like Calcite Springs, to have enough heat to melt sulfur.”
Cinder Pool, a hot spring in the Norris Geyser Basin, got its name from the condensed “cinders” of molten sulfur that used to float at the surface of the water.
It was one of the only cinder-producing thermal pools in the world until it suddenly stopped producing cinders within the last few years.
Poland said molten sulfur often forms hollow spheres as it flows, but they’re usually yellow. Why has the molten sulfur at Calcite Springs turned black?
“When molten sulfur comes into contact with the air, it turns black,” Poland said. “That’s why you get those black deposits.”
A study of the cinders from Cinder Pool revealed another source of black surface sulfur. Sulfur spheres collected from the pool contained pyrite, “fool’s gold,” that was finely dispersed through a layer of molten sulfur at the bottom of the pool that (used to) produce the cinders.
“It’s a common aspect of the geothermal system that you see in Yellowstone,” he said.
So, that explains the black streaks of molten sulfur and “fool’s gold” at Calcite Springs. But what about the “black gold?”
There’s Oil In Them Thar Springs!
Petroleum is one of Wyoming’s biggest businesses as it’s extremely abundant throughout the state. That includes Yellowstone, although Poland said it’s comparatively rarer there than it is in the rest of Wyoming.
“The same oil-bearing geology underlying Wyoming is present in parts of Yellowstone,” he said. “That's a consequence of the whole area being covered by a shallow sea in the past, and when the area collapsed and was covered, you got the production of hydrocarbons.”
Yellowstone is protected from any mineral and fossil fuel exploitation, but that doesn’t stop those resources from exploiting themselves.
According to Poland, there are several spots in the park where an oil seep has breached the surface and started oozing out of the ground.
“They’re more common in the northeastern corner of Yellowstone, which is where Calcite Springs is located,” he said. “Finding petroleum in the park is not unusual or unexpected.”
At Calcite Springs, the presence of petroleum is a little more complex than a surface seep.
A 1990 study found that petroleum flowing at Calcite Springs comes from sedimentary rocks, specifically from the oil-rich Phosphoria Formation, close to but not at the surface.
The petroleum was released from the sedimentary rocks after they were breached and altered by the spring’s hydrothermal water.
Oil doesn’t flow from Calcite Springs. Instead of appearing as a bubbling crude, the petroleum reaches the surface as a “vapor condensate” in the steam vents.
So, unless somebody’s willing to extract oil from steam, there isn’t an easy fortune to be made from tapping into Calcite Springs’ petroleum reserves. That, and it’d be illegal to try.
A Special (And Smelly) Duo
In Poland’s opinion, there’s nothing extraordinary about molten sulfur flows and petroleum seeps in Yellowstone.
What makes Calcite Springs unique is that it’s one of the only places where the two substances can be found in the same spot, fragrantly flowing into the nostrils of tourists together.
“It's a little unusual to see both in the same place, but that's a consequence of the complex geology of Yellowstone,” he said. “That's where molten sulfur and petroleum happen to intersect.”
Calcite Springs isn’t a popular thermal feature, given its location along the sheer side of a canyon. The area’s closed to the public, so the Calcite Springs Overlook, just north of Tower Falls, is the closest most people can get to the unique spot.
Most visitors will pass right by Calcite Springs, but they’ll get a whiff of it as they do. Anybody who likes the smell of sulfur and petroleum together should stop by – assuming such a person exists who can tolerate two bad smells that go worse together.
Poland added that there’s no hazard posed by the mixing of molten sulfur and petroleum at Calcite Springs. It might smell obnoxious, but that’s the only threat it poses to anyone at the overlook.
“There's no real implications to what’s happening at Calcite Springs, other than it's telling you a lot about the geology of the area,” he said. “It shows how the current activity is affecting the geology of the underlying layers. In that sense, it’s unique.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
