How do the hot springs on the floor of Yellowstone Lake compare to deep seafloor hydrothermal vents?

Aug 05, 2023

Hydrothermal vents on the ocean floor, like the famous "black smokers," and those on the floor of Yellowstone Lake have some general similarities, but they are also characterized by different types of fluid chemistry and mineral deposits.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Pat Shanks, research geologist emeritus with the U.S. Geological Survey.

Discovery of hydrothermal systems on the ocean floor in the late 1970s is regarded as one of the greatest scientific finds of the 20th century and has implications for the flux of chemicals and heat into the oceans, the formation of some mineral deposits, and the origin of life. Over the last 50 years, deep-ocean hydrothermal vents have been found along plate boundaries throughout the oceans of the world.

Hydrothermal vents also occur on the floor of Yellowstone Lake, and the lake's hydrothermal systems have been the focus of much recent research. USGS studies of hot springs on the floor of Yellowstone beginning in 1999 used multibeam sonar mapping and seismic reflection profiles of the lake floor coupled with direct observations using submersible remotely operated vehicles (ROVs). These studies discovered hundreds of vent craters related to previously active hydrothermal vents and dozens of currently active hot springs. More recently, the multidisciplinary "Hydrothermal Dynamics of Yellowstone Lake" project, which was funded by the National Science Foundation, the Global Foundation for Ocean Exploration, the National Park Service, and the U.S. Geological Survey, provided additional insight into the geology, geochemistry, and geophysics of the vent systems.

Several different types of hot springs have been sampled by ROV on the floor of Yellowstone Lake. The deepest and one of the most active venting areas on the lake bottom, called the Deep Hole vent field and located east of Stevenson Island, had temperatures up to 174 °C (345 °F) and is driven by a vapor-dominated (H2O-CO2-H2S) zone that occurs about 15 m (49 ft) below the lake floor. In contrast, there are lake floor hot springs that have higher chloride content in Mary Bay, Elliott's Crater, and in West Thumb.

So, how similar are Yellowstone Lake hydrothermal vent systems to the famous "black smoker" deep-ocean hydrothermal vent systems? There are several commonalities. Both systems are heated by magmatic bodies at depth, with hot water rising buoyantly and transporting chemicals dissolved by reactions with hot rocks and gases picked up from magma. In both types of systems, as deeply circulating and heated fluids rise toward the seafloor or lake floor, these fluids continue to react with surrounding rocks or sediments and cool. As pressure decreases, they can separate into two phases: a vapor-dominated gas-like fluid and a denser fluid with the properties of a liquid. Mixing colder fluids that circulate through the lake- or ocean-floor rocks may occur at any depth but is more common in the shallow subsurface or within the hydrothermal vents themselves. Hydrothermal fluids from either the seafloor or lake floor form buoyant plumes as they vent into the water column.

But the Yellowstone Lake and seafloor hydrothermal systems also have some important differences, including:

In summary, while they share general similarities, hot springs on the floor of Yellowstone Lake and on the seafloor have differences in physical (depth, pressure, temperature) and geochemical conditions (freshwater vs seawater; iron- and sulfur-rich basaltic rock vs silica-rich rhyolites) that result in vastly different chemical fluxes and deposits.

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