Over the past decade or so, researchers have discovered many new features on the lake bottom, including a vigorous hydrothermal system that would make for an impressive geyser basin if it were on land. In fact, the hottest hydrothermal vent temperatures measured anywhere in the Park were on the lake bottom—170°C (340°F)! What else might the lake be hiding beneath its surface?

Hot springs, geysers, and fumaroles in and around Yellowstone Lake serve as constant reminders of the volcanically and seismically active Yellowstone Caldera below. The numerous active hydrothermal vents on the floor of Yellowstone Lake are a significant part of the world's largest continental hydrothermal system—there are over 10,000 documented active thermal features in Yellowstone National Park. The region is also one of the most seismically active areas in the intermountain west, has greater than typical heat flow values, and has high rates of precipitation due to its relatively high elevation. Understanding the cause-and-effect relationships between environmental conditions and activity, as well as annual changes in lake level, can yield valuable insights into subsurface processes that are otherwise difficult to observe.

A research team has embarked on a multi-year project to understand how the Yellowstone Lake hydrothermal system responds to geological and environmental forcing. The Hydrothermal Dynamics of Yellowstone Lake (HD-YLAKE) project has major funding and logistical support from the National Science Foundation, the Yellowstone Volcano Observatory, the U.S. Geological Survey, and the National Park Service. The main goals of the project are to understand the relationship between the long-term history of hydrothermal activity in Yellowstone Lake and its influence on aquatic ecosystems and climate-driven processes in the lake and its watershed.

The team is using a two-pronged approach to address these goals. First, they are conducting geophysical and geochemical monitoring of the active system to assess changes over time. Second, they are collecting and analyzing sediment core samples from the lake bottom to study the postglacial (<15,000 year) geologic and climatic history of Yellowstone Lake. This work involves using a research vessel, the RV Annie, as well as a remotely operated vehicle, named Yogi, to study the lake bottom and collect samples.

Over the past few years, the research team deployed a network of pressure–temperature gauges, heat flow equipment, and seismometers on the lake floor. The most intensive work began in the summer of 2017, when they deployed a full-scale network of monitoring instrumentation, including 10 lake-bottom seismometers and two chemical sensors. Equipment will be recovered in August 2018, after which time data analysis can begin.

In addition, the team collected sediment gravity cores from the top 1 m (3 ft) of the lake bed, sediment piston cores that extended as much as 12.1 m (~40 ft) into the lake bed, gastight samples of hydrothermal fluid from thermal vents, and samples of microbial material.

Preliminary examination of the piston and gravity cores reveals that many contain multiple hydrothermal explosion deposits, suggesting a history of repeated small explosions from the Yellowstone Lake area (this confirms previous study of on-land deposits). Analyses are currently under way to determine mineralogy and composition of the sediment. Geochemical analyses of samples of fluid from within the cores will provide information about the composition of hydrothermal waters that exist below the lake floor and will the extent of the lake-bottom hydrothermal vent fields. Finally, studying single-celled organisms, pollen, charcoal, and tephra preserved in the cores will link the aquatic response of the lake to past climate, hydrothermal, and geologic activity.

More information about the HD-YLAKE project can be found here . Stay tuned to Yellowstone Caldera Chronicles for more information on research results as analyses are completed and equipment is recovered in 2018!