Studying Yellowstone National Park's Thermal Plumbing

UAV photo showing LaDuke Hot Spring (yellowish orange color in the center) discharging to the Yellowstone River.

Editor's Note: Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory.

Who doesn't enjoy a good, old-fashioned soak in Yellowstone National Park's Boiling River? The Boiling River is the result of a hot spring that discharges into the Gardner River. These hot spring and river interactions create not only unique soaking opportunities, but are also known to affect the ecological and physical characteristics of a river.

Boiling River is not the only place these interactions take place. Just a few miles north of Yellowstone National Park, discharge from a sizable hydrothermal feature, LaDuke Hot Springs, mixes with the Yellowstone River.

Starting in September 2018 and scheduled to continue through August 2019, a team of Montana Bureau of Mines and Geology and Montana Tech researchers is investigating the extent of hot springs and seeps and their seasonal variation in discharge to the Yellowstone River in the area of LaDuke Hot Springs. The team is visiting LaDuke Hot Springs six times over a year, using a combination of aerial and ground-based data collection techniques to measure the hydrothermal features. Motivations for this project include evaluating whether or not researchers can use unmanned aerial vehicle (UAV) temperature data to look at seasonal changes in hot spring discharge, and to see how the river and the hot springs and seeps interact with each other.

The main discharge from LaDuke Hot Springs is collected underground in a chamber or springbox (visible as a white line north of Highway 89 in the photo above), which fills with the geothermal water. The springbox overflow discharges through a culvert under the highway into the Yellowstone River. The discharge and temperature from the springbox are monitored as part of the Yellowstone Controlled Groundwater area.

View of one of the geothermal seeps that flows into the Yellowstone River south of LaDuke Hot Spring.

This study takes advantage of temperature contrasts between the hydrothermal discharges and the cooler river water to observe how spring discharge and river flow interact throughout the year. The LaDuke study uses a thermal camera on a UAV, river and spring discharge measurements, and precipitation to see how the LaDuke Hot Springs hydrothermal area changes over the course of a year. The research team's interest is in the impact of rain, snowmelt, and river stage on hot spring flow, position, and mixing patterns in the river.

To gather aerial data, they are flying a DJI Matrice 600 Pro UAV over about a half-mile stretch of the Yellowstone River that encompasses the LaDuke hydrothermal area. During flights, both visual and thermal cameras take images every few seconds. The researchers are compiling the resulting mosaic of images to create 3D and temperature maps, allowing them to analyze changes in seep locations, river surface, and temperature.

During each field visit, they use Global Positioning System (GPS) information to locate hydrothermal springs and seeps with centimeter-level accuracy. They also measure Yellowstone River discharge upstream and downstream from the hydrothermal zone. The researchers' ultimate goal is to calculate discharge from the hydrothermal features using a combination of water chemistry, river discharge rates, and temperature data. In addition, they have placed small temperature sensors in steel pipes driven into the riverbed. They will use information from these temperature sensors to determine the vertical velocity of water, which will help them assess whether the groundwater is entering the river or river water is entering the aquifer.

They hope to answer questions like: Do the hot springs and seeps change in time and space? Where does the hot spring water come from? Does the river stage (river water height or elevation) and discharge (high or low flow conditions) affect the hot springs? Preliminary data from the temperature and 3D maps show that some seeps seem to stay at a constant elevation, suggesting there are long-term flow paths that are not affected by the river stage. In some areas there are hot and relatively cold seeps right next to each other.

Quantifying the spatial extent and discharge of hydrothermal features throughout one full year will allow the researchers to look at the seasonality of LaDuke Hot Springs. Determining if increased hydrothermal discharge is correlated with snowmelt or rain events could indicate the hydrothermal feature's susceptibility to climatic patterns, and this may be the topic of further research at other sites.

So far, it is too soon to speculate about what they will see and where research will go. This is the beginning of a study that they hope inspires future research into understanding geothermal and river mixing patterns, and the relationship between hydrothermal features and climate.

This study is partially supported by a grant from the Montana Water Center.