Feeling perturbed: Seasonal disturbances of Yellowstone's hydrothermal systems

Release Date:

Yellowstone National Park's Norris Geyser Basin is a hydrothermal basin full of geysers and thermal pools that are constantly changing.

Factors like air temperature, amount of snow and rain, depth of the groundwater table, and the influx of magmatic fluids perturb an already dynamic hydrothermal system. The interaction of these factors with the constantly evolving hydrothermal system is a complex scientific puzzle that sometimes goes a little haywire. We call these quasi-annual events "seasonal disturbances," or just "disturbances" for short, and there may be one occurring right now.

This is a comparison of before and after Norris Seasonal Disturbance.

Norris Back Basin features with usually cloudy water have turned muddy and turbid, as is shown by the transitions from the left to right in the two pictured thermal pools. In the case of the second pool, the transition between cloudy to muddy also saw the thermal feature boil away in between the transition.

(Public domain.)

The last major documented disturbance in Norris Geyser Basin took place in the summer and fall of 2003 (smaller ones occur almost every year). During that disturbance, the water chemistry of hot pools changed, the turbidity and cloudiness of normally clear features increased, and the temperatures of many geysers and thermal pools in the area increased. Scientists proposed that the cause of this disturbance was the interaction between an abnormally low groundwater table and the hydrothermal features, an occurrence that has been hypothesized to occur during the drier late summer months when the level of the water table falls. This results in a large-scale "boiling" of the subterranean hydrothermal system, and a "disturbance" at the surface.

Interestingly, Norris Geyser Basin may currently be experiencing a different type of seasonal disturbance. To date, Norris Basin's Steamboat Geyser, world's largest active geyser, has erupted 10 times with no obvious predictability in precursory signs. Furthermore, the interval between Steamboat Geyser eruptions, the length of the water fountain phase of the eruption, and the length of steam eruption phase have also not been predictable. The latest set of repeated Steamboat eruptions, which began on March 15, 2018, ensued approximately 16 days after an increase in average daily air temperature and roughly 20 days after a nearby stream gauge recorded a seasonal springtime increase in discharge.

This is a example of a Norris Steam Valve disturbance.

This feature is shown in 1998 during calm, stable conditions (top), before the 2018 disturbance when it was an ephemerally filled fumarole (middle), and during the 2018 disturbance when it was a muddy pool with rare geyser eruptions up to 8 feet tall (bottom).

(Public domain.)

Although previous seasonal disturbances have been linked with drier, late summer arid conditions, the current disturbance seems to be associated with unusually wet climatic conditions. The winter of 2017-2018 recorded high snowpack in Yellowstone National Park clocking in at roughly 240-360 inches of snow (normal average snowpack is less than 240 inches). Also, climate studies in Yellowstone over the last 40 years show that snow is now melting earlier in the year, contributing an earlier influx of water to hydrothermal systems like the Norris Geyser Basin. Finally, so far this year precipitation is 125-150% of the average amount over the last 30 years in the Norris Geyser Basin area.

Could this seasonal excess of water percolating into the Norris hydrothermal system cause more frequent geyser eruptions, and the "filling" of several thermal features in Norris Back Basin? It's an interesting question that bears more investigation. National Park Service geologists have observed changes in Norris Back Basin thermal pools during and after the winter storm of June 15-18, 2018 such as rare geyser activity in features that do not regularly erupt and increased turbidity in many hot pools. Continued monitoring of the pH and temperature of Norris thermal features may lend more insight into what is currently happening at Norris Geyser Basin in these wetter-than-normal conditions.

Although the ultimate cause of seasonal disturbances in volcanic hydrothermal systems such as Norris Geyser Basin are still largely unknown, it is fascinating to observe a disturbance triggered by different external conditions than previous seasonal disturbances—a fact that dramatically highlights the dynamic complexity of interaction between Yellowstone's hydrothermal system, climate, hydrology, and geology.