By Kevin Krajick
Geologist Carolina Muñoz-Saez is in the business of hydrothermal systems. Her specialty: studying natural plumbing networks that circulate hot water underground, and occasionally erupt above it. These drive the geysers and hot springs of Yellowstone National Park. In other locations, they provide energy for electricity generation or heating. Some host unique microbial life forms. And, under the right conditions, circulating waters may pick up gold, copper or other valuable commodities from surrounding rocks, and concentrate them; many of the world’s most productive mines are the giant dried-up remains of onetime hydrothermal systems.
Muñoz-Saez got her start helping identify potential sites for mining and energy production in her native Chile, and since earning a PhD. at the University of California, Berkeley, she has spent much time investigating the often mysterious doings of geysers. Most recently she coauthored a paper about Yellowstone’s Steamboat Geyser, the world tallest (water and steam shoot up nearly 400 feet), which recently reawakened after a decades-long restless sleep.
Now a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory, she will soon go to the Chilean Andes to explore how geyser activity there may be related to the comings and goings of glaciers over tens of thousands of years. Working with a Lamont-Doherty team specializing in glacial geology, she hopes to help pinpoint the timing of natural climatic forces that have driven past growth and recession of the ice.
I spoke with Muñoz-Saez recently about her work.
Where do hydrothermal systems develop?
Hydrothermal systems form when groundwater is in contact with hot rocks at depth. They’re usually associated with volcanoes or magma bodies that are still cooling down. The water is mostly from precipitation, with the addition of magmatic fluids. Faults can bring the less dense hot fluids to the surface, generating hot springs and geysers. Hydrothermal systems are common in active tectonic plate boundaries and hot spots, both in the continents and on the ocean floor.
How did you get interested in geology, and why did you start specializing in hydrothermal systems?
I grew up in Chile, a country where the earth is active, and extreme geological phenomena like large earthquakes and volcanic eruptions are very common. This motivated me to learn about the different processes generating those impressive events. I specialized in hydrothermal systems because they are dynamic systems that connect different fields: volcanoes, hydrogeology, biology, climate, ore deposits and energy resources.
A lot of this field is driven by the search for minerals or geothermal resources. What have you done in this regard?
Before starting graduate school, I worked in the geothermal and mining industry. Hot fluids from hydrothermal systems can carry and accumulate metals in the shallow subsurface. I’ve worked in the central Andes in Chile, exploring for metals in epithermal deposits, which are fossilized volcanic-hydrothermal systems. Although hydrothermal activity occurs in many regions around the world, geothermal energy is still largely underdeveloped, due the high upfront investment needed. To help overcome the economic barriers, I also worked in a non-profit to explore and quantify the size of geothermal resources in southern Chile, and to promote the direct uses of geothermal energy in rural communities that rely mostly on burning wood.
I get the impression that you are really into geysers. Where do we find them, and what attracts you to them?
Geysers are uncommon—there are only about a thousand reported around the world. Around half are in Yellowstone National Park, and most of the rest are in Chile, Iceland and the Kamchatka Peninsula of Russia. Geysers are fascinating in that they can provide valuable information about past climates, biology and metal deposits. They erupt frequently and also can be used as natural laboratories to understand more complex eruptive systems such as volcanoes. Active geysers have been discovered around the solar system such as in Enceladus, one of Jupiter’s icy moons.
Tell me about your upcoming trip to Chile. How do geysers relate to glaciers, and what might this tell us about climate?
I have been working for several years in a geyser field in the Chilean Altiplano called El Tatio. It’s the largest hydrothermal field in South America. It has deposits of material precipitated out from geyser activity, called sinter, which overlie glacial deposits. Dating these hydrothermal deposits, I found that the hydrothermal activity in the area started in the same time frame that deglaciation from the last glacial maximum occurred in the area, around 27,000 years ago. However, the glacial deposits around El Tatio have not been dated yet. My upcoming trip is to collect samples from the glacial moraines and constrain the age of the deglaciation. Changes in pressure and water supply due to deglaciation could have contributed to the activation of the geyser field.
What have we observed about life forms that inhabit hydrothermal systems, and what might they be able to tell us?
Hydrothermal vents host microbes that are adapted to extreme temperatures and chemical compositions, similar to those conditions on early Earth and other planets. Deposits around hot springs and geysers preserve relics of this past microbial life that can help us understand the origin and evolution of life. Mars rovers and orbital images have identified outcrops comparable to hot-spring deposits on Earth, and these are the main targets for exploring for remains of past life on that planet. Scientists have also found multiple medical and industrial uses from the bacteria living in hot springs. In fact, the PCR test used for detecting COVID-19 uses an enzymatic process found in bacterial mats in Yellowstone.
Are there things about hydrothermal systems that we still really don’t understand?
There are many open questions. I am particularly interested in understanding the evolution of these systems as the different components change—that is, heat, water and permeability of the subsurface. Most hydrothermal systems are fueled by the heat of volcanoes, but how volcanic unrest affects hydrothermal activity and vice-versa is still poorly understood. The permeable zones that fluids move through can evolve over time as minerals precipitate out. Earthquakes are common in areas where there is hydrothermal activity, and this can also change the permeability. These systems are recharged by precipitation, but we still don’t know how climatic changes affect them. If climate does affect them, how would this impact geothermal energy resources? And, what are the time scales on which fluids circulate, and the ages of hydrothermal fluids?