The Hot Springs of Yellowstone National Park

Audio recording of this lecture

We'll be talking about a wide variety of thermophilic organisms in this course, and many of these were originally isolated from the hot springs of Yellowstone National Park. Today, then, we'll talk about Yellowstone and the general features of hot spring environments, and have a look at some of the specific springs from which many of the organisms we'll be talking about grow.

Yellowstone National Park

Yellowstone National Park ocupies about 6000 square kilometers of the northwest corner of Wyoming, and was established as the world's first national park in 1872. Although YNP is renowned for it's scenery and wildlife (especially bears, which are now scarce in the park), the main attractions are it's geysers, hot springs, and fumaroles. The central region of the park is predominated by a 46 by 77 kilometer caldera (volcanic basin) formed by volcanic eruptions 1.8, 1.2 and 0.6 million years ago (notice the timing - we're due!).

Hot springs, geysers, solfataras, and fumaroles

The geysers and hot springs of YNP are the current manifestations of this volcanic activity. Hot springs occur when cool groundwater percolates down through fractures in the bedrock to the vicinity to the hot magma dome underlying YNP. The water is heated and, because is is now less dense than the surrounding water, rises to the surface in the form of hot springs at or near the boiling point (93C at that altitude).

These springs can take several forms: hot springs, geysers, fumaroles, and solfataras, depending on how fast the water flow is and the shape and size of the outflow plumbing.

	Fumaroles are formed when a hot spring has a high heat flow and low water flow. The water is all converted to high-pressure steam which blasts out of the spring outlet.
	Hot springs are formed when the water flow is higher than the heat flow. The water emerges at high temperatures, but as a liquid. The dissolved minerals often precipitate at the surface as the water cools, forming large stony structures, or creating silica slurries (mud pots).
	A geyser is a hot spring with a large internal water volume below a constriction in the plumbing. The water inside is heated to higher & higher temperatures, until it starts to boil.The steam pushes the overlaying water upward & out of the outflow, which relieves some of the pressure on the water below. This allows more of the water to vaporize, pushing more water out, and so forth - a chain reaction. When enough heat is blown-off in the form of steam for the deeper water to cool, the eruption stops, and the plumbing slowly refills with water & begins the reheating process.
	A solfatara is an area of heated soil. It starts as a small hot spring with low heat and water flows. It is a hot spring that doesn't really make it to the surface, and deposits it's load of heat and dissolved minerals into the soil.

These photographs (except for a couple of professionjal photos, which are a bit pixelated in these scans) were taken over the course of several field expeditions to Yellowstone to collect samples from hot springs. On one of these trips we organized a series of scuba dives in Lake Yellowstone to look for very high temperature underwater outflows - because of the increased pressure, the boiling point of water is higher underwater.

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