The hydrothermal systems of Yellowstone

There are about 950 geysers in the world and more than 500 are located in Yellowstone. There are 4 other large concentrations of geysers, located in Kamchatka (Russia), Iceland, New Zealand, and Chile.


In Yellowstone, the hot underground chamber of magma is located as close as 3 to 8 miles from the surface. The water from snow and rain leaks through cracks in the ground, to a depth of a few thousand feet, and gets heated. Then, it rises under pressure through the cracks to the surface and produces geysers, hot springs, fumaroles and mudpots. There are more than 10,000 hydrothermal features in Yellowstone.

Geysers, hot springs, fumaroles

A geyser’s underground system of cracks is sometimes called “plumbing.” These cracks get constricted near the surface. The water at the bottom of a geyser’s “plumbing” system gets heated above the boiling point. But the surrounding pressure due to the depth and the enormous weight of the top layers of water don’t allow the hot water to boil. However, the bubbles and expanding steam go up the cracks and lift the water above. As a result the geyser outflows, which reduces the pressure on the whole “plumbing” system and the water close to the surface starts boiling. The steam produced in this process forces water out and an eruption occurs. When the reservoir of water empties the eruption stops.

A fountain geyser
A fountain geyser

There is a fountain type of geyser where the water erupts from the pool and shoots in different directions. Another type is a cone geyser. Cones are formed when the water erupts and leaves a thin layer of siliceous sinter (silicon dioxide, which can be found in glass). This siliceous sinter forms a bulbous rock, called geyserite, and eventually builds up a cone. Knowing the rate of the buildup of siliceous sinter, it is possible to calculate the age of a geyser. In the case of Old Faithful the buildup rate of siliceous sinter is one inch per century.

A cone geyser
A cone geyser



A hot spring’s system of underground cracks is not constricted. The water circulates to the surface and evaporates or outflows to nearby streams. Cooled water, which stays in the pool, sinks down the cracks, is heated, and the process repeats itself.

A hot spring
A hot spring


A fumarole is the hottest hydrothermal feature in Yellowstone. Its plumbing system contains little water. The water from rain and snow, which gets down through cracks, gets evaporated and turns into steam. Steam and gases come out of the vent which looks like a hole in the ground. The temperature of the steam can reach 280 F (138 C).

A fumarole
A fumarole

A mudpot is formed in a depression in the ground filled with water from snow and rain. The water in the mudpot is not connected to the underground water supply, but it gets heated by hot steam, hydrogen sulfide and other gases rising through the ground. Microorganisms use hydrogen sulfide as a source of energy and convert it to sulfuric acid. Sulfuric acid breaks down rocks into clay, which boils and bubbles in mudpots.

A mudpot
A mudpot

It was interesting to learn that the green, orange, yellow and rusty streaks which color hot springs, pools and streams are formed by microorganisms, called thermophiles.  These thermophiles thrive in heat.  They are primitive algae, bacteria, and archaea, which have inhabited our planet for 4 billion years. Thermophiles live in water with a temperature of 167 F (75 C) and higher.

Visitors should stay on boardwalks and designated trails in the areas with hydrothermal features. The crust of the earth is thin and the temperatures of hydrothermal features are scorching hot.

Enjoy and admire these wonders of nature safely.




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