The North Carolina Zoo’s newest exhibit doesn’t house mammals or reptiles or amphibians or even exotic plants – but geysers, five of them, to be exact. Although these new features are manmade, they erupt with the same grace and beauty as their natural-phenomenon counterparts.

In nature, geysers are vents in the Earth’s surface where pressure builds and periodically ejects columns of hot water and steam into the air. At the zoo, the idea was to tie-in the exhibit’s animals – elk and bison – with the geographic area of Wyoming and Yellowstone National Park, where geysers are normally found. At the zoo, it’s an enrichment experience for visitors, who can feel the spray and sense the excitement of the eruption. No worry, though. At ambient air temperature, these are considerably cooler than the boiling hot-water eruptions of natural geysers.

“Old Faithful” geyser in Yellowstone National Park in Wyoming is probably the world’s best known geyser, erupting every 60 to 90 minutes and blasting thousands of gallons of boiling hot water 100 to 200 feet into the air.

At the zoo, visitors can experience five geysers with varying spouts (the highest being about 15 feet) but at considerably cooler temperatures.

Despite the unbelievable forces that drive geyser eruptions, they are among the earth’s rarest and most fragile natural phenomena. Factors such as earthquakes and landslides can alter a geyser’s eruptions or destroy it altogether.

Worldwide, there are thought to be only about 1,000 geysers, and most of those are located in Yellowstone. All known geysers occur in just five countries: 1) the United States, 2) Russia, 3) Chile, 4) New Zealand and 5) Iceland. But scientists have spotted a geyser-like eruption on Jupiter’s moon. All the earth’s eruptions occur where there is geologically recent volcanic activity and a source of hot rock below the surface.

The process begins as water migrates down to the geyser’s plumbing system through fissures, or openings, in the ground. Miles deep, the water at the bottom of this giant plumbing system is under incredible pressure from the water above it. The geyser system is much like a giant pressure cooker.

In simplest terms, a natural geyser is a special type of hot spring or other hydrothermal activity that builds up pressure underground and erupts periodically. Groundwater circulating under the earth’s surface becomes heated by the hot rock below and moves toward the surface through geyser tubes or channels. As the heated water rises, it follows these channels leading upward. The underground water becomes progressively hotter, but it will not vaporize in the geyser channels because of the greatly increased pressure exerted by the weight of the overlying water.

Finally, the steam expands as it nears the top of the water column. At a critical point, the steam bubbles actually lift the water above, causing the geyser to overflow. Then system pressure decreases, resulting in violent boiling at the surface.

Eruptions continue as long as the geyser’s water remains hot enough to push water out of the geyser opening. Eventually, either the water will cool down enough for the eruption to stop or the system will run out of water. Then the cycle starts again.

While most geysers erupt through this superheated water system, there are also cold-water geysers that are driven by carbon dioxide-rich water trapped beneath the earth’s surface.

When the built-up pressure in a cold-water geyser decreases, the carbon dioxide bubbles in the water expand, pushing water out as an eruption.

The zoo’s geysers are another example of how the park has tried to immerse visitors in the exhibits to enrich their experience. Conceived more than a year ago, the exhibit took five months to build, with the zoo’s design staff doing the majority of the construction – except the “plumbing.” Zoo visitors can daily view “eruptions” at the third overlook in the North America region.



Tom Gillespie lives in Trinity and is a journalist and public affairs specialist at the North Carolina Zoo. For more information on the zoo’s plant and animal collections, special events and education programs, go to their Web site at www.nczoo.org