Geyser Gets a Little Help From Chemistry

By Joe Schwarcz PhD, Author, USASEF Expo Performer, AT&T Sponsored Nifty Fifty Program Speaker

Yellowstone National Park's iconic "Old Faithful" geyser is pretty faithful. It can be counted on to erupt every 50-90 minutes. Iceland's "Great Geysir," from which all other geysers get their name is less reliable. It was mostly dormant for sixty five years before it began semi-regular eruptions again in 2000 thanks to an earthquake. But in New Zealand, you can set your watch by the eruption of the Lady Knox Geyser, named after a former Governor of the country. At exactly 10:15 AM every day a spectacular plume of water and steam bursts into the air to a height of up to twenty meters. How can a natural phenomenon be so predictable? Well, in this case nature gets a little help from chemistry.

At the appointed time, a detergent solution is poured down the channel from which the water erupts. This has the effect of reducing the surface tension of the water that deep within the shaft has been heating up to boiling temperatures due to underground volcanic activity. Surface tension refers to the attractive force between water molecules, and is in fact responsible for water being a liquid at ordinary temperatures. Liquids are characterized by the close proximity of their component molecules, while in gases the distance between molecules is much greater. If the surface tension of a liquid is decreased, the H2O molecules can separate from each other with greater ease, with the result that the liquid turns into a gas. Molecules of "surfactants," a class of substances that encompasses soaps and detergents, wiggle their way in-between water molecules, allowing the boiling liquid to instantly turn into steam. The steam then forces the water that has collected in the channel to burst upwards, and we have an eruption.

The possibility of making a geyser erupt artificially was discovered by accident in New Zealand in 1901 when an "open prison" was established at Waiotapu for criminals who were deemed not to be a danger to society. It so happens that this is one of the most volcanically active areas of the world and the prisoners took advantage of the hot water seeping up from the natural thermal springs to wash their clothes. One day one of them must have used just the right amount of soap and triggered an eruption when the soap solution found its way down the fissures in the rock into the chambers in which underground water had pooled. This is the concept used today to stimulate eruption of the Lady Knox Geyser although detergents have replaced soap because they have been found to be less damaging to the geyser's internal natural plumbing. On occasion Iceland's Great Geysir has also been "soaped" but this is now prohibited for environmental concerns.

Long before the prisoners made their accidental discovery, the science of geyser eruptions had been worked out by none other than Robert Bunsen, of burner fame. Actually Bunsen did not invent the famous burner but did improve upon existing equipment by showing that mixing the combustible gas with just the right amount of air led to a high temperature non-luminous flame. Such a flame was very useful in the development of Bunsen's most famous discovery, the spectroscope. In collaboration with physicist Gustav Kirchoff, Bunsen designed an instrument that would pass the light emitted from a sample heated by his burner through a prism. The "spectrum" of light produced was found to be characteristic of the element found in the sample. Before long Kirchoff and Bunsen had identified cesium and rubidium as new elements and paved the way to the identification of thallium, indium, gallium, scandium by others through spectroscopy.

In 1845, during his tenure as Professor of chemistry at Marsburg University, Bunsen was invited by the Danish government on a geological trip to Iceland following the eruption of Mount Hekla. Bunsen had a lifelong interest in geology and used the occasion to study the gases released from volcanoes and performed analyses on volcanic rocks. He also became interested in Iceland's abundant geysers, especially "The Great Geysir" that propelled water to a height of some fifty meters. Bunsen hypothesized that eruption occurred when a column of underground water was heated around its middle by volcanic activity. In the true spirit of science, Bunsen constructed an artificial geyser in the laboratory consisting of a basin of water from which a long tube filled with water extended upwards. He heated the tube at various points and showed that it was when the water in the middle reached its boiling point that an eruption occurred just like in a natural geyser.

Geysers can do more than excite tourists. In Iceland hot water from geysers is used to heat homes and warm greenhouses, allowing food to be grown in an otherwise inhospitable climate. The accumulation of steam deep within the ground that makes geysers possible can also be tapped by geothermal power plants to produce electricity. Geothermal energy is a great source of electricity but drawing off the steam can lead to the destruction of geyser activity.

Not all geysers gush steam and hot water. In the case of cold-water geysers the eruptions are driven by carbon dioxide gas that forms as limestone, calcium carbonate, decomposes. The gas becomes trapped in underground aquifers until it builds up enough pressure to explode towards the surface through cracks in the strata propelling water into the air. Some of the gas remains in the water in the form of small bubbles so that the geyser actually dispenses soda water.

If you want to experience a mini-cold-water geyser, just drop a couple of Mentos into a bottle of Diet Coke. But do it outside. It makes a mess. If you use a special tube (available from Steve Spangler Science) that can simultaneously drop 7-10 Mentos into the bottle, you'll be treated to a true spectacle as the liquid bursts to the stunning height of about ten meters. That's still some 490 meters short of the super eruptions once produced by the Waimangu Geyser in New Zealand between 1900 and 1904 before the natural plumbing was destroyed by a landslide. The world's tallest geyser now is Yellowstone's Steamboat Geyser that propels water some ninety meters into the air. Unfortunately its eruptions are not predictable. Except on YouTube.