An excellent explanation of why geysers erupt when “tickled” with soap or detergent appeared yesterday on the science blog of the USA Science Engineering Festival [March 12, 2012]. It is the clearest writing about geyser action I have seen in a long time.
You can read about my experience watching the soaping of Lady Knox Geyser on New Zealand’s North Island in 2003 in my nugget Rotorua Hydrothermal Areas of New Zealand. Here’s what happens when you soap (or really, add detergent to) a geyser, as it appears on that science blog:
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.
Reading this led me to explore other posts on the blog, including one about integrating the arts into STEM (science, technology, engineering, and math) education, another subject dear to my heart as a dabbler in scientific subjects. Here’s the link: