Quick Dips

Taking the Pulse of Geysers

The dynamics of geyser operation is complex and poorly understood, yet can tell us much about the state of geothermal fields and about the behaviour of geysers' bigger erupting cousins, volcanoes.

Researchers at the Physics Department of the University of Auckland have been probing the depths of geysers in an attempt to understand what causes the geysers to erupt, what stops them from erupting, and how to preserve these valuable and spectacular natural resources.

Katherine Luketina, who has just completed her MSc thesis on the dynamics of geyser operation, and her supervisors Ron Keam and Murray Johns have put two geysers under the spotlight and come up with some surprising discoveries.

They have found that boiling occurs in the geyser systems in water which is well below the expected boiling temperature for the depth. The difference between the observed and the expected boiling temperature at a depth of two metres was as much as 3^oC.

Potential explanations, such as local atmospheric pressures, the low bulk density of hot water and the presence of bubbles, were not enough to explain the difference.

One possible cause could be that small parcels of hotter water rise rapidly to a depth at which they can boil, but at which their existence is so transitory that it does not register on the temperature sensor. Or it may be that turbulence in the water brings the pressure momentarily low enough for the water to boil. The researchers hope that continuing work will shed more light on this.

They have had to employ some ingenuity in designing and building specialised monitoring equipment for measuring pressures and temperatures in the geyser water several times a second.

As well as using the most recent technology available, the pressure and temperature sensors required for the job needed to withstand high temperatures, abrasion from the sandpaper-like sinter which lines the inner walls of geysers, and hot alkaline water.

Another interesting discovery they made from developing a quantitative method of studying dye dilution rates in the geyser water was that the two geyser systems were composed of two volumes, fed independently with geothermal water, and with limited convection between them. This has prompted the development of a mathematical model to explain the complicated dilution regime seen in the geysers.

When studying the flow from the mouth of one of the geysers they found a burst of high flow every ten minutes superimposed on a two-minute flow cycle. Long-term data on temperatures, flows and chemical composition of the water may be able to reveal the cause of as-yet unexplained fluctuations in the behaviour of the geysers and other geothermal features in the same areas.

Possible causes could be Earth tides, weather effects such as rainfall and atmospheric pressure changes, the buildup of stress in the Earth which precedes an earthquake, and changes in the amount of steam and hot water drawn from the geothermal system for power, heating, and hot water.

Katherine Luketina, Physics Department, Auckland University