Old Faithful in action at Yellowstone National Park.
AS a callow youth, I often referred to old men as ‘geezers’! Little did I know then that I would be lecturing about a natural phenomenon with the same pronunciation – geysers – erupting hot springs!
Geysers, not surprisingly, are found in Iceland where the word was derived from the Icelandic ‘geysha’ meaning to gush. Iceland is one of the most active volcanic regions in the world and is ‘rifting apart’ at the rate of two centimetres a year with the western half of this island on the North American Plate and the eastern half on the Eurasian Plate.
At this zone of plate divergence, magma from deep below wells up to form volcanoes, lava flows, hot mud pools and geysers. This island has been described by Canadian professor Edward Chamberlin in his recent book, ‘Islands – how islands transform the world’ as “a land of terrible beauty”.
What is a geyser?
Certainly they are the most impressive water spout displays of geothermal energy and are regularly seen performing in other volcanic regions in the North Island of New Zealand and in Yellowstone National Park, Wyoming, USA. Rainwater and snow melt percolates through the rock fissures below and then interacts with the deep-seated hot magma. The water at such a depth reaches above surface boiling point but, because of the pressure at such depth, it does not actually boil. Instead, it becomes superheated and pressurised.
When the pressure builds up, the superheated water bursts out of the ground in an explosive steam eruption with a noise not dissimilar to that of a passing freight train. A whistling kettle works on the same principle.
Self-perpetuation seems to be a trademark of all geysers once the initial breakout onto the surface occurs. After the first eruption of hot water, pressure on the superheated groundwater is reduced and water becomes steam, which rises through the rock fissures forcing out any overlying hot water. This sequence of events is on-going as more surface water drains downwards, heats up, and the build-up of pressure returns.
Self-made plumbing system
A material called geyserite or siliceous sinter, composed of silicon dioxide (Si O2), is found in the rocks surrounding a geyser and is dissolved from rhyolitic volcanic rocks and deposited on the walls of the natural pipes of a geyser’s plumbing system as well as on the surface, as an evaporite deposit. These deposits strengthen the piping system thus permitting the steam pressure to be maintained right up to the surface.
In Iceland, the power of some geysers has been reduced through man’s tapping the geothermal energy and using the hot water to provide central heating in houses. Thus, a combination of factors, water, geothermal heat, and the right plumbing conditions need to be in place for a geyser to continually erupt.
The Mount St Helen’s supervolcano eruption. – United States Geological Survey photo
Yellowstone National Park
The first of America’s National Parks, which was established in 1872 in Wyoming State, holds half of the world’s geothermal features with over 10,000 recorded examples and 300 geysers or two thirds of all geysers in the world. The whole park is located in a massive caldera, the remnants of a supervolcano that last erupted 634,000 years ago.
Today the landscape exhibits active geyser cones, the most famous of which is undoubtedly Old Faithful. Guide books promise the readers an eruption of water and steam from Old Faithful at regular 80 minute intervals with an ejection of steam and hot water up to a height of 61 metres. Much actually depends on the power of preceding eruptions and the time it takes for the steam pressure to build up to a critical level.
To date, Old Faithful lives up to its name as it only disappoints impatient on-lookers. One geyser, Steamboat, has not erupted for many a year but is known in historic times to blast water and steam 120 metres plus skyward.
Lurking beneath the surface?
I well remember a lesson I taught on vulcanicity on Oct 17, 1989 with reference to earthquakes. I gave a detailed account of the disastrous 1906 San Francisco earthquake. I mentioned that the US Geological Department predicted another major earthquake in the vicinity of the San Andreas Fault soon. “How soon, Sir?” was one student’s immediate response. My reply was simply, “In geological time, maybe tens of thousands of years; in historical time perhaps centuries, decades, years, months, weeks or even tonight or tomorrow! I am not a soothsayer!” That very day, at 5.04pm local time, San Francisco severely shook, with another earthquake and again with extensive damage. The look on my students’ faces next day had to be seen to be believed and I was plagued with such questions as, “How did you know?”
Early last month, the New York Times reported on extensive research by geologists at Arizona State University on fossilised volcanic ash emitted from the last Yellowstone supervolcano eruption. Beneath the national park there lies a massive magma chamber. The research team also analysed crystals in rock debris from this eruption.
These crystals contained fossilised evidence of changes in temperature, pressure, and water content in their original magma chamber location and suggested, together with more recent geothermal activity, that another supervolcanic eruption could take place sooner than was formally thought and perhaps in the near future.
Judging by the amount of magma stored underground in the massive magma reservoir such a supervolcanic explosion would be more than 2,500 times that of the supervolcano Mount St Helens, in Washington State, in 1980, which killed 57 people. Moreover, such an eruption at Yellowstone could blanket most of the USA with a thick layer of ash and plunge the Earth into a ‘volcanic winter’ as incoming solar radiation would be blocked out by plumes of volcanic ash. The human and economic consequences of such an event are too numerous to enumerate.
Up until now, it was thought that supervolcanic eruptions would take centuries for magma reservoir pressures to build up. Certainly, this research suggests a shorter time scale. By studying the rate and frequency of the timings of geyser emissions we, too, may learn more about the underworld of the Roman god of fire Vulcan.
For more read ‘Island – How islands transform the world’ by J Edward Chamberlin (2013) published by Elliott and Thompson Ltd London.