BJJ News
D. Jones
recreation and travel
The ‘Blue Bubble’ David Jones reports on a unique phenomenon during a recent visit to Iceland
Fig. 1 The Great Geyser which erupts infrequently and unpredictably
wife and I have just returned from a ‘one-of f ’ voyage which included the Faroe Islands, an eclipse of the sun in mid-Atlantic, the Northern lights and a circumnavigation of Iceland, the volcanic landscape of which was stunning, albeit chilly in March. Among others, Iceland has given us Viking sagas, Björk the mega pop star and Eyjafjallajökull, the volcano whose eruption in 2010 tested newsreaders worldwide and blocked air travel across Europe. The country has also given us the word ‘Geysir’, from the area of that name, which contains a unique combination of geo-thermal activity. Hot springs come in all shapes and sizes, from steaming, sulphurous emissions through boiling surface pools to eruptive geysers which can throw a column of steam and water high into the air. All hot spring activity results from surface water draining through the ground until it meets rock heated by magma. The geothermally heated water returns to the
My
Fig. 2 Little Geysir, a natural hot spring, bubbles contentedly but not a true geyser.
surface by convection through porous and fractured rock. Unlike non-eruptive hot springs, a geyser differs in its subterranean structure which comprises an underground reservoir of water connected to a relatively narrow vent at the surface by one or more thin tubes. As the geyser fills, the water at the top of the vent cools off, but because of the narrowness of the channel, it cannot cool the water below but presses down on it, like the lid of a pressure cooker, thus allowing the water in the reservoir to become superheated, whereby it remains liquid at temperatures well above boiling point. However, when temperatures near the bottom of the geyser rise to a point where boiling begins, steam bubbles rise to the top of the column. As they burst through the geyser’s vent, water overflows and reduces the weight of the column and pressure on the water underneath. With this release of pressure, the superheated water undergoes a process where it instantaneously flashes into steam, creating a violent froth of expanding steam and hot water
which erupts from the geyser. Much of the water falls back to the geyser, the reservoir begins to fill again and the whole cycle is repeated. Unsurprisingly, geysers are relatively rare. Throughout the world - be it in Yellowstone, Rotorua, Iceland or more inaccessible areas of Russia or Chile geysers are a powerful attraction to scientists and tourists alike. The duration of, and time between, eruptions varies greatly from geyser to geyser as a trip to Google will confirm, and it is easy to understand how an enthusiast with a scientific bent might get hooked into the minutiae of the world of geysers. I have no intention of becoming an expert on geysers and boring the pants off anyone who might be weakened into listening to my new-found knowledge of different eruptions around the world. However, our visit to Geysir allowed us to observe a range of geothermal activity and to witness the star of the show, namely the Strokkur geyser, which erupts obligingly every ten minutes or so. The eruption lasts only a few seconds but
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