AS Viking long ships approached the coast of Iceland about 1,000 years ago, they saw plumes of dense white smoke ascending to the sky. They called the place "smoke bay" or "Reykjavik", but discovered when they landed that the white columns were not smoke at all, but jets of steam and boiling water. So they called these periodic fountains geysirs, from geysa, an old Norse word meaning "gush".
A geyser erupts, often at very regular intervals, from a hole in the ground which lies at the top of a long channel stretching deep beneath the earth, and which may have many passages and channels leading into it. After one eruption, water seeps slowly back into the narrow tube, and is heated by contact with hot lava. The water at the lowest levels heats first, and as it becomes hotter and hotter it would quickly boil were it not for the great pressure exerted on it by the liquid up above; as it is, it becomes "superheated" - a condition that is most unstable.
Sooner or later, this thermal activity far beneath the ground causes an overflow of water at the surface crater. The resultant drop in pressure allows the superheated water to be transformed explosively into steam, providing the impetus for the upward jet in a process that is not unlike that which occurs when the cap is removed quickly from the overheated radiator of a motor car.
Like seas and sailing ships, geysers are often given individual names. Some have an onomatopoeic resonance like Strokkur, "The Chum", or his fellow Icelander Grothrrmal, who takes his name from the rumbling sound that precedes the eruption of the scalding water. Others, in America, have a rather folksy ring - like "Steamboat" and "Old Faithful"; the latter's name comes - from the popular myth that it erupts like clockwork every 63 minutes, although in fact all geysers are fickle, and even this alleged model of dependability can sleep for extended periods, or erupt as frequently as every half an hour.
But others are even more erratic - like Waimangu, the New Zealand geyser named with the Maori word for "Black Water". In 1904 Waimangu sent an explosive jet of water to a record height of 1,500 feet, the highest gusher ever seen, and then sat silently for years. Then, 80 years ago today, at 6.20 pm on Aoril 1st, 1917, it erupted violently and unexpectedly again, killing four people in the process. Then Waimangu retreated -
Back to the burning fountain whence it came,
A portion of the Eternal.
It has been dormant since -
seething, perhaps, and watching, waiting!