People may be forgiven for associating geysers with the famous Old
Faithful of Yellowstone National Park in the US, for actually the name
originated in Iceland. Years ago I had to travel there myself to learn
this fact despite having had a good education!
It is from The Great Geysir of Iceland, which first erupted in the
14th century, that the world's geysers take their name. It used to erupt
every 60 minutes until the early 1900s when it became dormant. Earthquakes
in June 2000 subsequently reawakened the giant and it now erupts approximately
every 8 to 10 hours.
second most famous geyser in Iceland is Strokkur, which erupts every
8 minutes throwing a column of water and steam to a height of 20 metres
or so. There are also several other smaller ones.
Geysers are found in active volcanic areas or land that is prone to
earthquakes. Thermal or hot springs are also a feature, as are boiling
mud pools, often appreciated for their medicinal qualities.
The powerhouse of a geyser lies deep underground, where surface water
seeps through fissures and collects in caverns. The temperature of the
surrounding volcanic rock, at around 200 °C, heats the trapped water,
causing it to expand into steam and force its way up and out.
the case of the Great Geysir, the depth of the column through which
the steam rises is approximately 23 metres. The erupting water once
reached a height of 60 metres, but today its maximum is only 10 metres.
On the surface, the mouth of the geyser is circular with what looks
like a little pile of stones around its edge. The area is coated with
a pale mineral crust and the water in the surrounding basin is crystal
clear and near boiling point.
Watching a geyser erupt, even a small one, is a fascinating sight.
First the water starts to boil, then very quickly a bubble forms and
bursts as the steam, hotter and lighter than the boiling water, forces
its way skywards. I made my visit in October one year, and to see steam
evaporate in the air and turn to into ice as touched the ground was
eruptions are particularly fierce one can sometimes feel the earth underfoot
shaking slightly and hear distant rumbles. With the eruption comes a
smell of sulphur, fortunately carried away on the wind!
The regularity of eruption can generally be timed to the minute. This
is probably due to the time it takes for the expelled water to sink
back down into the cavern and reheat to the necessary temperature. As
it is the same amount of water that goes through the cycle, it takes
the same amount of time for each cycle.
To encourage a geyser to erupt earlier than its natural cycle, stones
or even washing-up liquid can be thrown in to break the surface tension
of the water. This can be dangerous, though, as the stones will be thrown
back up at tremendous velocity.
© S.G. Servian 2003