It's confirmed now - Mother Earth is a blue eyed girl!
You see the center pond and main vent on the Geysir itself, as its steaming watery eye silently stares towards the sky, in the dead of night at 01:03 AM.
This is the oldest hot spring known in the world, residing in Haukadalur, Reykholt, southern Iceland. It's first mentioned in writing in the year 1294,
when a series of earthquakes first triggered it off. The Icelandic word geysir was later established as a term used world-wide for this phenomenon.
Today it is almost dormant, just one or two half-hearted blows a day, to max 10m/30ft height. At it's peak it shot up to 60m/200ft in the air!

The mechanisms triggering the Geysir are like this (source http://www.geysircenter.is/english/geysir/geolog.html ):
Geysirs erupt because the thermal water ascending through their channels boils at some depth below the surface. As the water boils it flashes into steam,
and as steam occupies far greater volume than water, the water above in the channel is thrown high up into the air. At about 23m/75ft depth in the Geysir pipe the
water is at 120°C/248ºF temperature. It is in equilibrium with the pressure of the water column above in the pipe, i.e. the weight of the water above keeps the boiling down.
At a depth of around 16m/52ft, the temperature of the water sometimes rises above boiling, seen as increased turbulence at the surface. This turbulence (boiling)
can increase to the point where the water above in the pipe is lifted slightly, and a chain reaction starts - the pressure decreases making further boiling possible
and the water flashes into steam, resulting in an eruption in Geysir. The boiling now extends also down into the pipe, throwing more water into the air.
When all the water in the pipe has been thrown away, the water coming from depth changes immediately into steam and a steam eruption follows the water eruption,
with accompanying noise. The water-phase lasts for a few minutes and the steam-phase considerably longer, gradually dying out before the cycle starts again.
As the steam-phase dies out the water has drained the channels deep into the earth, and it will take 8-10 hours for Geysir to regain its water.

Following large earthquakes in southern Iceland on June 17th and 21st 2000, Geysir started to erupt after having been mostly dormant since 1915.
It woke up again for a period from 1935 though, and erupted then for several years, but then got back to sleep. Now it erupts every day, sometimes several times per day,
but has not regained its former glory, when the eruptions got up to 50-60m/160-200ft. Now it erupts a mere 8-10m/26-30ft, but does it just intermittently
for some time when it starts. The eruptions start as turbulence at the surface, then gushes of water are thrown 8-10m/26-30ft into the air.
As the erupting water falls back into the bowl, it cools the water in the bowl and the boiling stops. The adjacent geyser Strokkur (churn) erupts every 8 minutes
and has been the main geysir in the area since 1963, when its channel was thoroughly cleaned. Strokkur was formed in an earthquake in 1789
and was active until the next earthquake in 1896, which shut the geysir down.