How are geysers formed?

If your students embark on a school trip to Iceland, a visit to the epic Strokkur geyser is a must. Since this is an educational trip however, why not help your students get to grips with the formation of geysers before you go? We’ve put together a quick guide to help answer your students’ questions throughout your next Iceland school trip.

How are geysers formed?

Geyser formation

For geysers to form, they need three components: a heat source, a constant water supply and an underground plumbing system. The underground plumbing system is usually made up of a series of fissures in the Earth’s surface, reaching deep underground and connecting it to the geyser’s heat source.

The fissures that make up a geyser in the Earth’s rock often have a mineral lining, sealing the fissures and preventing water from seeping out. These minerals are usually found in volcanic rock, which contains a high concentration of rhyolite.

The majority of geysers pull water from surrounding lakes or rivers. As geysers need a heat source, many of them occur in areas with high levels of geothermal activity. The water is heated by magma situated around 5 kilometres below the Earth’s surface – which is a lot closer than usual. The movement of the tectonic plates also creates a great amount of energy, which can also act as a heat source for the geyser.

Geyser eruption

When all of the above components combine, geysers have the potential to erupt. Here is the process of a geyser eruption:

1. Water moves through the geyser’s plumbing system via a series of fissures in the Earth’s rock. With the water being deep underground, the water at the bottom of the system is under immense pressure from the water above it.

2. The pressure on the water raises its boiling point and allows it to reach incredibly high temperatures. The magma at the base of the geyser heats the water throughout the system, trapping energy in the water and raising its temperature.

3. As the water reaches its boiling point, it starts to become more volatile. This activity forces a relatively small amount of water up the geyser, reducing the amount of pressure on the water remaining underground.

4. The sudden drop in pressure lowers the water’s boiling point and it bursts into steam. The steam rapidly expands to 1,500 times the volume of water and this expansion violently forces both water and steam out the mouth of the geyser, erupting out of the Earth’s surface.

5. These eruptions continue for as long as the water in the geyser remains hot enough to force the water out of the geyser opening. The eruptions will stop either when the system runs out of water or it cools down.