Geysers
This image indicates active geyser distribution around the world.
What are geysers? Where can we find them? Why do they exist and how do they work? This page will concentrate on the mechanics that operate geyser activity and on the different types of eruptions rather than on the aesthetics of the surrounding pools.
A geyser consists of hot water and steam erupting repeatedly from a vent in the ground. Geysers are very rare natural phenomena - there are only about 1000 geysers in the World, a third of which are located in Yellowstone National Park, WY, US. This is due to the fact that in order for a geyser to exist, several specific parameters have to be reunited. The map shows the distribution of geysers around the world.
A geyser consists of hot water and steam erupting repeatedly from a vent in the ground. Geysers are very rare natural phenomena - there are only about 1000 geysers in the World, a third of which are located in Yellowstone National Park, WY, US. This is due to the fact that in order for a geyser to exist, several specific parameters have to be reunited. The map shows the distribution of geysers around the world.
Where to find geysers
Multiple studies carried out at geyser fields around the world show that there are three main factors that are crucial to the existence of a geyser: a water supply, a heat source and a network of underground reservoirs and cracks.
1) Water supply: Where there is a geyser we can be sure to find vast reservoirs of groundwater that nourish the fountain. This reservoir is being constantly renewed by precipitation. Water in the geysers has been dated by the tritium method (tritium/helium ratio) to be around 500 years old. This is the time it takes for it to make its way from the groundwater reservoir to the surface of the Earth in form of a geyser.
2) Heat source: Beneath every geyser is a colourless layer of very hot rock. In fact, most geysers are found in volcanic regions, where hot magma rises from deep within the earth and accumulates in pools near the surface. Some geysers are situated above a plate boundary and others above hot spots, the latter is the case for Yellowstone National Park, where geysers are the most abundant. In the case of Iceland, both are true.
3) Underground network: This is where the distinction between a hot spring and a geyser is made. Hot springs are essentially pools of constantly hot water that rise to the surface in a regular non-violent manner. The eruption of a geyser is permitted by a complex network of cracks and reservoirs that store the water from a reservoir underground before it is spewed to the surface in a violent eruption. In order for it to be efficient, the walls of the network have to be water and air proof. Rhyolite, an impermeable silicate rock usually lines the walls of the conduit.
1) Water supply: Where there is a geyser we can be sure to find vast reservoirs of groundwater that nourish the fountain. This reservoir is being constantly renewed by precipitation. Water in the geysers has been dated by the tritium method (tritium/helium ratio) to be around 500 years old. This is the time it takes for it to make its way from the groundwater reservoir to the surface of the Earth in form of a geyser.
2) Heat source: Beneath every geyser is a colourless layer of very hot rock. In fact, most geysers are found in volcanic regions, where hot magma rises from deep within the earth and accumulates in pools near the surface. Some geysers are situated above a plate boundary and others above hot spots, the latter is the case for Yellowstone National Park, where geysers are the most abundant. In the case of Iceland, both are true.
3) Underground network: This is where the distinction between a hot spring and a geyser is made. Hot springs are essentially pools of constantly hot water that rise to the surface in a regular non-violent manner. The eruption of a geyser is permitted by a complex network of cracks and reservoirs that store the water from a reservoir underground before it is spewed to the surface in a violent eruption. In order for it to be efficient, the walls of the network have to be water and air proof. Rhyolite, an impermeable silicate rock usually lines the walls of the conduit.
How does a geyser work?
The key to understanding how our dynamic planet makes a geyser operate is in the interactions between the three factors outlined above.
The violent explosion of water and steam has its origin in a thermodynamic disequilibrium inside the underground network. Small amounts of water from deep within the mantle rise through the layer of hot rocks, where it is heated to very high temperatures by natural processes (pressure). At the same time, groundwater slowly works its way down through cracks or porous rocks. The upward moving hot water and the downward moving cool groundwater eventually start mixing in the underground reservoirs. Due to the increased pressure at depth, the boiling point of water increases, the hot water that finds its way to the geyser reservoirs is therefore several degrees above the normal boiling point of 100°C and thus some of the water turns into vapour. The vapour rises up and condenses again as it meets the cool groundwater. As the geyser conduit fills (mainly with groundwater), the upper water is gradually heated by the condensation of the vapour and also due to the fact that cooler water is heavier and therefore sinks to the bottom, where it is heated by the hot water moving up from deep within the earth.
Eventually the water in the conduit reaches a temperature that is well above 100°C, the boiling point of water at 1 atm (atmospheric pressure). However, due to the pressure of the overlying water, it cannot leave the conduit by evaporation and the pressure keeps building up. At this point the temperature of the upper water is high enough for the rising steam bubbles to arrive at the top of the network without condensing. After a certain time, this varies from geyser to geyser depending on the nature of the conduit and the heat of the surrounding rocks, there are too many steam bubbles and they end up “clogging” the conduit where it narrows or bends. The bubbles then have to squeeze their way through, squirting out some water as they go.
This is where a chain reaction starts; with some of the water being released, the pressure in the conduit decreases and the overheated water inside is brought to a vigorous boil. The pressured, frustrated water is released at the surface in an eruption of extremely hot water and steam. This once more lowers the pressure inside the conduit again and therefore fuels the boiling. This cycle continues until all the water from the conduit is either emptied or becomes too cool to rise to the surface.
Geysers work in cycles – as soon as the conduit is emptied by an eruption, it starts to fill again and the whole processes repeats. The intervals between two consecutive eruptions range from minutes to years. The Old Faithful at Yellowstone National Park, WY, US – the most famous geyser – erupts roughly every 90 minutes and ejects particles up to 184 meter high. However, some geysers erupt very irregularly, like the The Great Geysir in Iceland, which after having been dormant, now erupts monthly only – if at all.
The violent explosion of water and steam has its origin in a thermodynamic disequilibrium inside the underground network. Small amounts of water from deep within the mantle rise through the layer of hot rocks, where it is heated to very high temperatures by natural processes (pressure). At the same time, groundwater slowly works its way down through cracks or porous rocks. The upward moving hot water and the downward moving cool groundwater eventually start mixing in the underground reservoirs. Due to the increased pressure at depth, the boiling point of water increases, the hot water that finds its way to the geyser reservoirs is therefore several degrees above the normal boiling point of 100°C and thus some of the water turns into vapour. The vapour rises up and condenses again as it meets the cool groundwater. As the geyser conduit fills (mainly with groundwater), the upper water is gradually heated by the condensation of the vapour and also due to the fact that cooler water is heavier and therefore sinks to the bottom, where it is heated by the hot water moving up from deep within the earth.
Eventually the water in the conduit reaches a temperature that is well above 100°C, the boiling point of water at 1 atm (atmospheric pressure). However, due to the pressure of the overlying water, it cannot leave the conduit by evaporation and the pressure keeps building up. At this point the temperature of the upper water is high enough for the rising steam bubbles to arrive at the top of the network without condensing. After a certain time, this varies from geyser to geyser depending on the nature of the conduit and the heat of the surrounding rocks, there are too many steam bubbles and they end up “clogging” the conduit where it narrows or bends. The bubbles then have to squeeze their way through, squirting out some water as they go.
This is where a chain reaction starts; with some of the water being released, the pressure in the conduit decreases and the overheated water inside is brought to a vigorous boil. The pressured, frustrated water is released at the surface in an eruption of extremely hot water and steam. This once more lowers the pressure inside the conduit again and therefore fuels the boiling. This cycle continues until all the water from the conduit is either emptied or becomes too cool to rise to the surface.
Geysers work in cycles – as soon as the conduit is emptied by an eruption, it starts to fill again and the whole processes repeats. The intervals between two consecutive eruptions range from minutes to years. The Old Faithful at Yellowstone National Park, WY, US – the most famous geyser – erupts roughly every 90 minutes and ejects particles up to 184 meter high. However, some geysers erupt very irregularly, like the The Great Geysir in Iceland, which after having been dormant, now erupts monthly only – if at all.
What makes every geyser so unique?
Until now we have talked about the global mechanisms of geysers, but if we observe geysers around the world or even within the same geyser field, we see that they do not behave exactly the same way. Some geysers have particularly violent eruptions, others last for relatively long periods of time, some are unusually cool....Two main factors that influence the behaviors of individual geysers are: the shape of the conduit and the gas content.
Factors influencing geyser behaviour
Figure 2 shows different types of geyser conduits.
1) The shape of the conduit: There are two main types of geysers: columnar and fountain.
Columnar geysers such as the Old Faithful of Yellowstone erupt in fairly straight columns that shoot several tens or even hundreds of meters up. This is due to a pipe-like underground reservoir that (Figure 2, A and B) mirrors the shape of the column that comes out at the surface. The intensity and the duration of the eruption varies with the width of the pipe. The Old Faithful has a Figure 2.A type conduit and its eruptions are long and high. The Round Geyser, also from Yellowstone, has a Figure 2.B type conduit and its eruptions are short, violent and do not rise as high.
Fountain geysers, also called pool geysers, erupt in a more spacious manner and are characterised by being surrounded by pools of hot water. The underground structure of fountain geysers is very different from that of columnar geysers. Some have a system of pools connected by narrow pipes (Figure 2.D), during eruption the pools empty repeatedly and we see successive eruptive waves. Other types of fountain underground networks include type Figure 2.E conduits which have one big isolated pool and type Figure 2.F conduits – needle-like canals. Geysers belonging to the last two systems have long and mild eruptions. All of the fountain geysers have a much wider opening at the surface, than the columnar geysers.
2) Gas Content: Some Geysers have an unusually high content of volcanic gases such as CO2. High gas content lowers the boiling point of water well below 100°C. Therefore a geyser with a high gas content can erupt even if its heat source is not powerful enough. The gas becomes the driving force of the eruption. The resulting geyser then looks like it spits out very hot water and steam that accumulates in pools where the water continues to boil, but in fact the water is below 100°C. This type of geyser is common in areas with oil and gas reservoirs.
Other circumstances like rainfall quantities and tides of the Earth can also influence the behaviour of geysers to a certain degree. In these cases it is mainly the frequency of eruptions that is altered. High tides and larger amounts of rainfall tend to shorten the intervals between consecutive eruptions, and low tides and periods of lesser rainfall tend to stretch those intervals.
Columnar geysers such as the Old Faithful of Yellowstone erupt in fairly straight columns that shoot several tens or even hundreds of meters up. This is due to a pipe-like underground reservoir that (Figure 2, A and B) mirrors the shape of the column that comes out at the surface. The intensity and the duration of the eruption varies with the width of the pipe. The Old Faithful has a Figure 2.A type conduit and its eruptions are long and high. The Round Geyser, also from Yellowstone, has a Figure 2.B type conduit and its eruptions are short, violent and do not rise as high.
Fountain geysers, also called pool geysers, erupt in a more spacious manner and are characterised by being surrounded by pools of hot water. The underground structure of fountain geysers is very different from that of columnar geysers. Some have a system of pools connected by narrow pipes (Figure 2.D), during eruption the pools empty repeatedly and we see successive eruptive waves. Other types of fountain underground networks include type Figure 2.E conduits which have one big isolated pool and type Figure 2.F conduits – needle-like canals. Geysers belonging to the last two systems have long and mild eruptions. All of the fountain geysers have a much wider opening at the surface, than the columnar geysers.
2) Gas Content: Some Geysers have an unusually high content of volcanic gases such as CO2. High gas content lowers the boiling point of water well below 100°C. Therefore a geyser with a high gas content can erupt even if its heat source is not powerful enough. The gas becomes the driving force of the eruption. The resulting geyser then looks like it spits out very hot water and steam that accumulates in pools where the water continues to boil, but in fact the water is below 100°C. This type of geyser is common in areas with oil and gas reservoirs.
Other circumstances like rainfall quantities and tides of the Earth can also influence the behaviour of geysers to a certain degree. In these cases it is mainly the frequency of eruptions that is altered. High tides and larger amounts of rainfall tend to shorten the intervals between consecutive eruptions, and low tides and periods of lesser rainfall tend to stretch those intervals.