The Science of Hot Springs

Some countries naturally come to mind when you think of natural hot springs and/or geysers.

Japan, Iceland and New Zealand are all small countries which seem to have more than their fair share of hot springs. But why? Having a plethora of thermal water sources might look like a blessing at first glance, but they come with a price, a much higher risk of volcanic and tectonic activity. The three countries mentioned, as well as any other area with a lot of hot springs also has to deal with more earthquakes and volcanoes in return for the benefits of their underground hot water reservoirs.

So just how do geysers and hot springs work? Why does the water come up to the surface instead of staying underground? Most underground water is not in close contact with the molten rock under the earth, but around the boundaries of tectonic plates where volcanoes and earthquakes occur, the heat is much closer to the surface, and hence in close contact with the groundwater.

The contact causes the groundwater to heat up, but because of the underground pressure the boiling point is much higher than normal and the water becomes superheated. Heated water has a natural tendency to rise. As the water rises it starts to lose pressure and then flashes into steam, which propels the water upward with even more force, finally escaping to the surface as a geyser or a hot spring. The only difference between the two is that geysers release water intermittently, while hot springs release water steadily.

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