What are Geysers?

Geothermal springs are more commonly known as hot springs. Although there is no set definition, hot springs are often defined as springs where the average water temperature is above body temperature (roughly 37C).

Temperature within the Earth increases with depth, this is caused by processes like nuclear fission and the flexing of the Earth's crust producing friction (and heat) when force is applied by the convection currents of magma in the mantle. The centre of the Earth is estimated to be around 5360C and all this heat has to go somewhere!

Water Circulation in a Geothermal Reservoir:

(Source-http://blogs.kqed.org/climatewatch/files/2010/08/Geothermal_diagram.jpg)

The heat travels outwards and can heat stores of water that are deep underground. Four main types of geothermal feature exist: 

• Geysers
• Hot Springs
• Mudpots
• Fumaroles

A geyser is a type of spring that releases water that has been heated by the Earth's thermal energy. This water builds pressure under the surface in chambers which are informally known as "geyser reservoirs" and then, once the pressure exceeds that of the rock plug sealing the chamber, the superheated column of steam and water bursts out. These spouts often reach high into the air.

Castle Geyser Erupting - Yellowstone National Park:

Geysers are generally aligned along faults; however over half of the worlds 1000 geysers exist in Yellowstone National Park which is a hotspot and, as mentioned in a previous post, a supervolcano. [Link] The plumbing system along faults is made up of a intricate matrix of fractures, fissures, porous rock and sometimes chambers. For a geyser to form and not a hot pool, there must be constrictions in the system so that pressure can build up to create the periodic eruptions.

(Source-http://www.flickr.com/photos/bigskykatie/2424233856/in/set-72157604528569009)

As the water is under so much pressure as it heats under ground, it can be heated to well beyond normal boiling point. This means that when the water is released into the air (at the much lower atmospheric pressure) it expands, and the lower pressure turns the superheated water into steam firing the superheated water and steam high into the air.

Anatomy of a Geyser:

(Source-http://www.sciencebuddies.org/science-fair-projects/project_ideas/Geo_img065.jpg)

Old Faithful, in Yellowstone National Park, is probably the most famous geysers in the world and it erupts roughly every 30 minutes at a height of 60-100 feet. 

Geysers often exist alongside other geothermal features like hot springs, mudpots and fumaroles. Hot springs form when there isn't a constriction in the plumbing which means that pressure cannot build up so the water flows at a fairly steady rate. These are very popular tourist destinations although, personally, the geysers are much more enthralling!

Further Reading:
http://www.waterencyclopedia.com/Ge-Hy/Hot-Springs-and-Geysers.html
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Geo_p040.shtml


A quote to have a think about:

Oceans of thermal water heated in a thousand centres to the boiling point; low, half-molten islands, dim through the log, and scarce more fixed than the waves themselves, that heave and tremble under the impulsions of the igneous agencies; roaring geysers, that ever and anon throw up their intermittent jets of boiling fluid, vapour, and thick steam, from these tremulous lands.

(Hugh Miller - Sketch book of Popular Geology (1859) pg238-9)


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