Sciences Secondary volcanic activities: Geothermal springs, Geysers and Fumaroles Geothermal Springs A geothermal (or hydrothermal) spring is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal springs in many locations all over the crust of the earth. Geothermal Springs Surface water percolates downward through the rocks below the Earth's surface to high-temperature regions surrounding a magma chamber, either active or recently solidified but still hot. When the water is heated, becomes less dense, and rises Surface water back to the surface along fissures and cracks. Sometimes these features are called "dying volcanoes" because they seem to represent the last stage of volcanic activity as the magma, in depth, cools and hardens. Water percolation Heated water rises up The temperature of hot springs depends on factors such as: •the rate at which water circulates through the underground channels Hot rocks •the amount of heat at depth •the dilution of the heated water by cool ground water near the surface. Geothermal Springs The water issuing from a hot spring is heated by geothermal heat from the Earth's astenosphere. In general, the temperature of rocks increases with depth. The rate of temperature increase is known as the geothermal gradient (it is about 25°C per km). If water percolates deeply enough into the crust, it will be heated as it comes into contact with hot rocks. Warm springs are sometimes the result of hot and cold springs mixing but may also occur outside of volcanic areas. Geysers Geyser are located near active volcanic areas, and the geyser effect is due to the proximity of magma. Surface water works its way down to an average depth of around 2,000 mt where it contacts hot rocks. The resultant boiling of the pressurized water results in the geyser effect of hot water and steam spraying out of the geyser's surface vent (a hydrothermal explosion) Geysers The formation of geysers is due to three particular hydrogeological conditions: 1.A source of water Most of the water in a geyser arrives as rain or snow. It seeps deep into the ground and then makes its way back up. This round trip may take hundreds or thousands of years 2.A source of heat Geysers are located near some sort of volcanic heat source (magmatic chamber). The majority of all geyser fields lie above large bodies of rhyolite (felsic). The water becomes superheated from the molten rocks. 3.A plumbing system The main component of this system is rhyolite, with a high content of silica (SiO2). As the hot water rises, it dissolves the silica and carries it along. SiO2 then precipitates and forms a sinter (a chemical sediment of porous silica) lining the passageways. This makes a constriction which increases the pressure and temperature of the whole system. When the breaking point is reached, the steam and water are forced out from the vent (eruption) Major geyser fields and their distribution Geysers are quite rare, requiring a combination of water, heat, and specific geology. The combination exists in few places on Earth. •Yellowstone National Park, U.S.A.: contains hundreds geysers. It is home to half of the world's total number of geysers in its geyser basins. •Valley of Geysers, Russia: located in the Kamchatka Peninsula is the only geyser field in Eurasia and the second largest concentration of geysers in the world. •El Tatio, Chile: "El Tatio" means "the grandfather" and is located on the Andes surrounded by many active volcanoes in Chile at around 4200 mt a.s.l. •Taupo Volcanic Zone, New Zealand: located on New Zealand's North Island, it lies over a subduction zone in the Earth's crust. •Iceland: due to the high volcanic activity in Iceland, it is home to some famous geysers in the world. Geysers and hot springs are distributed all over the island. “The Great Geysir”, which first erupted in the 14th century, gave rise to the word geyser. Valley of Yellowstone Iceland Geysers El Tatio Taupo Fumaroles A fumarole (Latin fumus, “smoke”) is an opening in a crust, often in the neighborhood of volcanoes, which emits steam and gas such as carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), and hydrogen sulfide (H2S). The steam is created when superheated water turns to steam as its pressure drops when it emerges from the ground. The name solfatara, from the Italian zolfo, is given to fumaroles that emit sulfurous gases. Fumaroles Fumaroles may persist for decades or centuries if they are above a persistent heat source. Hydrogen sulfide (H2S), one of the typical gases issuing from fumaroles, readily oxidizes to sulphuric acid and native sulfur (solid). This accounts for the intense chemical activity and brightly colored rocks in many thermal areas. Fumaroles: Solfatara The most famous fumarole is the Solfatara, a shallow volcanic crater at Pozzuoli, near Naples, part of the Campi Flegrei volcanic complex. It is a dormant volcano (last eruption in 1198), which still emits jets of steam with sulfurous fumes. Fumaroles: Solfatara The name comes from the Latin, Sulpha terra, "land of sulfur". It was formed around 4000 years ago. The crater floor is a popular tourist attraction, as it has many fumaroles and mud pools. The vapours have been used for medical purposes since Roman times. Biology of the hot springs The specific colors of hydrothermal springs derive from the fact that, despite the harsh conditions, life is often found in them in the form of thermophilic bacteria. Some bacteria even prefer temperatures higher than the boiling point of water. Hyperthermophiles grow better at temperatures as high as 80 to 110 °C. As they have heat-stable enzymes that retain their activity even at high temperatures, they have been used in manufacturing antibiotics, plastics, detergents and fermentation. Among these, the first discovered and the most important for biotechnology is Thermus aquaticus..