| Abstract |
Since the settlement of Iceland in the ninth century AD, people have used geothermal water for bathing, washing, cooking and even house heating. In spite of this utilization, only few speculative thoughts appear in the Sagas and contemporary records on the origin and nature of the hot water. In the 18th century, the first visitors with some scientific training came to Iceland and research on geothermal activity began. One of the first ideas was that the heat and fumarolic activity was caused by fermentation in surface layers. It was a breakthrough when the German scientist and father of modern chemistry, Robert Bunsen, came to Iceland in 1846. He investigated several geothermal fields in Iceland and took samples for later analysis. He came to the conclusion that the geothermal water was originally rainwater which had precipitated deep into the earth and been heated by the surrounding rocks. He and his colleagues explained the chemical composition of the geothermal water solely as water-rock interactions. Very soon, these findings of Bunsen were forgotten or were never absorbed by the geological scientific community. In the late 19th and early 20th centuries, most geologists thought that geothermal water was mostly juvenile water originating in magma. However, in the first decades of the 20th century, most researchers returned to the conclusion that it was originally rainwater but was heated either by magma or by cooling intrusions at depth, as Bunsen had proposed. Around 1940, Icelandic geophysicist Trausti Einarsson criticized this heating-mechanism. He argued that the convecting water was heated by the surrounding rock. Einarsson thought that the geothermal water and the crust were in steady-state equilibrium with the flow of heat from the mantle up through the crust. This model of a geothermal system is called the "steady-state model". Another Icelandic geophysicist, Gunnar Bˆdvarsson, demonstrated around 1950 that the steady-state heat flow is not sufficient to maintain the power of all the geothermal systems in Iceland; and he proposed that the geothermal systems are a transient phenomena created by local circulation of groundwater in faults and fissures. Thus, the circulating water was mining heat from the lower part of the crust and transferring it to the upper part, creating the hot spring areas. This model is called the "heat mining model". Strangely enough, the steady-state model was generally accepted in the geothermal community in Iceland but the heat-mining model was forgotten for 30-40 years until Bˆdvarsson republished his work in an international journal in 1984. Now the "heat mining model" is generally accepted and explains all the major features of low-temperature geothermal systems in Iceland. It is interesting to compare this erratic development of thought on the nature of geothermal systems with the discovery, rejection and re-discovery of other ideas in geology such as Wegener's continental drift theory. |