Geothermal activity
Geothermal area
is an area where warm water ascends through fissures, crevices and volcanic crust. Cold rainwater pours down into the porous bedrock, is heated from the old magma chamber and fissures and ascends to the surface as it gets hotter.
Geothermal areas in Iceland are divided into high temperature fields and low temperature fields.
High temperature fields have temperatures of at least 150 degrees Celsius at a depth of 1 km and more are only found in the active volcanic zone along the tectonic plate boundary. Yield water is so rich in gases and minerals that it can not be used in the distribution system. Iths high pressure and high thermal energy make it well suited to heating fresh cold water which then can be used for space heating, and also for generation of electricity. Magma chambers provide the main heat source for these areas' common fumaroles, mudpots and hot springs.
The main high-temperature areas are Torfajökull east of Hekla, Grímsvötn in the Vatnajökull glacier, Hengill near Reykjavík, Kerlingarfjöll, Námafjall near Mývatn, Kverkfjöll on the north side of Vatnajökull and Krísuvík south of Reykjavík.
Low temperature fields have temperatures less than 150 degrees Celsius at a depth of one kilometer and yielding water can be used directly for space heating adn washing. Dead magma chambers or lava flows provide the heat source for these areas' hot springs and geysers.
Low-temperature areas with hot springs are foundable all over Iceland.
Methamorphosis in high temperature area
Yellow colours: Often pure sulphur (The Krysuvik Area).
Red and brown colours: Iron and sulphur (Fe, S), which assimilates with the oxygen of the atmosphere. The sulphur creates yellow colours and the iron red and brown hematite.
Grey colours: are created when sulphuric acids dissolve the basaltic rock. H2S assimilates the oxygen of the ground water and creates H2SO4 and clay minerals are created.
Light colours: are mainly created by Silica (SiO2), Calcium (CaCO3), and sometimes also Gypsum (CaSO4, H2O).
Geothermal features
Iceland's geothermal features (hot springs, mudpots, geysers, and fumaroles) are common in the volcanic zone along the tectonic plate boundary. Here, groundwater and sometimes seawater seep into the ground and travel through highly fractured bedrock. The water reaches varying depths where it comes in contact with heat from volcanic sources. As the water is heated, it ascends through fissures, crevices, and volcanic crust to emerge in hot springs and other geothermal features.
Hot springs
is a spring spring that issues water at temperatures substantially higher than the air temperature of the surrounding region. Most hot springs result from the interaction of groundwater with magma or with solid but still-hot igneous rocks.
The most powerful hot spring in Iceland, Deildartunguhver in Borgarfjörđur, has a flow of about 250 litres of boiling water per second.
More photos of Hot springs
Fumarole
is volcanic vent from which steam and volcanic gases issue. The major source of the steam emitted by fumaroles is groundwater heated by magma. Carbon dioxide, sulfur dioxide, and hydrogen sulfide are usually emitted directly from the magma. A fumarole rich in sulfur gases is called a solfatara; a fumarole rich in carbon dioxide is called a mofette.
More photos of Fumaroles
Mudpot
is a sort of hot spring or fumarole consisting of a pool of usually bubbling mud when hot water rises to the surface at a spot where the soil is rich in volcanic ash, clay and other fine particulates. Mudpots form in high-temperature geothermal areas where water is in short supply.
Mud pots are sometimes called paint pots, when the slurry is particularly colorful.
More photos of Mudpots
Geyser
Geyser is a spouting hot spring derived from Geysir, which itself is derived from the Icelandic verb gjósa meaning to erupt.
The Great Geysir in the Haukadalur valley is the oldest known geyser and one of the world's most impressive examples of the phenomenon.
It is hurl boiling water up to 60 metres in the air and the eruptions are infrequent in the present.
The nerby geyser Strokkur erupts to heights of up to 20 - 30 metres every few minutes.
In Haukadalur valley there are thirty smaller geysers and hot pools, including one called Litli Geysir (Little Geysir).
More photos of Geysers
References:
http://notendur.centrum.is/~nedrias/hga.htm