Гејзер

Извор Строкир на Исланду, земљи ватре и леда

Гејзер (енгл. Geyser) или гејзир (исл. Geysir) назив је за посебни тип термалних извора који повремено избацује млаз вреле воде у висину. Реч потиче од назива првог континенталним Европљанима познатог исландског гејзера — Гејсира. Тај назив, пак, потиче од глагола гејса (исл. geysa) у значењу куљати, шикљати, брзо истицати. Корен речи је из старонордијског.

Температура воде у гејзерима је око 80°C, а у дубини пукотине из које избијају и до 140°C. Начин избијања воде описује се као водоскок у одређеним временским интервалима. Тај интервал се креће од неколико минута до неколико дана.

Термоминерални водоскок Гејзир у склопу Сијаринске Бање

Гејзери се налазе на местима са вулканском активношћу у прошлости, али и на тренутно вулканско-сеизмички активним локацијама. Највише их има на Исланду, Северној Америци и Новом Зеланду. Најпознатији су новозеландски Вајмангу, активан до 1904, а који је једном приликом избацио стуб вреле воде висок 457m и тежак 800t, као и Стари Верни у америчком националном парку Јелоустоун, у којем се иначе налази око 3.500 оваквих извора вреле воде.

У Србији је одмориште Сијаринска бања (у истоименом градском насељу) познато по гејзеру са минералном и топлом водом. У питању је јединсвена туристичка и геолошка појава, првенствено због свог случајног настанка. Сијарински гејзер није природан, већ је настао приликом истражних бушења новембра 1954. године. Тада је наједном избио термоминерални стуб висок 8m. Тренутна издашност овог извора је 3-5l/s воде температуре 68°C. Постоји и гејзер на обронцима Копаоника висине око 10m.

Etymology

The term 'geyser' in English dates back to the late 18th century and comes from Geysir, which is a geyser in Iceland. Its name means "one who gushes".

Form and function

Steamboat Geyser in Yellowstone National Park

Geysers are nonpermanent geological features. Geysers are generally associated with volcanic areas.Шаблон:Better source needed As the water boils, the resulting pressure forces a superheated column of steam and water to the surface through the geyser's internal plumbing. The formation of geysers specifically requires the combination of three geologic conditions that are usually found in volcanic terrain: intense heat, water, and a plumbing system.Шаблон:Better source needed

The heat needed for geyser formation comes from magma that needs to be close to the surface of the earth. In order for the heated water to form a geyser, a plumbing system (made of fractures, fissures, porous spaces, and sometimes cavities) is required. This includes a reservoir to hold the water while it is being heated. Geysers are generally aligned along faults.Шаблон:Better source needed

Eruptions

Strokkur geyser erupting (clockwise from top left) Steam rises from heated water Pulses of water swell upward Surface is broken Ejected water spouts upward and falls back down into the pipe

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. In non-eruptive hot springs, the geothermally heated water then rises back toward the surface by convection through porous and fractured rocks, while in geysers, the water instead is explosively forced upwards by the high pressure created when water boils below. Geysers also differ from non-eruptive hot springs in their subterranean structure; many consist of a small vent at the surface connected to one or more narrow tubes that lead to underground reservoirs of water and pressure tight rock.

As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, i.e. to remain liquid at temperatures well above the standard-pressure boiling point.

Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins which forces steam bubbles to rise to the top of the column. As they burst through the geyser's vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water below. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser vent.Шаблон:Better source needed

General categorization

Fountain Geyser erupting from the pool (left) and Old Faithful geyser (cone geyser having mound of siliceous sinter) in Yellowstone National Park erupts approximately every 91 minutes (right).

There are two types of geysers: fountain geysers which erupt from pools of water, typically in a series of intense, even violent, bursts; and cone geysers which erupt from cones or mounds of siliceous sinter (including geyserite), usually in steady jets that last anywhere from a few seconds to several minutes. Old Faithful, perhaps the best-known geyser at Yellowstone National Park, is an example of a cone geyser. Grand Geyser, the tallest predictable geyser on earth, (although Geysir in Iceland is taller, it is not predictable), also at Yellowstone National Park, is an example of a fountain geyser.

There are many volcanic areas in the world that have hot springs, mud pots and fumaroles, but very few have erupting geysers. The main reason for their rarity is because multiple intense transient forces must occur simultaneously for a geyser to exist. For example, even when other necessary conditions exist, if the rock structure is loose, eruptions will erode the channels and rapidly destroy any nascent geysers.

Geysers are fragile phenomena and if conditions change, they may go dormant or extinct. Many have been destroyed simply by people throwing debris into them while others have ceased to erupt due to dewatering by geothermal power plants. However, the Geysir in Iceland has had periods of activity and dormancy. During its long dormant periods, eruptions were sometimes artificially induced—often on special occasions—by the addition of surfactant soaps to the water.

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Спољашње везе

• Geysers and How They Work by Yellowstone National Park
• Geyser Observation and Study Association (GOSA)
• GeyserTimes.org
• Geysers of Yellowstone: Online Videos and Descriptions
• About Geysers by Alan Glennon
• Geysers, The UnMuseum
• Johnston's Archive Geyser Resources
• The Geology of the Icelandic geysers by Dr. Helgi Torfason, geologist
• Geysers and the Earth's Plumbing Systems by Meg Streepey
• National Geographic
•  „Geysers”. Encyclopaedia Britannica. 10 (9th изд.). 1879.