Iceland is a land of geysers and the greatest of all is situated in the south-west of the island. From a quiet stream-covered pool, Strokkur becomes a seething cauldron that suddenly shoots a column of boiling water high into the air, approximately every four to ten minutes. Strokkur is situated in the geothermal region beside the Hvita River in Iceland, 50 miles (80km) east of Reykjavik. A group of steaming pools of scalding water and bubbling mud is located in this area and it is the site of the Stori Geysir, or Great Gusher, once the most powerful geyser of the group. All other geysers were named after it – the Icelandic word geyser means to gush.
Geysers occur where magma, or molten rock, lies near the Earth’s surface. Water seeps through crevices in the rock to form underground reservoirs. The water is heated by the hot rocks and some eventually turns to steam. A head of steam builds up until it escapes in a huge jet of water and steam, which is known as a geyser.
At regular intervals throughout the day, as if it were triggered by some underworld master of ceremonies, Strokkur hurls its columns of boiling water 70ft (22m) towards the sky. After a few seconds, with a hiss of steam, the fountain subsides and the waters of the surrounding pool calm down. At these times Strokkur becomes a sheet of clear water overhung with steam. The first sign of approaching activity is a fluctuation in the level of the water. As the waters heave with ever-increasing speed, a dome of clear, scalding water wells up for a moment. Then, with a roar, the dome suddenly bursts, and Strokkur repeats its display. No wonder its name means ‘The Churn’ in Icelandic.
At one time the waters of this world-famous hot spring reached the incredible height of 230ft (70m). In 1810 it was active every 30 minutes, yet just five years later the time between eruptions was a much as six hours, and in 1916, all activity ceased. In 1935, after some water had been drained off, for a short time the geyser began to erupt again on its old schedule of every 30 minutes. Then in 2000, after years of inactivity, an earthquake re-voke Stori Geysir, but the frequency of its eruptions is no longer regular. Occasionally technicians prompt it to put on a display by pouring large amount of liquid soap into the pool. This increases the density of the water, which acts like a lid on the geyser, preventing steam from escaping. When some of the soap solution is removed from the vent, the pressure is relieved and the geyser erupts.
Iceland owes its geysers to the fact that it is situated on the Mid-Atlantic Ridge, where two great segments of the Earth’s crust, known as tectonic plates, are moving away from each other. This causes a line of weakness through which molten magma wells up from deep within the Earth. The magma heats underground water which can escape through geysers.
Hot springs and lakes of bubbling mud occur in areas where pockets of molten magma lie close to the surface near underground water, as in the Hvita Valley. The magma heats both the porous rocks and the water which has soaked down through them. When the water can escape freely, it will rise to the surface as a bubbling hot spring or mud pool. If, however, water is partially enclosed in a hollow column in these rocks. It will heat up to a high temperature and create a geyser. The pressure of the water column itself initially prevents the water from boiling.
Heat builds up and eventually the water starts to boil at as much as 11°F (6°C) above normal boiling temperature at the surface – this is known as superheating. Steam pressure builds up and forces the water above the top of the column into a dome in the pool. This, in turn, lowers the pressure allowing more water to boil until, finally, the superheated stream blasts a column of hot water out of the ground as though it were being shot from a giant cannon. When water begins to accumulate in the hollow in the heated rock, the whole cycle starts again.
Since the early 1900s, the Icelandic people have made efficient use of the heat stored below ground. They employ this energy for heating in industry, agriculture and in the home. By 1942, an extensive system of pipes and pumping stations was bringing natural hot water to large storage tanks in the hills overlooking the capital, Reykjavik. The water sources were carefully chosen to avoid disrupting the playing of Strokkur and other geysers. Today. Most homes in the city are plumbed into the natural hot-water system. In other areas, engineers use the volcano rocks to heat cold water pumped down to them.
The power station sited at Svartsengi, on the south-western Reykjanes peninsula, uses geothermal energy. Run-off water from the plant collects in the ‘Blue Lagoon’, a pool which has become well known for curing skin complaints, such as eczema.
The town of Hveragerddhi, south-east of the capital, bears witness to the success of using natural energy. In the town, lying only 155 miles (250km) from the Arctic Circle, tropical house plants and fruits and vegetables, such as bananas and cucumbers, flourish in glasshouses heated by geothermal waters, giving the town its reputation as ‘the garden of hot springs’.