The volcano is an important source of energy for the south of the country, which is captured at the Nesjavellir power station (near the western shore of the lake Þingvallavatn) and the Hellisheiði power station (approximately 11 km south and west of Nesjavellir).
However research has shown that large quantities of water flow in sub-surface streams to lake Þingvallavatn (some 50 km to the south and easily accessible to tourists) and reappear in springs in and around the lake, while the same happens on the west side, giving rise to various tributaries of the Hvítá River as well as some rivers flowing north towards Húnaflói.
The name is a tautology, consisting of the word "loch" (of Gaelic origin) and vatn, a Norse word meaning the very same, found in such names as "Þingvallavatn" and Myvatn in Iceland, and "Røssvatnet" and "Møsvatn" in Norway.
In the past, melting ice from the glacier would run through a river directly into the Þingvallavatn Lake.
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About 50 kilometers north of the Þingvallavatn Lake lies the home of Iceland's second largest glacier Lángjökull.
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From this point, it takes a drop of water between 30 and 100 years to travel 50 kilometers to the Þingvallavatn Lake in the Þingvellir National Park.
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Silfra, by virtue of its location in the Þingvallavatn Lake, contains clear, cold water that attracts scuba divers drawn to its high visibility and geological importance; divers are literally swimming between continents.
The extensive lava fields which were produced by this eruption, flowed southwards, and formed the basin of Þingvallavatn, Iceland's largest lake, and Þingvellir, the "Parliament Plains" where the Icelandic national assembly, the Alþing was founded in 930.