Bitra

The Hengill Area is one of Iceland‘s largest geothermal areas, approximately 100 km² in size. That is not to say it is all one and the same cauldron, but rather a composite of the Hveragerði volcano (Grændalur), Ölkelduháls and the geothermal area of the Henglafjöll mountains

Considerable power plant construction has already taken place in the area, including power plants at Hengill and Nesjavellir. In the 2nd phase of the Master Plan for Hydro and Geothermal Energy Resources, further proposals for power plants at Grændalur and Bitra are classified as protected, proposals at Gráuhnúkar, Hellisheiði, Hverahlíð and Meitillinn are classified as exploitable, while projects at Innstidalur, Ölfusdalur and Þverárdalur await further assessment.

The hot springs and geysers with siliceous sinter deposits at Hveragerði and Reykjar are characteristic of the Grændalur area, along with the numerous natural springs that are formed during rockslides. Steam fumaroles are common in the area and often coincide with cracks formed in the large earthquakes that periodically hit South Iceland.

At Ölkelduháls, there is a lot of geothermal activity of various kinds. Numerous large mudpots, muddy hot springs and fumaroles are dotted around the area. In several places, vestiges of powerful steam explosions can be found. Mineral salt and sulphuric deposits predominate. At Klambragil canyon at the bottom of Reykjadalur valley, great bubbling hot springs can be found, from which a hot stream runs before joining a colder current and creating an optimal bathing spot in the river Reykjadalsá.

A large portion of the area is on the Nature Conservation Register, i.e. the drainage basin of Grændalur valley, Reykjadalur valley and Hengladalir valleys. There are several popular hiking routes in the area.

Photo © Mats Wibe Lund

Bitra is a wide dolerite ridge that gently rises as it stretches northwards from Hellisheiði. To the west lie the Henglafjöll mountains, and to the east a series of tuff and pillow lava ridges formed in volcanic eruptions reaching from Hrómundartindur mountain in the north to the Molddalahnúkar mountains in the south.

The Ölkelduháls ridge lies between Tjarnarhnúkur and Ölkelduhnúkur. An unusual phenomenon in the area is a group of carbonated pools stretching from Ölkelduháls south to Reykjadalur valley and Hverakjálki.

The area is considered important for outdoor recreation for residents of nearby urban areas. The Hengill area is a natural treasure and Þorlákshafnarsel, Hellurnar and Hellukofinn enjoy protected status.

The series of valleys comprised of Reykjadalur, Grændalur, Fremstidalur and Miðdalur, along with the Ölkelduháls ridge, will most likely form a contiguous conservation area in the future.

Photo © Hlynur Stefánsson

Orkuveita Reykjavíkur plans to build the proposed 90 MW Bitra Power Plant in the Hengill area, primarily harnessing energy from the Ölkelduháls geothermal area.

The geothermal area is believed to be connected to the magma chamber of a moribund volcanic system, and eruptions at Bitra and Tjarnarhnúkur towards the end of the Ice Age caused lava flows in the area. The stratum is however largely made up of tuff. Geothermal activity is spread over a fairly large area. To the west it reaches from Kýrgil canyon south to Hverakjálki, while further east it stretches from Lakaskörð south to Grændalur valley. The Bitra Power Plant would also affect the geothermal areas in the valleys of Fremstidalur and Miðdalur at Hengill.

In an assessment carried out by Orkustofnun, the Hengill area is included as part of one big area covering 100 km². Production capacity is estimated at 710 MW for a period of 50 years, or 385 MW for 100 years, and as such is the second most powerful geothermal area in Iceland after the Torfajökull area. Power production in the area is already at 420 MW.

The Hengill area is defined as covering 112 km² and includes the Hveragerði geothermal area in an assessment carried out for the Bitra Power Plant. Based on Orkustofnun‘s assessment, the Hengill area must be considered fully exploited already. Orkuveita Reykjavíkur‘s plans for a hydroelectric power plant at Ölkelduháls are currently awaiting further assessment.

Photo © Hlynur Stefánsson