Geothermal energy

The geothermal area in Brennisteinsfjöll

The geothermal area in Brennisteinsfjöll lies at 400-500 m above sea level. Active geothermal heat appears as steam at about 450 m height, but cold alteration is in four places and bears witness to greater activity in earlier times. Geothermal heat at the surface is insignificant, and based on the extent of geothermal heat and alteration the area is about 3 km2. Resistivity measurements indicate that the area is about 18 km2 at 700 m depth below sea level, about 1200 m below the surface where geothermal heat is detected. The high-temperature area in Brennisteinsfjöll lies in the eponymous fracture swarm, and there have erupted there at least 30-40 times since the Ice Age ended. Fault lines are young in the area from the sea north to Mosfellsheiði, and earthquakes often occur in a belt about 5 km wide and about 40 km long. Earthquakes in Brennisteinsfjöll can become fairly large. The main type of strata is tuff, and where eruption sites have reached up out of the glacier, lavas have flowed and table mountains or lava ridges have formed. All rock formations are basalt, and no acidic or intermediate rock has been found at the surface.