|Lava flowing from Krafla, U.S.G.S. photo|
Expecting to find deep magma, at 4.5 kilometers, the scientists instead found magma flowing into their drilled well at 2.1 kilometers! Even more unexpectedly, although the dominant rock at Krafla is basalt (containing 45-50%) silica, the magma that they encountered was rhyolite (containing 65-70% silica). This confirmed the hypothesis that rhyolites can form by partial melting of basalts.
Drilling into hot environments, and extracting hot water from them, is extremely difficult for several reasons: any hot water encountered is likely to be laden with minerals that can precipitate out in pipes, and the rocks become very soft. When they reached 2 km depth, the drill bit froze up (would not rotate). When they tried to extract the bit, it became stuck. They found that an intrusion of magma had filled the bottom 9 meters of the well, so they stopped exploratory drilling and converted the well to a production well. The well produced dry steam at a temperature of 400 C (dry steam is water vapor that is heated to temperatures much higher than the boiling temperature at the pressure of the source; wet steam is steam that is in equilibrium with liquid water at the same pressure.) To give you a feel for the potential magnitude of this resource, this steam is hot enough to potentially power 25,000-30,000 homes. 95% of the homes in Iceland are heated with geothermal resources.