**6. Applications**

The picture of the Krafla system painted here, if a general case, would imply that magma-related geothermal systems contain far more energy, with higher enthalpy fluids, and are more sustainable than would otherwise be expected. The key may be to penetrate the MHB, by drilling and thermal cracking, so that hydrothermal fluid gains access to the magma itself. Convection within the magma, supplying latent heat of crystallization, enthalpy of magmatic vapor phase from a voluminous source, combined with continued thermal cracking due to energy extraction, could maintain thermal power output without or with lesser need of makeup wells. We need to test this scenario with space-continuous samples and temperature measurements through the MHB at Krafla, and at multiple points in time. We also need to improve geophysical techniques for imaging magma. Such prospecting tools have been tested against reality and improved through much drilling experience in the case of oil and gas reservoirs, but this was never, until now, possible for testing the imaging of magma reservoirs.

There are also large challenges in drilling engineering and technology, because for superhot geothermal power generation, production wells must be sustainable over a long period. This challenge encompasses casing alloys, accommodation of thermally induced stresses in casing, cementing at high pressure and temperature, corrosion and precipitation by and from acid fluids, and extreme sensor technology. The objection that truly high-grade geothermal systems are too far from the customer base to be viable is diminished by recent applications of High Voltage Direct Current (HVDC) technology that enables transmission of electrical power over grea<sup>t</sup> distances, including under the ocean, without losses due to the conductor skin e ffect and external inductive field of AC.

Development of extreme sensor technology, now underway for combustion engine and planetary exploration applications, opens another use for which there is a compelling need: monitoring of restless volcanoes and forecasting of eruptive events [12,53]. All the sensors used to date for volcano monitoring, which measure thermal and gas emission, surface deformation, and seismicity, are in essence remote sensing techniques that are interpreted but not tested against ground truth to reflect processes in the source magma that may or may not lead to eruption. Direct measurement of conditions within or at least proximal to magma bodies would test and improve these interpretations and in the case of very high risk volcanoes might partially supplant labor-intensive surface-based multisensor networks themselves. Monitoring temperature in magma is already within our grasp. Inflation, increased CO2 and thermal emission, and increased seismicity are often interpreted as the rise of new magma into a shallow magma chamber, portending an eruption. This should quickly cause a temperature rise in the convecting magma body being intruded and therefore detected and quantified by in situ sensors. Another, and perhaps simpler question that could be answered, and always arises during periods of volcano unrest, is: are the geophysical and geochemical signals a consequence of underlying magmatic processes or merely reflecting of some structural reconfiguration within the hydrothermal system?

Accidental drilling encounters with magma are beginning to provide new insights into the relationship between magma and hydrothermal systems. Encounters planned for scientific and engineering objectives, as, for example, proposed for the Krafla Magma Testbed (KMT) [12,54], have the potential to lead to a new, much need clean bedload electric energy source and a reliable means to warn populations at risk of impending eruptions The scientific, geothermal energy, and

volcanic hazard needs are compelling. It seems likely therefore that planned explorations of this new frontier are both essential and inevitable.
