**7. Conclusions**

Existing in situ data from magma bodies are few and without precedent. Data from Krafla confirm the existence of an MHB such as found in lava lake drilling and predicted from theoretical considerations. The MHB at Krafla is remarkably thin. However, with such sparse data, it is not possible to say how representative Krafla is of magma–hydrothermal systems in general. Combining Krafla results with insights from the two other sites of magma encounters and results from lava lake drilling, it is suggested that:


**Funding:** I benefited from workshops on the Krafla Magma Testbed supported by Landsvirkjun National Power Company, International Continental Scientific Drilling Program (ICDP), and the US National Science Foundation (NSF). In addition, I received travel support from Landsvirkjun, Iceland; the Geothermal Research Group (GEORG), Iceland; and the British Geological Survey.

**Acknowledgments:** Thanks are due for discussions with many colleagues involved in the Krafla Magma Testbed Project and for the pioneering work of IDDP. I am especially grateful to Charles Carrigan, Yan Lavallee, Allen Glazner, and Pavel Izbekov for stimulating insights, many of which are cited here, but that is not to say that they agree with everything herein. Charles Carrigan and Pavel Izbekov contributed to magma viscosity calculations.

**Conflicts of Interest:** I declare that I have no competing financial interests or personal relationships that could have influenced the work reported in this paper.
