The Mývatn area is on the plate boundary of North Iceland. In addition, special stress from below is added by mantle currents. Steam leaks from the groun all around the road leading to the Mývatn Nature Baths.
Exceptional activity as found near Mývatn can be explained, as seen on the map below.
North-east of Mývatn is a geothermal wonderland, that can only be explained with this line of mantle convection underneath. The line is of double nature, because it both stands for division between small rolls of upper mantle, and also that of the large scale rolls of lower mantle. Mývatn is located directly over the big convection rolls responsible for creating the Atlantic Ocean.