The most audacious vision for geothermal is to drill six miles or more underground where temperatures exceed 750 degrees Fahrenheit. At that point, water goes supercritical and can hold five to 10 times as much energy as normal steam. If it works, experts say, “superhot” geothermal could provide cheap, abundant clean energy anywhere.
Folks in Finland recently tried exactly that, drilling 2 holes 6.4 km deep in Otaniemi, Vantaa. Unfortunately their fracking attempts failed and sufficient flow could not be established between the two wells. Also, temperature at the bottom was 120 C, not enough to get supercritical water (374 C is required). They donated the boreholes to scientific use, someone will try again and try better…
Once the “how” can be sorted out, it should be usable anywhere on Earth, not just volcanic regions. :) But it’s not easy.