Obviously geothermal is possible. Equally obvious: it is not economically viable as a global replacement for fossil fuels or it would have supplanted them already, especially in Iceland.
I wonder how the flying in and out is accounted for in these sorts of figures, if hydrocarbons are ever replaced in aviation it will be dead last after everything else.
I found Iceland's "Fuel Use Forecast" at https://nea.is/fuel/forecast/nr/132 , which appear to be from 2007. It shows aviation as the biggest - and growing - consumer of fuel.
This won't involve burning less jet fuel and resembles a Papal indulgence, but maintaining an industrial civilization while decarbonizing industry is impossible without this kind of accounting.