Final answer:
Geothermal energy can be reused sustainably if managed properly, and while it's abundant in regions with geological hotspots, the overall sustainability and scale-ability for global energy needs are challenging due to variations in geothermal activity and potential depletion near extraction sites.
Step-by-step explanation:
Geothermal energy can indeed be reused, but only to a certain extent and under specific conditions. The sustainability of geothermal energy depends on the balance between the rate of energy extraction and the natural replenishment rate of geothermal heat, which is mainly from radioactive decay within the Earth. In regions with geological hotspots, such as near tectonic plate boundaries, geothermal energy can be constantly produced because of the high temperatures resulting from magma. However, this is not the case everywhere.
Geothermal heat can be considered a kind of 'mining' if we extract it faster than the geophysical replacement rate, effectively depleting it. This method leads to incremental drilling to maintain energy production, which may not be sustainable in the long term. Yet, for geothermal systems with heat-exchange that operate just below the surface, these are typically sustainable as they leverage the stable ground temperature for heating in winter or cooling in summer, significantly reducing demands on traditional energy systems.