Heat Sources in Low-Temperature Geothermal Systems, New Zealand

Abstract

Low-temperature geothermal resources are ubiquitous in onshore New Zealand, where heat can be harnessed directly from the rock, e.g., using ground source heat pumps (GSHP), or transported by fluids in thermal spring systems, abandoned underground mines and wells. Radioactivity is the pervasive source of crustal heat but geological and hydrological regimes generate additional heat and enhance heat and mass transfer to depths where heat extraction is economical. These include volcanism, mantle diapirism, crustal heat from rapid uplift and advection of hot fluids from depth through favorable channels. Exothermic chemical reactions and sustained shear heating at fault planes may be localized and possibly, short-lived heat sources. Heat harnessed from the ground by GSHP may be augmented in cities by urban heat islands.