Topography as a Major Influence on Geothermal Circulation in the Taupo Volcanic Zone, New Zealand

• Published in: Geophysical research letters 2021-04, Vol.48 (8), p.n/a
• Main Authors: Pearson‐Grant, S. C., Bertrand, E. A.
• Format: Article
• Language: English
• Subjects: electrical resistivity; geothermal; numerical modeling; Taupo Volcanic Zone; topography
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL092248

Geothermal systems are an important resource in the global effort to reduce fossil fuel use. They are formed by convection of water heated at depth, but without external controls convection is unstable and upflows move or dissipate. In the central Taupo Volcanic Zone in New Zealand, the geothermal systems have been in the same locations for more than 50 kyr. We created heat and fluid flow models with uniform geology and basal heat which showed that the known topography localizes convective upflows. Fourteen out of 19 known geothermal systems in the model area were correctly located beneath topographic lows. Even at 3 km depth, inclusion of topography in our models improved agreement between the locations of upflows and low‐resistivity zones derived from 3‐D inversion of magnetotelluric data. Therefore, while topography is not the only factor that influences geothermal convection, its contribution is on a larger scale than is generally assumed. Plain Language Summary Geothermal systems are a clean, renewable energy source. They are created by water that is heated at several kilometers depth and rises to the surface in distinct “plumes.” We don't know why the plumes rise where they do or why they seem to stay in the same place for hundreds of thousands of years. We used specialized computer code to look at whether topography can keep these plumes in place. With uniform geology and heat flow at depth, our simplified models show that high topography can drive water downwards even at 3 km depth. The geothermal systems form between these highs, in valleys and topographical lows. Faults and localized heat sources will also be playing a part, but topography is known accurately and can explain the locations of 14 of the 19 geothermal systems in the Taupo Volcanic Zone, New Zealand. Before, it was thought that topography mainly affected nearby shallow fluid flow. Future geothermal exploration and modeling of warm water extraction should take these results into account. Key Points Geothermal systems in the Taupo Volcanic Zone are long‐lived and stable, which requires non‐uniformity Topography can provide this non‐uniformity and explain the locations of 14 of 19 geothermal systems in our fluid and heat flow model area Topographically driven convection can extend to several kilometers depth, even with moderate surface relief