Natural processes leading to large, pre-historic hydrothermal eruptions in geothermal areas: Rotokawa geothermal field, New Zealand
Por:
Montanaro C., Cronin S.J., Lerner G.A., Simpson M.P., Brooks-Clarke I., Swanney G., Milicich S.D., Calibugan A., Bardsley C., Scheu B.
Publicada:
1 ene 2024
Ahead of Print:
1 abr 2023
Categoría:
Geology
Resumen:
Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The largest of these may produce kilometer-sized craters and breccia deposits that are tens of meters thick. The geological and hydrothermal priming that leads to these types of eruptions is poorly understood. To understand large hydrothermal eruptions, we investigated a series of prehistoric events at the Rotokawa geothermal field in New Zealand. By revising the stratigraphy and distribution of hydrothermal breccia deposits and correlating these with componentry, crater morphology, and subsurface geological structure, we estimated the frequency, priming processes, triggers, and dynamics of multiple eruptions. Seventeen large hydrothermal eruptions occurred centuries to millennia apart in the period from ca. 22 cal ka B.P. to ca. 3.4 cal ka B.P. Of six hydrothermal eruptions since ca. 7 ka, four produced oval-shaped craters up to 2 km in diameter, creating a broad, shallow depression within the geothermal field. The two youngest eruptions occurred northeast of earlier eruption centers and have narrower and elongated vents. We infer that in the central depression, newly formed craters rimmed by breccia deposits and high-relief country rock hosted temporary lakes tens of meters deep. Crater-lake breakout(s) and/or seismic events caused sudden pressure reduction above the hydrothermal aquifer, trigger ing hydrothermal eruptions. Northeast of the basin, hydrothermal alteration produced caprocks above intensively fractured areas. In this case, earthquakes are the most likely trigger for cap-rupture and eruption. All eruptions excavated shallow and large craters mostly within partially altered Oruanui Formation and pre-fragmented breccias. The size and localization of the eruptions was likely due to a combination of (1) availability of undisturbed porous ignimbrite hosting large thermal aquifers, (2) efficient crater excavation within or alongside pre-fragmented breccia, and (3) the location of fracture and fault zones that channeled deep fluid upflow, favoring priming processes. This study highlights how an interplay of tectonic, magmatic, and hydrologic processes is responsible for the timing, dynamics, and ultimate size of hydrothermal eruptions in geothermal fields. Some events may be very large and destructive depending on the right priming and geological conditions. © 2024 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. All Rights Reserved.
Filiaciones:
Ludwig-Maximilians-Universität München, Theresienstrasse 41, Munich, 80333, Germany
School of Environment, University of Auckland, Science Centre, Building 302 23 Symonds Street, Auckland Central, New Zealand
Instituto de Geofísica, Universidad Nacional Autónoma de México, CDMX, Coyoacán, 04150, Mexico
GNS Science, Wairakei Research Centre, Taupo, 3352, New Zealand
GNS Science, Avalon Research Centre, Lower Hutt, 5010, New Zealand
Mercury NZ Ltd., PO Box 245, Rotorua, 3040, New Zealand
Bronze, Green Submitted, All Open Access; Bronze Open Access; Green Open Access
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