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The Okataina groundwater catchment (OGC), with the Okataina caldera complex and its large caldera structures and rhyolite domes, 11 lakes, numerous shallow, cold, groundwater systems and 15 geothermal fields, is a spectacular part of the Taupō Volcanic Zone (TVZ) and an example of the many meteoric-dominated hydrothermal systems, ancient and modern, that bound the Pacific Ocean. This paper describes Quaternary OGC evolution in four phases with 4D models of geology and groundwater-geothermal systems. The early-TVZ Proto-KWG phase had development of the KWG graben, the Proto-Tarawera River and catchment, and ended with deposition of Whakamaru Group ignimbrites, sourced south of the OGC. Then, Matahina phase volcanism resulted in the Matahina caldera with Matahina Formation ignimbrite deposited over a wide area within, and beyond, the OGC. Groundwater flowed into Lake Matahina which was the location of multiple geothermal fields. Thirdly, the Penultimate phase produced the Rotoiti caldera, Lake Haroharo, and two OGC ignimbrites, i.e., Rotoiti Formation and Earthquake Flat Formation. Lake Haroharo recieved inflow from groundwater-geothermal systems. Lastly, the Infill phase resulted in today's major OGC landforms, e.g., the Mt. Tarawera and Haroharo domes, multiple lakes, their catchments, groundwater systems and geothermal fields. Deep drilling is recommended to address key science gaps, i.e., the locations and properties of subsurface caldera-lake sediments and the processes (chemical and physical) of fluid flow from deep geothermal reservoirs to surface hydrothermal areas. • Pleistocene Okataina groundwater catchment (OGC) geology and groundwater-geothermal systems evolved in four phases • The 'proto-Kapenga–Whakatane Graben phase' preceded 'Matahina phase' Matahina caldera, ignimbrites and Lake Matahina. • 'Penultimate phase' Rotoiti caldera, ignimbrites and lakes were followed by 'Infill phase' volcanism, e.g., Mt Tarawera. • Hydrothermal systems are meteoric-dominated as rainfall recharge typically provides more than 79% of system spring flow. • Most current–day hydrothermal systems were formed in the two OGC caldera-forming phases and associated with caldera lakes. [ABSTRACT FROM AUTHOR]

Volcanism has affected the environment of our planet over a broad range of spatial (local to global) and temporal (< 1 yr to 100s Myr) scales and will continue to do so. As well as examining the Earth's geological record and using computer modelling to understand these effects, much of our knowledge of these processes comes from studying volcanism on the present-day planet. Understanding the full spectrum of possible routes and mechanisms by which volcanism can affect the environment is key to developing a realistic appreciation of possible past and potential future volcanic impact scenarios. This review paper seeks to give a synoptic overview of these potential mechanisms, focussing on those that we can seek to understand over human timescales by studying current volcanic activity. These effects are wide ranging from well-documented planetary-scale impacts (e.g., cooling by stratospheric aerosol veils) to more subtle or localised processes like ash fertilisation of ocean biota and impacts on cloud properties, atmospheric oxidant levels and terrestrial ecosystems. There is still much to be gained by studying present-day volcanic emissions. This review highlights the need for further work in three example areas. Firstly, to understand regional and arc-scale volcanic emissions, especially cycling of elements through subduction zones, more volatile measurements are needed to contribute to a fundamental and systematic understanding of these processes throughout geological time. Secondly, there is still uncertainty surrounding whether stratospheric ozone depletion following volcanic eruptions results solely from activation of anthropogenic halogen species. We should be poised to study future eruptions into the stratosphere with regard to their impacts and halogen load and work to improve our models and understanding of the relevant underlying processes within the Earth and the atmosphere. Thirdly, we lack a systematic understanding of trace metal volatility from magmas, which is of importance in terms of understanding their geochemical cycling and use as tracers in environmental archives and of igneous processes on Earth and more broadly on silicate planetary bodies. Measurements of volcanic rock suites and metals in volcanic plumes have an important part to play in moving towards this goal. [ABSTRACT FROM AUTHOR]

The western slope of Cerro Domuyo in northern Patagonia is characterized by thermal springs with boiling waters, Quaternary silicic domes, and pyroclastic deposits that suggest the existence of a geothermal reservoir. According to geochemical studies, the reservoir may have a temperature of 220 °C and one of the largest advective heat fluxes reported for a continental volcanic center. In this paper, we propose a more refined conceptual model for the Domuyo geothermal area, based on a geological survey supported by U Pb, U Th, and Ar Ar geochronology and by magnetotelluric and gravity surveys. Our study indicates that the Domuyo Volcanic Complex (DVC) is a Middle Pleistocene dome complex overlying middle Miocene to Pliocene volcanic sequences, which in turn cover: 1) the Jurassic-Early Cretaceous Neuquén marine sedimentary succession, 2) silicic ignimbrites dated at ~186.7 Ma, and 3) the Paleozoic metamorphic basement intruded by ~288 Ma granite bodies. The volcanic cycle in the DVC is distinctly bimodal, characterized by the emplacement of massive silicic domes and less voluminous olivine basalts on its southern slope. A major collapse of the central dome at ~600 ka produced a voluminous (19.4 km3 and 133 km2) block-and-ash flow, and associated pyroclastic flows, that filled a valley to the southwest at distances up to ~30 km from Cerro Domuyo summit. This was followed by a period of intense effusive activity that formed the Cerro Guitarra, Cerro Las Pampas, Cerro Domo, and Cerro Covunco silicic domes. The last two domes are the youngest and largest edifices, dated at 0.50 Ma (Ar Ar age) and 0.25 Ma (U Th age). Pre-Cenozoic successions were affected by N-S reverse and thrust faults that were later displaced by an ENE-WSW-trending transtensional belt. The basement rocks at the northern termination of the Cordillera del Viento anticlinorium were also displaced towards the east-northeast by this belt, which is observed NNW of Cerro Domuyo. The DVC was emplaced within this zone of crustal weakness. The integration of geologic observations with magnetotelluric and gravity data, allowed us to develop an updated conceptual model of the geothermal system. The geothermal reservoir is inferred at a depth of less than 2 km within pre-Pliocene fractured rocks, bounded by ~WSW-ENE trending faults and sealed by the pyroclastic deposits and rhyolitic lavas of the DVC. The location of most thermal springs is not directly controlled by faults. Instead, flows emerge at the contact between the fractured and faulted basement and the caprock. • The Domuyo Volcanic Complex (DVC) is a silicic dome complex formed in the Pleistocene. • The central dome collapsed at ~600 ka producing a voluminous (19.4 km3) pyroclastic deposit. • The youngest domes were emplaced at ~500 ka and 250 ka. • The DVC was emplaced within a ENE-WSW trending transtensional zone of crustal weakness. • The geothermal reservoir is hosted in pre-Pliocene rocks sealed by the DVC pyroclastics and lavas. [ABSTRACT FROM AUTHOR]