Hydrothermal eruptions are characterised by violent explosions ejecting steam, water, mud, and rock. They pose a risk to tourism and the operation of power plants in geothermal areas around the world. Large events with a severe destructive threat are often intensified by the injection of magmatic fluids along faults and fractures within volcano-tectonic rifting environments, such as the Taupo Volcanic Zone. How these hydrothermal eruptions progress, how craters form and the scale of ejecta impacts, are all influenced by the local geology and reservoir hydrology. By analysing breccia lithology, undisturbed strata proximal to the explosion sites, and conducting tailored decompression experiments, we elucidate the eruption sequence that formed Champagne Pool, Wai-o-tapu, New Zealand. This iconic touristic site was formed by a violent hydrothermal eruption at ~ 700 years B.P. Samples from undisturbed drill cores and blocks ejected in the eruption were fragmented in shock-tube experiments under the moderate pressure/temperature conditions estimated for this system (3–4 MPa, 210–220 °C). Our results show that this was a two-phase eruption. It started with an initial narrow jetting of deep-sourced lithologies, ejecting fragments from at least a 110-m depth. This event was overtaken by a larger, broader, and dominantly shallower eruption driven by decompression of much more geothermal fluid within a soft and porous ignimbrite horizon. The second phase was triggered once the initial, deeper-sourced eruption broke through a strong silicified aquitard cap. The soft ignimbrite collapsed during the second-phase eruption into the crater, to repeatedly choke the explosions causing short-term pressure rises that triggered ongoing deeper-sourced eruptions. The eruption spread laterally also by exploiting a local fault. These results are relevant for hydrothermal eruption hazard scenarios in environments where strong vertical variations in rock strength and porosity occur.

中文翻译：

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反映主岩地质和地热蚀变垂直变化的热液喷发动力学，香槟池，Wai-o-tapu，新西兰

热液喷发的特点是剧烈的爆炸喷出蒸汽、水、泥浆和岩石。它们对世界各地地热区的旅游业和发电厂的运营构成风险。具有严重破坏性威胁的大型事件通常会因岩浆流体沿火山构造裂谷环境（例如陶波火山带）内的断层和裂缝注入而加剧。这些热液喷发的进展方式、陨石坑的形成方式以及喷射物影响的规模，都受到当地地质和水库水文的影响。通过分析角砾岩岩性、爆炸地点附近未受干扰的地层，并进行量身定制的减压实验，我们阐明了形成新西兰 Wai-o-tapu 香槟池的喷发序列。这个标志性的旅游景点是由大约 700 年 BP 的猛烈热液喷发形成的 在该系统估计的中等压力/温度条件下（3-4 兆帕, 210–220 °C)。我们的结果表明，这是一个两阶段的喷发。它从最初的深源岩性狭窄喷射开始，从至少 110 米的深度喷射碎片。这一事件被一个更大、更广、更浅的喷发所取代，该喷发是由更多地热流体在柔软多孔的熔凝岩层内减压驱动的。一旦最初的、来源更深的喷发突破了强大的硅化透水层盖，第二阶段就被触发了。在第二阶段喷发到陨石坑中时，软熔岩坍塌，反复扼杀导致短期压力上升的爆炸，从而引发持续的更深层次的喷发。火山喷发也通过利用局部断层横向扩展。这些结果与岩石强度和孔隙度发生强烈垂直变化的环境中的热液喷发危险情景相关。