71 Gulch Volcano, located in the western Snake River Plain, southwestern Idaho (USA), was formed by a basaltic fissure eruption into Pliocene Lake Idaho. Deposits at and below the eruptive surface record the nature of explosive and non-explosive sediment-magma and water-magma interactions. The paleoenvironment and the volcanic plumbing system of 71 Gulch eruption were reconstructed from a detailed study of the now-exposed eruptive and subsurface deposits. Estimated water levels during the eruption range from 1 to 53 m across the entire volcano based on the distribution of pillow lavas. Billowed dikes and fluidal peperites are two types of intrusive features found ≤ 12 m below the syn-eruptive surface that have similar continuous margins representing ductile behavior and emplacement into soft, deformable sediment. In comparison, tabular dikes and blocky peperites occur throughout 41 m thick of exposed deposits below the syn-eruptive surface. A conical, diatreme-like vent structure dominates the subsurface exposure, indicating excavation by phreatomagmatic explosions. Localized spatter within the main subsurface vent suggests temporary exclusion of water and thus a period of brief vent growth above the lake level. Evidence of sediment-magma mingling through blocky and fluidal peperites shows how differing subsurface depths impact the resulting mingling textures.

中文翻译：

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71峡谷玄武岩岩浆裂隙第1部分：沉积岩浆混合和喷发行为

71 峡谷火山，位于美国爱达荷州西南部蛇河平原西部，由玄武岩裂隙喷发进入爱达荷州上新世湖而形成。喷发面及其下方的沉积物记录了爆炸性和非爆炸性沉积物-岩浆和水-岩浆相互作用的性质。通过对现已暴露的喷发和地下沉积物的详细研究，重建了 71 次峡谷喷发的古环境和火山管道系统。根据枕状熔岩的分布，估计整个火山喷发期间的水位范围为 1 至 53 m。翻滚岩脉和流体火山岩是在同喷发表面以下≤ 12 m 处发现的两种侵入特征，它们具有类似的连续边缘，代表韧性行为和侵位到柔软、可变形的沉积物中。相比下，在同喷发表面以下 41 m 厚的裸露沉积物中，出现了板状岩脉和块状 peperite。一个圆锥形的、类似火山口的喷口结构在地下暴露中占主导地位，表明是由潜水岩浆爆炸进行的挖掘。主要地下喷口内的局部飞溅表明暂时没有水，因此在湖面上方有一段短暂的喷口生长。沉积物-岩浆通过块状和流态珍珠岩混合的证据表明不同的地下深度如何影响由此产生的混合结构。主要地下喷口内的局部飞溅表明暂时没有水，因此在湖面上方有一段短暂的喷口生长。沉积物-岩浆通过块状和流态珍珠岩混合的证据表明不同的地下深度如何影响由此产生的混合结构。主要地下喷口内的局部飞溅表明暂时没有水，因此在湖面上方有一段短暂的喷口生长。沉积物-岩浆通过块状和流态珍珠岩混合的证据表明不同的地下深度如何影响由此产生的混合结构。