Violent Basaltic Explosive Volcanism: A Case Study Of The 1886 Tarawera Eruption, New Zealand

摘要：玄武岩火山活动通常被认为是产生熔岩的渗出物，其最具爆炸性的表现形式从温和的斯特龙堡式活动到更猛烈的火喷泉喷发。然而，一些玄武岩喷发现在被认为是非常猛烈的，即产生广泛的呼吸岩浆、下普林尼期和普林尼期跌落矿床。这些喷发特别危险，因为玄武岩岩浆在喷发前的上升速度非常快（发出警告的时间短至几小时），而且它们的前兆可能被忽视或误解。这一提议解决的主要问题是：是什么条件导致玄武岩岩浆采用一种更典型的化学演化的高粘性岩浆喷发方式？可能的机制（单独作用或协同作用）有：(1)岩浆和水之间的相互作用；（ii）非常快速的上升导致脱气的延迟发生，然后在管道的浅层产生异常快速的“失控”囊泡；（iii）上升过程中岩浆的微岩结晶和脱气导致粘度增加。我们的目标是建立1886年塔拉韦拉火山爆发的普林尼期的触发机制。这一建议将验证一种假设，即这一阶段是岩浆上升过程中流变学变化的结果，这种变化伴随着早期（破碎前）玄武岩熔体与形成导管壁的含水流纹岩单元之间的相互作用，或者是后期岩浆-水相互作用。

AbstractEAR-0125719HoughtonUniversity of HawaiiBasaltic volcanism is most typically thought to produce effusion of lava, with the most explosive manifestations ranging from mild Strombolian activity to more energetic fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e. generating widespread phreatomagmatic, subplinian and Plinian fall deposits. These eruptions are particularly dangerous because the ascent rate of basaltic magma prior to eruption can be very rapid (giving warning times as little as a few hours) and because their precursors may be ignored or misunderstood. The main question addressed in this proposal is: what are the conditions that cause basaltic magma to adopt an eruption style more typical of chemically evolved, highly viscous magma? Possible mechanisms (acting singly, or in concert) are: (1) interaction between magma and water, (ii) very rapid ascent producing a delayed onset of degassing then exceptionally rapid "runaway" vesiculation at shallow levels in the conduit, (iii) microlite crystallization and degassing of the magma during ascent leading to increased viscosity. Our goal is to establish the triggering mechanism for the Plinian phase of the 1886 Tarawera eruption. This proposal will test the hypothesis that this phase was a consequence of either rheologic changes during magma ascent that accompanied early (pre-fragmentation) interaction between the basaltic melt and water-bearing rhyolitic units forming the conduit walls or late-stage magma water interaction.