Abstract Lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines. Spines are protrusions observed to extrude episodically during lava dome growth, yet the structural and mechanical factors controlling their formation are only partially understood. Here, we provide new, detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand-plaster mixtures from a fixed-diameter conduit under isothermal conditions. We trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process. Results show initial dome growth forming a steep-sided and flat-topped shape through extrusion of new material, leading to slumping of oversteepening slopes, forming a talus. Spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls, starting a cycle of spine growth and collapse. As our spines only appear after prolonged extrusion, we relate their appearance to the compaction and strengthening of material within the conduit. We find that spine diameter, height and volume are positively correlated with increasing cohesion and therefore material strength. The spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit, as shear extrusion occurs along vertical to outward-dipping fault planes. For natural domes, our findings imply that spine growth may be the consequence of compaction and densification via porosity loss, shearing and/or outgassing of conduit magma during ascent. More efficient compaction will yield wider and taller spines as a result of increasing rock strength. Our study further highlights the relevance of analogue experiments in the study of lava domes and spines, which remain one of the most hazardous and unpredictable features at dome-forming volcanoes worldwide.

中文翻译：

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使用模拟沙盒实验深入了解熔岩穹顶和脊柱挤压

摘要 熔岩穹顶的形成是层状火山的常见过程，涉及粘性熔岩的浅层侵入或挤压，并可能导致刺的隆起。刺是观察到在熔岩穹顶生长过程中不时地突出的突起，但控制其形成的结构和机械因素仅被部分了解。在这里，我们使用一组新的模拟实验，在等温条件下从固定直径的管道中挤出砂膏混合物，对熔岩穹顶的生长和刺的产生提供了新的、详细的见解。我们使用摄影测量方法跟踪位移和应变，以精确和详细地监控挤出过程。结果表明，最初的圆顶生长通过挤压新材料形成陡峭的平顶形状，导致过度陡峭的斜坡坍塌，形成距骨。发现脊椎在稍后阶段沿着源自管道壁的离散圆形断层穿过圆顶表面突出，开始脊椎生长和塌陷的循环。由于我们的刺只有在长时间挤压后才会出现，我们将它们的外观与管道内材料的压实和强化联系起来。我们发现脊柱直径、高度和体积与增加的内聚力和材料强度呈正相关。脊柱直径也被观察到小于或等于底层管道的直径，因为剪切挤压发生在垂直向外倾斜的断层面上。对于天然穹顶，我们的研究结果表明，脊柱生长可能是由于上升过程中导管岩浆的孔隙度损失、剪切和/或脱气导致的压实和致密化的结果。由于增加了岩石强度，更有效的压实将产生更宽更高的刺。我们的研究进一步强调了模拟实验在熔岩穹顶和刺研究中的相关性，这仍然是全球穹顶形成火山中最危险和最不可预测的特征之一。