Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, L69 3GP, UK.
Centre for Natural Hazards Research, Department of Earth Sciences, Simon Fraser University, Burnaby, BC, Canada.
Nat Commun. 2022 May 20;13(1):2832. doi: 10.1038/s41467-022-30501-6.
During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, chemical and textural observations, coupled with high temperature rheometry and thermal modelling, reveal that abrupt transitions in eruptive behaviour - from lava fountaining to low-energy bubble bursts - created these pyroclastic deposits. These findings should help identify transitions in eruptive behaviour at other mafic volcanoes worldwide.
在低粘度岩浆的爆发性喷发中，火山碎屑岩主要通过强制对流冷却。根据冷却效率与其他时间尺度的关系，可以形成一系列沉积物。高于玻璃化转变温度的热碎屑的沉积可以形成飞溅丘、堤堰和碎屑熔岩流。碎屑也可以冷沉积，形成火山灰锥和毯子。因此，沉积物和火山碎屑岩的类型可以提供有关喷发动力学和岩浆性质的信息。在这里，我们研究了来自加拿大不列颠哥伦比亚省的 Tseax 火山的火山碎屑岩。这些新确定的膨胀火山碎屑岩呈流状，经历了沉积后膨胀，并与火山渣并列。详细的野外、化学和结构观察，加上高温流变学和热模拟，揭示了喷发行为的突然转变——从熔岩喷泉到低能量气泡爆裂——导致了这些火山碎屑沉积物的形成。这些发现应该有助于识别世界各地其他镁铁质火山的喷发行为转变。
