Evolution of magma decompression and discharge during a Plinian event (Late Bronze-Age eruption, Santorini) from multiple eruption-intensity proxies
Evolution of magma decompression and discharge during a Plinian event (Late Bronze-Age eruption, Santorini) from multiple eruption-intensity proxies
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来自多个喷发强度代理的普林尼事件（青铜时代晚期喷发，圣托里尼岛）期间岩浆减压和喷发的演变
DOI：
10.1007/s00445-021-01438-3
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发表时间：
2021
影响因子：
3.5
通讯作者：
Flaherty, Taya
中科院分区：
文献类型：
--
作者：
Myers, Madison L.;Druitt, Timothy H.;Schiavi, Federica;Gurioli, Lucia;Flaherty, Taya
本文采用三种独立的方法对圣托里尼火山晚青铜时代喷发的亚普林尼期和普林尼期喷发强度的时间演化进行了研究。(1)采用方法2和方法3对同一套火山碎屑进行测量，根据新的岩屑等面图对多层落岩进行大规模喷发速率计算；(2)根据囊泡数密度计算岩浆减压速率；(3)根据熔体再入物的H2O梯度计算岩浆减压速率。喷发速率增加了两个数量级，在普林尼期高峰期达到210 × 106kg s−1（羽高28.4±1.0 km）；在第一代火山碎屑涌流之后，它在沉降物安置的最后阶段下降了。假设囊泡非均质成核（2 ~ 19 MPa s - 1），熔体再入的减压速率（0.008 ~ 0.25 MPa s - 1）比囊泡数密度的减压速率低2 ~ 3个数量级。熔体再入被认为记录了深部输水管道的缓慢减压，而由于与岩浆泡化和破碎相关的陡峭的非线性压力梯度，囊泡在浅层管道中记录了更高的减压速率。向上汇聚的流动从堤状的深导管流向更圆柱形的浅导管，也可能在导致向上加速流动方面发挥了作用。熔体再入体记录的深度减压速率变化与团块喷发速率无关，而小泡记录的深度减压速率变化介于两者之间。考虑到从非定常到稳定的普林尼火山喷发，这可能反映了随着普林尼火山喷发的进行，由于深补给堤的加宽和延长，导管系统中存在瞬态流动条件。随着岩浆体喷发速率达到峰值，岩浆应变速率和减压速率增加，导管内破碎程度下降。
We have coupled three independent methods to investigate the time evolution of eruptive intensity during the sub-Plinian and Plinian phases of the 3600-year BP Late Bronze-Age eruption of Santorini Volcano: (1) mass eruption rate based on new lithic isopleth maps for multiple layers of the fall deposit, (2) magma decompression rate calculated from vesicle number densities, and (3) magma decompression rate calculated from H2O gradients in melt reentrants, with methods 2 and 3 measured on the same suite of pyroclasts. Mass eruption rate increased by two orders of magnitude, reaching 210 × 106kg s−1at the peak of the Plinian phase (plume height 28.4 ± 1.0 km); it then declined in the final stage of fallout emplacement following the first generation of pyroclastic surges. Decompression rates from melt reentrants (0.008 to 0.25 MPa s−1) are two to three orders of magnitude lower than those from vesicle number densities, assuming heterogeneous vesicle nucleation (2 to 19 MPa s−1). Melt reentrants are thought to record slow decompression in the deep feeder conduit, whereas vesicles record much higher rates of decompression in the shallow conduit due to the steep, nonlinear pressure gradients associated with magma vesiculation and fragmentation. Upwardly converging flow from a dike-like, deep conduit to a more cylindrical, shallow conduit may also have played a role in causing upwardly accelerating flow. Variations in deep decompression rate recorded by melt reentrants are decoupled from mass eruption rate, whereas those recorded by vesicles lie in between. Taken with the transition from unsteady to steady Plinian eruption, this may reflect the existence of transient flow conditions in the conduit system due to widening and lengthening of a deep feeder dike as Plinian eruption progressed. As the mass eruption rate rose to its peak value, the fragmentation level fell in the conduit due to increasing rates of magma strain and decompression.
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