Phreatoplinian eruptions: Mechanisms derived from comparative case studies

广泛的普林尼期扩散的沉降体及其相关的流动沉积物，范围从富含浮石、分选良好的正常普林尼期沉积物，到那些异常富含岩屑和/或细颗粒的沉积物（可能是水影响喷发的证据），再到那些被称为潜水普林尼期的沉积物，这些沉积物的近端甚至是细颗粒的（可能是水冲刷沉积的证据），但含有高度水疱状的浮石，岩石含量很少。这里研究的三个tephras包含了横跨整个范围的沉积物：刚果Tephra， Conacaste Tephra和Los chocoyoos Tephra。在一期工程确定了其内部地层、分布、岩性和地球化学组成以及固有岩浆参数后，二期工程将重点对其粒度和形状以及浮石泡化结构进行更详细的研究，以更好地约束岩浆脱气、管道内与外部水接触、以及在破碎和喷发过程中与地表外部水的相互作用。

Fallout tephras of widespread Plinian dispersal, and their associated flow deposits, range from pumice-rich, well-sorted normal Plinian deposits through those that are unusually lithic-rich and/or fine-grained (possible evidence for water affecting the eruption) to those called phreatoplinian, which are fine-grained even proximally (possible evidence of water-flushed sedimentation) but contain highly vesicular pumice and are poor in lithics. The three tephras studied here contain deposits spanning the whole range: the Congo Tephra, the Conacaste Tephra, and the Los Chocoyos Tephra. Having determined their internal stratigraphies, distribution, lithological and geochemical composition as well as inherent magmatic parameters in the first phase of the project, this second phase will focus on more detailed studies of grain size and shape as well as pumice vesiculation textures in order to better constrain the relative roles of magmatic degassing, contact to external water in the conduit, and interaction with external water at the surface in the fragmentation and eruption processes.