Phreatoplinian eruptions: Mechanisms derived from comparative case studies

从富含浮石、分选良好的正常普林期沉积，到异常富含岩屑和/或细粒(可能是影响喷发的水的证据)的浮石沉积，到所谓的深成沉积(可能是近端的细粒浮石(可能是水冲沉积的证据))，范围从富含浮石、分选良好的正常普林斯沉积到所谓的深成沉积(可能是水冲沉积的证据)，但含有高度泡孔的浮石，岩屑贫乏。这里研究的三个特夫拉包含了跨越整个山脉的沉积物：刚果特夫拉、康卡斯特特弗拉和洛斯乔科斯特弗拉。在确定了项目第一阶段的内部地层、分布、岩性和地球化学成分以及固有的岩浆参数后，第二阶段将侧重于更详细地研究颗粒大小和形状以及浮石泡囊结构，以便更好地约束岩浆脱气、与管道中外部水的接触以及在破碎和喷发过程中与地表外部水相互作用的相对作用。

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.