Ending a Powerful Explosive Eruption: The Case Study of Novarupta 1912, Alaska

在我们较大的火山中，短暂但猛烈的爆炸性事件经常发生在长期形成熔岩的喷发期间。类似的喷发也发生在1991年皮纳图博火山强大而稳定的喷发之前或结束时。在过去的10年里，至少有24次这样的喷发发生在12个不同的国家。这些喷发几乎没有警告信号，但却影响了附近人口众多且不断增长的地区。这项研究的新奇之处在于，它关注的是1912年阿拉斯加州诺瓦鲁塔火山发生的一次特别深入的研究，这是近100年来最大的一次喷发。在大约60个小时的时间里，发生了三次强烈的喷发脉冲，随后是一系列猛烈的、短暂的爆炸，喷出的岩块显示出各种岩浆结构。这些纹理形成了导致火山活动方式变化的过程的“指纹”。该项目使用各种新开发的技术来捕捉火山管道系统浅层气体释放和泄漏的速度。这些技术的共同点是，它们都是在毫米到微米的尺度上对喷发物质的特征进行微观分析。它们包括对气泡(即喷发物质中的气泡)的2D和3D成像，以及对块体中残留气体和渗透率的测量。这项研究的中心目标是重建浅层岩浆管道的结构，并限制导致从强大的稳定喷发方式过渡到一系列短暂的非稳定脉冲爆炸的条件。该项目将涉及夏威夷大学马诺阿分校、加州大学伯克利分校和莱斯大学与萨瓦大学和法国奥莱斯大学之间的材料、学生和思想交流。两项新的倡议，学生到学校和实地教师，旨在与学校教师和班级进行联系和对话，以激励高中生将地球科学作为他们本科课程的一个学习领域。

Short-lived but violent explosive episodes frequently occur during long-lived lava-forming eruptions at our larger volcanoes. Similar eruptions also occur during the build-up to or wind-down from powerful steady eruptions as seen at Mount Pinatubo in 1991. At least 24 such eruptions have occurred in the last 10 years in 12 different countries. These eruptions had few warning signs but yet impacted nearby regions with large, growing populations. The novelty of this study is its focus on an exceptionally well-studied event at Novarupta volcano, Alaska in 1912, which was the largest explosive eruption in the last 100 years. Three powerful eruption pulses, over approximately 60 hours, were followed by a series of violent, short explosions ejecting blocks showing a diverse range of magma textures. These textures form 'fingerprints' to the processes that caused the change in style of activity at the volcano. The project uses a variety of newly developed techniques to capture the rates of processes of gas release and escape in the shallow portions of the volcano's plumbing system. The techniques have in common that they are microanalysis of features of the erupted material on scales of millimeters to micrometers. They include 2D and 3D imaging of vesicles, i.e., the gas bubbles in the erupted material, and measurement of the residual gases in and the permeability of the blocks. The central aim of this study is to reconstruct the architecture of the shallow magma plumbing, and constrain the conditions that led to a transition from a powerful steady eruption style into a series of short unsteady pulsing explosions.The project will involve exchange of material, students and ideas between University of Hawaii at Manoa, University of California at Berkeley and Rice University with Université de Savoie, and Université d'Orléans, in France. Two new initiatives, Students to Schools and Teachers in the Field, are aimed at contact and dialog with school teachers and classes to motivate high school students to consider the earth sciences as a field of study in their undergraduate program.