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

在我们较大的火山中，短暂但剧烈的爆发事件经常发生在长期形成熔岩的喷发中。类似的火山爆发也发生在1991年的皮纳图博火山爆发之前。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。这些火山爆发几乎没有预警信号，但却影响了附近人口众多、不断增长的地区。这项研究的新颖之处在于，它关注的是1912年发生在阿拉斯加诺瓦鲁普塔火山（Novarupta）的一次研究非常充分的事件，这是过去100年来最大的一次爆发。三次强大的喷发脉冲持续了大约60个小时，随后是一系列剧烈的、短暂的爆炸，喷出的岩浆块显示出不同的岩浆结构。这些纹理形成了导致火山活动方式变化的过程的“指纹”。该项目使用了各种新开发的技术来捕捉火山管道系统浅层部分气体释放和逃逸过程的速率。这些技术的共同之处在于，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。它们包括囊泡的二维和三维成像，即喷发物质中的气泡，以及块体中残余气体和渗透性的测量。本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转变为一系列短暂的不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、莱斯大学、萨瓦大学和法国奥尔海姆斯大学之间的材料、学生和思想交流。两项新的倡议，学生到学校和教师到实地，旨在与学校教师和班级进行接触和对话，以激励高中生在他们的本科课程中考虑将地球科学作为研究领域。

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.