Collaborative Research: Understanding the Causes of Highly Explosive Basaltic Eruptions Using the AD 1085 Sunset Crater Eruption and its Deposits

在地球、火星、月球和金星上，被称为玄武岩的低粘度深色岩浆的喷发主导着火山活动。与黏性更强、挥发物更丰富的岩浆相比，玄武岩通常被认为具有较低的爆发潜力，只会产生影响相对较小地理区域的温和喷发。然而，玄武岩喷发表现出很大的可变性，从安静的熔岩流和轻微的爆炸到不太常见的大爆炸，形成30公里高的羽状物，将细火山灰分散到几百公里外。这些上端构件爆炸的确切原因在文献中有争议。在今天的美国，最近一次最大的单成因玄武岩火山喷发发生在900年前的日落火山口，位于亚利桑那州弗拉格斯塔夫东北约25公里处。火山喷发产生了熔岩流，但大部分喷发量是在至少8个爆炸阶段喷出的，产生了7公里到25公里高的喷发羽流，并在周围地区沉积了火山渣和火山灰毯。火山灰和火山灰厚度超过1厘米，覆盖了大约2300平方公里，影响了史前居民，导致人口流动，极大地改变了定居、生存、经济和仪式系统。火山喷发是该地区七个部落的口述传统。类似的现代火山爆发将严重影响美国西南部，造成商业和空中交通的严重中断。这个项目将检查日落火山口喷发，以检验解释异常大而剧烈的玄武岩喷发原因的假设。主要的假设是：a)岩浆特别富含挥发物，如水蒸气和二氧化碳，它们提供了驱动爆炸性喷发所需的能量；b)岩浆的黏度在浅层地下突然增加，这是由于岩浆放出气体和快速结晶，导致玄武岩紧紧地抓住气体，只有在到达地表时才以猛烈和爆炸性的方式释放它们。为了帮助确定这些过程在日落陨石坑的重要性，我们将首先通过沉积物的地层对比来确定熔岩流和喷发柱喷发的相对时间。火山渣结构（如气泡、晶体）将有助于揭示岩浆粘度，并提供后期喷发过程的信息，而对在更深处形成的晶体中被困的熔体包裹体的分析将提供有关初始岩浆挥发性含量的信息。

Eruption of low-viscosity, dark magma called basalt dominates volcanism on Earth, Mars, the Moon, and Venus. Compared to more viscous and more volatile-rich magmas, basalts are generally considered to have lower explosive potential, producing mild eruptions affecting relatively small geographical areas. Basaltic eruptions, however, display large variability and range from quiet lava flows and mild explosions to less common large explosions forming 30 km-high plumes that disperse fine ash up to several hundreds of kilometers. The exact causes of these upper end-member explosions are debated in the literature. The largest recent eruption of a monogenetic basaltic scoria-cone volcano in the present-day contiguous USA took place ~900 years ago at Sunset Crater, about 25 km NE of Flagstaff, AZ. The eruption produced lava flows, but most of the erupted volume was ejected during at least 8 explosive phases that produced eruption plumes from 7 km to 25 km high and deposited scoria and ash blankets over the surrounding area. Scoria and ash thicknesses greater than 1 cm cover approximately 2,300 km2 and impacted prehistoric inhabitants, leading to population movement and dramatically altered settlement, subsistence, economic, and ritual systems. The eruption figures in oral traditions of seven tribes in the area. A similar modern eruption would significantly affect the Southwest US, causing major disruption to commerce and air traffic.This project will examine the Sunset Crater eruption in order to test hypotheses explaining the causes of unusually large and violent basaltic eruptions. The leading hypotheses are a) the magma is especially rich in volatiles, such as water vapor and carbon dioxide, which provide the energy required to drive explosive eruptions and b) the magma viscosity abruptly increases in the shallow sub-surface due to magma outgassing and rapid crystallization, causing the basalt to hold its gases tightly, only to release them in a violent and explosive way upon reaching the surface. To help determine the importance of these processes at Sunset Crater, we will first determine the relative timing of the lava flow and eruption plume eruptions through stratigraphic correlation of the deposits. Scoria textures (e.g. bubbles, crystals) will help reveal magma viscosity and provide information on late-stage eruption processes, whereas analysis of melt inclusions trapped in crystals that formed at greater depths will provide information on initial magma volatile contents.