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

地球、火星、月球和金星上的火山活动主要是由称为玄武岩的低粘度黑色岩浆喷发而成。与更粘稠和更富挥发性的岩浆相比，玄武岩通常被认为具有较低的爆炸潜力，产生影响相对较小地理区域的温和喷发。然而，玄武岩喷发显示出很大的可变性，从安静的熔岩流和温和的爆炸到不太常见的大爆炸，形成30公里高的羽状物，将细灰分散到数百公里。 这些上端元爆炸的确切原因在文献中有争议。最近最大的一次单成因玄武岩火山渣锥火山喷发发生在今天美国连续约900年前在日落火山口，约25公里东北的弗拉格斯塔夫，亚利桑那州。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，这些阶段产生了7公里至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层。厚度超过1厘米的火山渣和火山灰覆盖了大约2，300平方公里，影响了史前居民，导致人口迁移，并极大地改变了定居点，生计，经济和仪式系统。 火山爆发的数字在该地区的七个部落的口头传统。类似的现代火山爆发将显著影响美国西南部，造成商业和空中交通的重大中断。本项目将研究日落火山口喷发，以测试解释异常大而猛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，这些挥发物提供了驱动爆炸性喷发所需的能量; B）由于岩浆的脱气和快速结晶，岩浆的粘性在浅地表下突然增加，导致玄武岩紧紧地保持其气体，只有在到达地表时才以暴力和爆炸性的方式释放它们。为了帮助确定这些过程在日落火山口的重要性，我们将首先通过沉积物的地层对比来确定熔岩流和喷发羽流喷发的相对时间。 火山渣的结构（如气泡，晶体）将有助于揭示岩浆粘度，并提供信息的后期喷发过程中，而在更深的深度形成的晶体中捕获的熔融包裹体的分析将提供信息的初始岩浆挥发性成分。

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.