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

合作研究：利用公元 1085 年日落火山口喷发及其沉积物了解高爆炸性玄武岩喷发的原因

• 批准号: 1322081
• 负责人: Michael Ort
• 金额: $ 12万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322081&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; Causes; Highly

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.

被称为玄武岩的低粘度深色岩浆喷发主导着地球、火星、月球和金星上的火山活动。与粘度更高、挥发性更丰富的岩浆相比，玄武岩通常被认为具有较低的爆炸潜力，会产生轻微的喷发，影响相对较小的地理区域。然而，玄武岩喷发表现出很大的变异性，范围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公里高的羽流，将细火山灰分散到数百公里处。这些上端构件爆炸的确切原因在文献中有争论。最近最大的一次火山喷发发生在大约900年前，位于亚利桑那州弗拉格斯塔夫东北约25公里处的日落陨石坑，是今天美国毗邻的一座单一成因的玄武岩火山锥火山。这次喷发产生了熔岩流，但大部分喷发量是在至少8个爆炸阶段被喷射出来的，这些阶段产生了从7公里到25公里高的喷发羽流，并在周围地区沉积了焦炭和火山灰。超过1厘米的渣土和火山灰覆盖了大约2300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、生存、经济和仪式制度。喷发出现在该地区七个部落的口头传统中。类似的现代火山喷发将严重影响美国西南部，对商业和空中交通造成重大干扰。该项目将研究日落陨石坑喷发，以测试解释异常巨大和猛烈的玄武岩喷发原因的假说。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，提供驱动爆炸性喷发所需的能量；b)由于岩浆放气和快速结晶，岩浆在浅层次表层突然增加粘度，导致玄武岩紧紧抓住气体，但到达地表后以猛烈和爆炸性的方式释放出来。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羽流的相对时间。珊瑚结构(如气泡、晶体)将有助于揭示岩浆粘度，并提供有关后期喷发过程的信息，而对在更深处形成的晶体中捕获的熔融包裹体的分析将提供有关岩浆初始挥发性含量的信息。