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.

低粘性的喷发，被称为玄武岩的深色岩浆主导着地球，火星，月球和金星的火山主义。与更具粘性和更挥发性的岩浆相比，玄武岩通常被认为具有较低的爆炸潜力，从而产生轻度的喷发，影响相对较小的地理区域。然而，玄武岩爆发显示出很大的可变性，从安静的熔岩流和轻度爆炸到不常见的大型爆炸，形成了30公里高的羽毛，可将细灰分散在高达几百公里的地方。 这些高端成员爆炸的确切原因在文献中进行了辩论。当今美国，一座单基因玄武岩菌孔火山的最大爆发发生在大约900年前，在亚利桑那州弗拉格斯塔夫（Flagstaff）约25公里的日落火山口。喷发产生了熔岩流，但大部分喷发的体积在至少8个爆炸阶段被弹出，这些爆炸阶段产生了从7 km到25 km高的喷发羽，并在周围地区沉积的Scoria和Ash毯子。大于1厘米的Scoria和Ash厚度覆盖约2300 km2，并影响了史前居民，从而导致人口运动并发生了巨大变化，定居点，生存，经济和礼节系统。 该地区七个部落的口头传统的喷发数字。类似的现代喷发会显着影响美国西南部，从而导致商业和空中交通的重大破坏。该项目将检查日落火山口爆发，以检验假设，解释了异常大型和暴力的底层爆发的原因。主要假设是a）岩浆特别丰富的挥发物，例如水蒸气和二氧化碳，提供了驱动爆炸性爆发所需的能量，b）岩浆粘度突然增加，由于岩浆的浅层层次表面造成的浅层降压和快速结晶而造成了底部，使其仅在其范围内散发出来，从而使其仅释放出来，并释放出来，并释放出来，并释放出来，并释放出来，并释放出来。为了帮助确定日落火山口的这些过程的重要性，我们将首先确定熔岩流和喷发羽流的相对时机通过沉积物的地层相关性。 Scoria纹理（例如气泡，晶体）将有助于揭示岩浆粘度并提供有关晚期喷发过程的信息，而对捕获在更深入的晶体中的熔体夹杂物的分析将提供有关初始岩浆挥发物含量的信息。