Development and analysis of a database of volcanic ash layers from ocean drilling cores as a record of global explosive volcanism

作为全球爆发性火山活动记录的海洋钻探岩心火山灰层数据库的开发和分析

• 批准号: NE/I006125/1
• 负责人: Robert Sparks
• 金额: $ 42.14万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FI006125%2F1
• 关键词: Development; analysis; database; volcanic; ash

Volcanism is the most dramatic manifestation that we live on a dynamic planet. Volcanoes are a key part of the Earth System and the major way in which many chemicals are recycled from the Earth's interior to the surface. Eruptions can be very violent and a cause of disasters. It is of fundamental interest to understand what controls the size of volcanic eruptions, the rates of volcanic activity and how size and frequency vary with time. The most comprehensive source of information on global volcanism is from the cores collected from the deep sea by the ocean drilling programme. Everytime there is a large eruption volcanic ash is blown by the wind and deposited on the sea floor to form a distinctive layer which can extend hundreds to thousands of kilometres from the volcano. These layers can be studied in the hundreds of cores collected around the World since the Ocean Drilling Programme began in 1968. This project will for the first time create a database of volcanic ash layers. Information that will be included in the database will be the thicckness of the ash layer, age of the eruption and location of the volcano. It is however not simple to use this information. Intuitively a thick ash layer in a core over 1000 kilometres from the volcano is likely caused by a very big eruption, but how big? Also a sequence of ash layers in a core must give some information about the frequency of these very big eruptions, but can this be quantified? The project aims to do more than just saying from the eruption that the eruption was very big or that the several very big eruptions every million years or so from an area of volcanism. To extract more exact information requires development and application of models that describe the processes of eruption, transport of volcanic ash in the atmosphere and settling of fine ash to deposit on the ocean floor. The size of a volcanic eruption is measured by the mass of ash erupted. The greater the mass of ash the thicker the deposit is likely to be at a given place on the sea floor. However it is not just the size that matters. The ash will be thicker in the direction that the wind blows and may not even deposit at all in some areas if the wind is not in the right direction. Intensity of an eruption is the mass erupted per unit time/ more intense eruptions push ash higher in the atmosphere and results in the ash being spread over a greater area. The thickness also depends on the range of sizes of the ash particles. Eruptions that produce finer ash will tend to have the ash spread much further. These and other controls on ash thickness are uncertain and also can vary independently. Thus many different combinations of these controls may result in the same ash thickness. With a computer it is nowadays possible to find out all variations of processes and parameters that can lead to the same ash thickness. Thus magnitude of the eruption can be deduced, but will be a range rather than an exact number. The same approach can be applied also to constrain rates of volcanism and again the result will be a range of values. With ocean drilling cores this is somewhat complicated by the movement of the tectonic plates which commonly moves sites towards the volcanoes, bu this effect can be taken into account in models With these ranges of values of eruption size and frequency we can use statistical techniques to deduce some fundamental questions about volcanism on earth over the many millions of years. What does the frequency of eruptions vary with size? On the whole we expect like earthquakes that the bigger eruptions are less common than smaller ones, but what is this relationship? The frequencies of small eruptions can be inferred from historical records, but the ash layers in the cores are much better source to deduce the rarer big events. Have the rates of volcanism changed with time and have the locations of actiove volcanoes changed? How can we explain these changes?

火山活动是我们生活在一个充满活力的星球上的最戏剧性的表现。火山是地球系统的重要组成部分，也是许多化学物质从地球内部循环到地表的主要途径。火山爆发可能非常猛烈，是造成灾难的原因。了解是什么控制着火山爆发的规模、火山活动的速率以及规模和频率如何随时间变化具有根本意义。关于全球火山活动的最全面的信息来源是海洋钻探方案从深海收集的岩心。每次大规模喷发，火山灰被风吹到海底，形成一个独特的层，可以从火山延伸数百到数千公里。自1968年海洋钻探计划开始以来，这些地层可以在世界各地收集的数百个岩心中进行研究。该项目将首次建立火山灰层数据库。数据库将包括火山灰层的厚度、喷发的年龄和火山的位置。然而，使用这些信息并不容易。直觉上，距离火山1000多公里的火山核心中的厚厚的灰层可能是由一次非常大的喷发造成的，但是有多大呢？同时，一个地核中的一系列火山灰层也一定提供了一些关于这些大喷发频率的信息，但这能量化吗？该项目的目的不仅仅是从火山爆发中说火山爆发非常大，或者每百万年左右从火山活动区域发生几次非常大的火山爆发。为了获得更准确的资料，需要发展和应用各种模型，以描述火山爆发、火山灰在大气中的迁移以及细灰沉降到洋底的存款过程。火山爆发的规模是由喷发出的火山灰的质量来衡量的。火山灰的质量越大，海底某一特定地点的存款就可能越厚。然而，重要的不仅仅是规模。在风吹的方向上，火山灰会更厚，如果风的方向不对，在某些地区甚至可能根本没有存款。喷发强度是单位时间内喷发的质量/更强烈的喷发会将火山灰推到大气中更高的位置，导致火山灰扩散到更大的区域。厚度还取决于灰颗粒的尺寸范围。火山喷发产生的火山灰较细，往往会使火山灰扩散得更远。这些和其他控制灰厚度是不确定的，也可以独立变化。因此，这些控制的许多不同组合可导致相同的灰厚度。如今，使用计算机可以找出所有可能导致相同灰厚的工艺和参数的变化。因此，可以推断出喷发的规模，但这只是一个范围，而不是一个确切的数字。同样的方法也可以应用于限制火山活动的速率，其结果将是一系列的值。对于海洋钻探岩心，由于构造板块的运动，这一点有些复杂，通常会将地点移向火山，但是这种影响可以在模型中考虑进去。根据这些喷发规模和频率的值范围，我们可以使用统计技术来推断地球上数百万年来火山活动的一些基本问题。火山爆发的频率随规模的不同而变化？总的来说，我们像地震一样，认为较大的火山爆发比较小的火山爆发更不常见，但这种关系是什么？小规模喷发的频率可以从历史记录中推断出来，但火山岩芯中的火山灰层是推断更罕见的大事件的更好来源。火山活动的速率是否随时间而改变？活火山的位置是否改变？我们如何解释这些变化？

项目成果

Quantifying uncertainties in marine volcanic ash layer records from ocean drilling cores

• DOI: 10.1016/j.margeo.2014.08.010
• 发表时间: 2014-11-01
• 期刊: MARINE GEOLOGY
• 影响因子: 2.9
• 作者: Mahony, Sue H.;Sparks, R. S. J.;Barnard, Nick H.
• 通讯作者: Barnard, Nick H.

Increased rates of large-magnitude explosive eruptions in Japan in the late Neogene and Quaternary.

• DOI: 10.1002/2016gc006362
• 发表时间: 2016-07
• 期刊: GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
• 影响因子: 3.5
• 作者: Mahony, S. H.;Sparks, R. S. J.;Wallace, L. M.;Engwell, S. L.;Scourse, E. M.;Barnard, N. H.;Kandlbauer, J.;Brown, S. K.
• 通讯作者: Brown, S. K.