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Assessing the risk of roof collapse in response to loading from volcanic ash with relevance to Ascension Island

Dr Mark Thomas (SEE), Dr Julia Crummy (BGS), Dr Antonio Abellan (SEE)

Contact email: m.e.thomas@leeds.acuk

Summary

The loading that results from ash fall following volcanic eruptions can pose a significant problem to the structural integrity of buildings.

Damage to buildings due to volcanic ash fall is frequently reported yet poorly studied. This is largely because damage data needs to be collected as soon as possible before clean-up, repair, or erosion by wind and rain. This involves entering areas where there is a danger of further eruptions, and there are often sensitivities with local communities, science agencies and disaster emergency managers. As a result, more focused experimental studies on the impacts of ash loading on buildings are needed, and given that over 800 million people are now estimated to live near active volcanoes, the evaluation of the vulnerability of buildings to ash loading is essential for disaster risk reduction.

Roof collapse is the result of a complex interaction involving the loading caused by the ash, the design and condition of the structure and the weather. As such there are three main objectives in this project.

1. Defining a “characteristic” amount of ash

2. Defining the relevant seasonal properties of the ash

3. Evaluating the vulnerability of buildings and the hazard posed.

The project objectives will be achieved through a combination of desk-, laboratory- and field-work. Attempting to undertake these objectives on a global scale is not possible, so this project will be using Ascension Island as a case study. Ascension Island is a remote volcanic island that lies ca. 90 km east of the Mid Atlantic Ridge in the South Atlantic. It rises 4 km from the seafloor to a height of 859 m above sea level (a.s.l.), and has an area of approximately 91 km2. It forms part of the UK Overseas Territory of St Helena, Ascension and Tristan da Cunha, and has a population of approximately 800 including the UK Royal Air Force and US Air Force. The island is volcanically active, with recent research revealing activity just a few hundred years old. Past volcanic activity on Ascension Island was dominated by mafic lava flows with felsic pyroclastic deposits and scoria. The explosive eruptive history is confined to vents on the central mountainous region of the island and recent research has revealed at least 74 pumice-producing eruptions were identified within the last 1 Myr.

The first stage of the project will be defining a “characteristic” value for the amount of ash. For ash fall, where eruptions can be separated by centuries, determining such a value is extremely challenging. In such situations, a scenario-based approach will be used, developed on the geological record. Multiple simulations are run for each scenario using a tephra dispersion model. For Ascension Island, explosive eruption scenarios have been developed and simulated based on two months of wind data. The resultant ash thickness maps have been used as a basis for an initial ash fall hazard assessment on Ascension Island at the BGS. This project will expand on this work through tephra dispersion modelling of a ten-year Reanalysis wind database to develop an ash loading characteristic value, and will be run with Dr Julia Crummy from the BGS as a leading member of the PhD supervisory team.

The second stage will involve characterising the ash and its interaction with the structures. To calculate the true load imposed on a roof there are many aspects that need to be considered. These include properties of the ash such as composition (density) and shape (related to the eruption style), whether the ash is dry or wet (which changes the density), or how the ash will have accumulated on the roof, which is determined by the shape of the roof and the material the roof is made from. Through laboratory work at the University of Leeds conducted on real and synthetic ash, this project will define the required properties and parameters.

Following the full probabilistic characterisation of the ash load, the third stage will involve incorporating these data into a vulnerability/hazard assessment for Ascension Island.

This project will benefit from extra funding and support from the BGS University Funding Initiative (BUFI). The additional funding (up to £11k) will help cover field work and any additional lab costs.

 

Click here for a full project description.

Related undergraduate subjects:

  • Civil engineering
  • Earth science
  • Engineering
  • Geological science
  • Geology
  • Geophysical science
  • Geophysics
  • Geoscience
  • Natural sciences
  • Physical geography