How rainfall influences tephra fall loading — an experimental approach

The load a tephra fall deposit applies to an underlying surface is a key factor controlling its potential to damage a wide range of assets including buildings, trees, crops and powerlines. Though it has long been recognised that loading can increase when deposits absorb rainfall, few efforts have be...

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Main Authors: Williams, George T., Jenkins, Susanna F., Lee, Daniel W. J., Wee, Shi Jun
Other Authors: Asian School of the Environment
Format: Article
Language:English
Published: 2021
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Online Access:https://hdl.handle.net/10356/153002
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spelling sg-ntu-dr.10356-1530022021-12-04T20:10:59Z How rainfall influences tephra fall loading — an experimental approach Williams, George T. Jenkins, Susanna F. Lee, Daniel W. J. Wee, Shi Jun Asian School of the Environment Earth Observatory of Singapore Science::Geology Ash Fall Hazard The load a tephra fall deposit applies to an underlying surface is a key factor controlling its potential to damage a wide range of assets including buildings, trees, crops and powerlines. Though it has long been recognised that loading can increase when deposits absorb rainfall, few efforts have been made to quantify likely load increases. This study builds on previous theoretical work, using an experimental approach to quantify change in load as a function of grainsize distribution, rainfall intensity and duration. A total of 20 laboratory experiments were carried out for ~ 10-cm thick, dry tephra deposits of varying grainsize and grading, taken to represent different eruptive scenarios (e.g. stable, waxing or waning plume). Tephra was deposited onto a 15° impermeable slope (representing a low pitch roof) and exposed to simulated heavy rainfalls of 35 and 70 mm h−1 for durations of up to 2 h. Across all experiments, the maximum load increases ranged from 18 to 30%. Larger increases occurred in fine-grained to medium-grained deposits or in inversely graded deposits, as these retained water more efficiently. The lowest increases occurred in normally graded deposits as rain was unable to infiltrate to the deposit’s base. In deposits composed entirely of coarse tephra, high drainage rates meant the amount of water absorbed was controlled by the deposit’s capillary porosity, rather than its total porosity, resulting in load increases that were smaller than expected. These results suggest that, for low pitch roofs, the maximum deposit load increase due to rainfall is around 30%, significantly lower than the oft-referenced 100%. To complement our experimental results, field measurements of tephra thickness should be supplemented with tephra loading measurements, wherever possible, especially when measurements are made at or near the site of observed damage. Ministry of Education (MOE) National Research Foundation (NRF) Published version This research was supported by the Earth Observatory of Singapore via its funding from the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative. 2021-10-28T08:36:18Z 2021-10-28T08:36:18Z 2021 Journal Article Williams, G. T., Jenkins, S. F., Lee, D. W. J. & Wee, S. J. (2021). How rainfall influences tephra fall loading — an experimental approach. Bulletin of Volcanology, 83(6), 42-. https://dx.doi.org/10.1007/s00445-021-01465-0 0258-8900 https://hdl.handle.net/10356/153002 10.1007/s00445-021-01465-0 2-s2.0-85107034573 6 83 42 en Bulletin of Volcanology 10.21979/N9/48FOZP © 2021 The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Science::Geology
Ash Fall
Hazard
spellingShingle Science::Geology
Ash Fall
Hazard
Williams, George T.
Jenkins, Susanna F.
Lee, Daniel W. J.
Wee, Shi Jun
How rainfall influences tephra fall loading — an experimental approach
description The load a tephra fall deposit applies to an underlying surface is a key factor controlling its potential to damage a wide range of assets including buildings, trees, crops and powerlines. Though it has long been recognised that loading can increase when deposits absorb rainfall, few efforts have been made to quantify likely load increases. This study builds on previous theoretical work, using an experimental approach to quantify change in load as a function of grainsize distribution, rainfall intensity and duration. A total of 20 laboratory experiments were carried out for ~ 10-cm thick, dry tephra deposits of varying grainsize and grading, taken to represent different eruptive scenarios (e.g. stable, waxing or waning plume). Tephra was deposited onto a 15° impermeable slope (representing a low pitch roof) and exposed to simulated heavy rainfalls of 35 and 70 mm h−1 for durations of up to 2 h. Across all experiments, the maximum load increases ranged from 18 to 30%. Larger increases occurred in fine-grained to medium-grained deposits or in inversely graded deposits, as these retained water more efficiently. The lowest increases occurred in normally graded deposits as rain was unable to infiltrate to the deposit’s base. In deposits composed entirely of coarse tephra, high drainage rates meant the amount of water absorbed was controlled by the deposit’s capillary porosity, rather than its total porosity, resulting in load increases that were smaller than expected. These results suggest that, for low pitch roofs, the maximum deposit load increase due to rainfall is around 30%, significantly lower than the oft-referenced 100%. To complement our experimental results, field measurements of tephra thickness should be supplemented with tephra loading measurements, wherever possible, especially when measurements are made at or near the site of observed damage.
author2 Asian School of the Environment
author_facet Asian School of the Environment
Williams, George T.
Jenkins, Susanna F.
Lee, Daniel W. J.
Wee, Shi Jun
format Article
author Williams, George T.
Jenkins, Susanna F.
Lee, Daniel W. J.
Wee, Shi Jun
author_sort Williams, George T.
title How rainfall influences tephra fall loading — an experimental approach
title_short How rainfall influences tephra fall loading — an experimental approach
title_full How rainfall influences tephra fall loading — an experimental approach
title_fullStr How rainfall influences tephra fall loading — an experimental approach
title_full_unstemmed How rainfall influences tephra fall loading — an experimental approach
title_sort how rainfall influences tephra fall loading — an experimental approach
publishDate 2021
url https://hdl.handle.net/10356/153002
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