Unsaturated Volcanic Tephra and Its Effect for Soil Movement in El Salvador

Chávez, José A.

doi:10.11648/j.earth.20130202.15

Cited by 1 publication

(1 citation statement)

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“…The dashed line marks average values for the total porosity of typical alluvium deposits from Stephens et al (1998), showing that the total porosities of granular sedimentary deposits follow the opposite trend of total porosities in tephra deposits. All studies in the figure have been referenced within the text with the exception of Diaz et al (2005) and Hernández (2013) eruptions could increase roof collapse probabilities by an average of 10% at Vulcano Island (i.e. half of all buildings exposed to tephra had a 20% chance of collapse under dry conditions, and this increased to a 30% chance with the addition of 20 mm of rainfall).…”

Section: Implications For Damage Assessmentmentioning

confidence: 99%

How rainfall influences tephra fall loading — an experimental approach

et al. 2021

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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.

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Section: Implications For Damage Assessmentmentioning

confidence: 99%