Ashfall Load Thickness Conversion

Convert distinct dry ash layers and independently retained water into surface mass/weight load; dry bulk density includes pores, and structural capacity or collapse is not assessed.

Description

Ash thickness and dry bulk density determine dry mass loading.

Ash thickness and dry bulk density determine dry mass loading. Independently retained water adds mass before conversion to weight pressure.^[1]

Convert distinct dry ash layers and independently retained water into surface mass/weight load; dry bulk density includes pores, and structural capacity or collapse is not assessed.

When to use Ashfall Load Thickness Conversion

Use this tool to convert distinct dry ash layers and independently retained water into surface mass/weight load; dry bulk density includes pores, and structural capacity or collapse is not assessed.

Gather the relevant observations and fitted model parameters. Use the stated units and time basis; keep paired observations aligned.

How to use Ashfall Load Thickness Conversion and understand its results

Gather the relevant observations and fitted model parameters. Use the stated units and time basis; keep paired observations aligned.
Enter layerAshThicknessesMm, layerDryBulkDensitiesKgPerM3, retainedWaterKgPerM2, gravityMPerSecondSquared using the field table and calculation rules, then run the tool.
Read dryAshMassLoadingKgPerM2, wetMassLoadingKgPerM2, totalWeightLoadingPa. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
layerAshThicknessesMm	Layer ash thicknesses mm	list of number	Required
layerDryBulkDensitiesKgPerM3	Layer dry bulk densities kg per m3	list of number	Required
retainedWaterKgPerM2	Retained water kg per m2	number	Required
gravityMPerSecondSquared	Gravity m per second squared	number	Required

Align nonnegative layer thicknesses with positive dry bulk densities. Add nonnegative water kg/m² and apply positive gravity. Return dry and wet kg/m² and weight in pascals.^[2]

Paired lists must be nonempty and have equal lengths.

dry loading = Σ thicknessMm/1000 × dry density; weight = (dry loading + retained water) × gravity

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
dryAshMassLoadingKgPerM2	Dry ash mass loading kg per m2	number
wetMassLoadingKgPerM2	Wet mass loading kg per m2	number
totalWeightLoadingPa	Total weight loading Pa	number

json

{
  "input": {
    "layerAshThicknessesMm": [
      10,
      20
    ],
    "layerDryBulkDensitiesKgPerM3": [
      1000,
      500
    ],
    "retainedWaterKgPerM2": 5,
    "gravityMPerSecondSquared": 10
  },
  "output": {
    "dryAshMassLoadingKgPerM2": 20,
    "wetMassLoadingKgPerM2": 25,
    "totalWeightLoadingPa": 250
  }
}

Limitations and assumptions

Dry bulk density already includes pores; structural capacity is evaluated separately.

Numbers and computed results must be finite; overflow produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Roof Load Ash Collapse Risk Checker: Audit independently measured wet ash loads against caller remaining zone capacities and sum physical ash mass; capacities must account for other loads and this is not a collapse forecast or structural/access-safety certificate. For a complementary task, use Isomass Loading GM2 Contour Tool: Locate a target isomass contour by log loading versus square-root enclosed area; supplied areas require no coordinates, circular radius is an equivalent proxy, not a mapped boundary.

Further background: Volcanic ash loading on roofs.

References

Volcanic ash loading on roofs — USGS
Ashfall Load Thickness Conversion — tool.io

Similar or alternative tools

Roof Load Ash Collapse Risk Checker
Audit independently measured wet ash loads against caller remaining zone capacities and sum physical ash mass; capacities must account for other loads and this is not a collapse forecast or structural/access-safety certificate.
Isomass Loading GM2 Contour Tool
Locate a target isomass contour by log loading versus square-root enclosed area; supplied areas require no coordinates, circular radius is an equivalent proxy, not a mapped boundary.