Basal Shear Stress

Calculate local slab driving and shape-corrected basal shear; longitudinal stress gradients and spatial force balance are excluded.

Description

A local slab model estimates glacier driving stress from thickness and surface slope.

A local slab model estimates glacier driving stress from thickness and surface slope. A valley factor supplies a simplified correction to basal shear.^[1]

Calculate local slab driving and shape-corrected basal shear; longitudinal stress gradients and spatial force balance are excluded.

When to use Basal Shear Stress

Use this for the following task: Calculate local slab driving and shape-corrected basal shear; longitudinal stress gradients and spatial force balance are excluded.

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.

How to use Basal Shear Stress and understand its results

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.
Enter iceDensityKgPerM3, gravityMPerSecondSquared, iceThicknessM, surfaceSlopeDegrees, valleyShapeFactor using the field table, then run the tool.
Read uncorrectedDrivingStressPa, shapeCorrectedBasalStressPa. Interpret flags, units, ordering and placeholder values using the rules below.
Review any reported issue or failed check, correct the supplied values when appropriate, and verify the result in its intended context.

Input field	Meaning	Value type and bounds	Requirement
iceDensityKgPerM3	Ice density kg per m3	number	Required
gravityMPerSecondSquared	Gravity m per second squared	number	Required
iceThicknessM	Ice thickness m	number	Required
surfaceSlopeDegrees	Surface slope degrees	number	Required
valleyShapeFactor	Valley shape factor	number	Required

Require positive thickness/density/gravity, shape factor in (0,1] and slope in [0,90). Convert degrees before evaluating the sine.^[2]

driving = ρgH sin(slopeDegrees); corrected = driving × shapeFactor

This summarizes the declared operation. Units, indexing, inclusivity and exceptional cases are explained in the surrounding text.

Output field	Meaning	Value type
uncorrectedDrivingStressPa	Uncorrected driving stress pa	number
shapeCorrectedBasalStressPa	Shape corrected basal stress pa	number

json

{
  "input": {
    "iceDensityKgPerM3": 900,
    "gravityMPerSecondSquared": 10,
    "iceThicknessM": 100,
    "surfaceSlopeDegrees": 30,
    "valleyShapeFactor": 0.8
  },
  "output": {
    "uncorrectedDrivingStressPa": 449999.99999999994,
    "shapeCorrectedBasalStressPa": 360000
  }
}

Limitations and assumptions

Longitudinal stress gradients and a complete force balance are excluded. Zero slope is valid here and returns zero stress.

Constants and empirical coefficients are supplied rather than calibrated. Check units and observational applicability before interpreting the model. Malformed requests produce input errors. A successfully evaluated request can still contain false flags, empty result lists or a result outside the supplied threshold; those outcomes have the meanings stated above.

Alternative or Complementary methods

Choose Thickness From Slope Driving Stress for this operation: Invert local shape-corrected slab driving stress for ice thickness; flat-slope inversions are undefined, and longitudinal stresses remain excluded. For a complementary task, use Shape Factor Valley Correction for this operation: Estimate valley shape factor A/(P·H) from a flat-surface piecewise-linear bed section; not inversion from basal stress or a universal valley correction.

Further background: Ice rheology.

References

Ice rheology — PISM
Basal Shear Stress — tool.io

Similar or alternative tools

Thickness From Slope Driving Stress
Invert local shape-corrected slab driving stress for ice thickness; flat-slope inversions are undefined, and longitudinal stresses remain excluded.
Shape Factor Valley Correction
Estimate valley shape factor A/(P·H) from a flat-surface piecewise-linear bed section; not inversion from basal stress or a universal valley correction.