Effective Pressure Nye

Calculate signed ice-overburden minus subglacial water pressure and flag pressure above overburden; negative effective pressure is not clamped or interpreted as stable contact.

Description

Effective pressure is ice overburden minus subglacial water pressure.

Effective pressure is ice overburden minus subglacial water pressure. Negative values indicate water pressure above the supplied overburden model.^[1]

Calculate signed ice-overburden minus subglacial water pressure and flag pressure above overburden; negative effective pressure is not clamped or interpreted as stable contact.

When to use Effective Pressure Nye

Use this for the following task: Calculate signed ice-overburden minus subglacial water pressure and flag pressure above overburden; negative effective pressure is not clamped or interpreted as stable contact.

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 Effective Pressure Nye 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 iceThicknessesM, waterPressuresPa, iceDensityKgPerM3, gravityMPerSecondSquared using the field table, then run the tool.
Read overburdenPressuresPa, effectivePressuresPa, aboveFlotationFlags. 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
iceThicknessesM	Ice thicknesses m	list of number; each entry: number	Required
waterPressuresPa	Water pressures pa	list of number; each entry: number	Required
iceDensityKgPerM3	Ice density kg per m3	number	Required
gravityMPerSecondSquared	Gravity m per second squared	number	Required

Pair nonnegative thicknesses and water pressures. Preserve signed effective pressure and emit 1 for aboveFlotationFlags only when effective pressure is strictly negative.^[2]

overburden = ρice g H; effective = overburden − waterPressure

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

Output field	Meaning	Value type
overburdenPressuresPa	Overburden pressures pa	list of number
effectivePressuresPa	Effective pressures pa	list of number
aboveFlotationFlags	Above flotation flags	list of number

json

{
  "input": {
    "iceThicknessesM": [
      100,
      100
    ],
    "waterPressuresPa": [
      800000,
      1000000
    ],
    "iceDensityKgPerM3": 900,
    "gravityMPerSecondSquared": 10
  },
  "output": {
    "overburdenPressuresPa": [
      900000,
      900000
    ],
    "effectivePressuresPa": [
      100000,
      -100000
    ],
    "aboveFlotationFlags": [
      0,
      1
    ]
  }
}

Limitations and assumptions

Negative pressure is not clamped or interpreted as stable basal contact. Some sliding laws require strictly positive effective pressure.

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 Weertman Basal Sliding Law for this operation: Evaluate a supplied Weertman-type power sliding law C·sign(tau)|tau|^p/N^q; coefficient is unit-specific and zero/negative effective pressures lie outside the model. For a complementary task, use Hydraulic Potential Shreve for this operation: Evaluate Shreve hydraulic potential p_w+rho_w·g·bed elevation with caller water/overburden ratio; potentials share a vertical datum and no geodesy transform is performed.

Further background: Subglacial hydrology.

References

Subglacial hydrology — PISM
Effective Pressure Nye — tool.io

Similar or alternative tools

Weertman Basal Sliding Law
Evaluate a supplied Weertman-type power sliding law C·sign(tau)|tau|^p/N^q; coefficient is unit-specific and zero/negative effective pressures lie outside the model.
Hydraulic Potential Shreve
Evaluate Shreve hydraulic potential p_w+rho_w·g·bed elevation with caller water/overburden ratio; potentials share a vertical datum and no geodesy transform is performed.