# Estimating effective pressures in active subglacial lakes with ICESat-2 satellite altimetry

## TL;DR

This study uses satellite data to estimate pressures at the base of glaciers, revealing insights into how water affects ice movement.

## Contribution

A new method is developed to estimate effective pressures in subglacial lakes using ICESat-2 altimetry data.

## Key findings

- Effective pressure deviations are typically small, often less than 10 kPa.
- Large effective pressures, exceeding 100 kPa, were observed in some subglacial lakes.
- The method provides new data to improve subglacial hydrology models.

## Abstract

The difference between the ice and water pressures, or the effective pressure, influences water flow and sliding at the ice-bed interface. Effective pressure is typically quantified with subglacial hydrology models because direct measurements of the subglacial environment are sparse. Active subglacial lakes provide an opportunity to constrain effective pressures with altimetry because subglacial water-volume changes manifest at the ice-sheet surface as elevation-change anomalies. Here, we develop a method for estimating effective pressures from altimetry data above active subglacial lakes. We synthesise a previous theory of subglacial lake effective pressure with an altimetry-based inverse method that relates elevation-change data to water-volume changes. We apply the method to elevation-change data from NASA’s ICESat-2 satellite altimetry mission over several active lakes in Antarctica. We find that deviations from flotation (zero effective pressure) are typically a negligible fraction of the overburden (e.g., 10 kPa), although larger deviations can arise when the ice viscosity is large. For example, effective pressures over subglacial lake Byrds10 in East Antarctica locally reached magnitudes on the order of the tensile strength of glacier ice (e.g., over 100 kPa). These effective pressure estimates can constrain subglacial hydrology models in regions with active subglacial lakes and provide new insights into glacier-bed dynamics.