Map of seismic data across Greenland. Triangles mark 373 broadband and shortperiod stations. Colored triangles show on-ice stations with receiver function (RF) results, and color denotes number of RFs. Inset map shows teleseismic events (M >6, black dots) used in analysis. Ice thickness is from BedMachine version 5 (Morlighem et al., 2017, 2022). Histogram (right) shows ice-thickness uncertainties beneath each station from the same dataset. Credit: Geology (2025). DOI: 10.1130/g53653.1

In an age of rising sea levels, as polar ice sheets melt in a climate warmed by fossil fuel emissions, climate modelers are racing to understand what the future might hold for coastlines around the world. But uncertainties about how fast polar ice might melt make predicting coastal inundation difficult. Now, scientists think they’ve helped make one of those uncertainties, the material conditions underneath the Greenland ice sheet, smaller.

Seismic survey reveals sediment

In a study published in October in the journal Geology, researchers reported that a long-term seismic survey of the Greenland ice sheet revealed widespread soft sediment at its base. This means that the glaciers could be sending melting ice into the ocean and raising sea level even faster than previously thought.

"Greenland is a major contributor to global sea-level rise, but the ice loss projection suffers large uncertainties due to limited understanding in the basal environment," says Yan Yang, a geophysicist at the Scripps Institution of Oceanography at the University of California San Diego. "The safety of coastal communities depends on accurate forecasts, and knowing whether the bed is hard rock or soft sediment is essential for improving future sea-level change predictions."

Why sediment matters for glaciers

The composition of the bed, or ground beneath an ice sheet, makes a big difference for how fast melting glaciers add water to the oceans. Glaciers flow to their terminus by deforming internally, but they also slide over the ground. If that ground is made of hard bedrock, the glacier will flow more slowly. But, if the base of the ice consists of wet, loose sediment, the glacier speeds up and will contribute to sea level rise at a faster rate.

Other research had already confirmed the presence of sediment beneath some regions of the Greenland ice sheet, but difficult fieldwork conditions made a thorough accounting difficult. To get a more complete view, Yang and colleagues used publicly available passive seismic data, from sources like the Greenland Ice Sheet Monitoring Network and the XF network run by researchers at Columbia University’s Lamont-Doherty Earth Observatory. These networks involve placing seismometers on the ice to measure how the waves of energy generated by distant earthquakes move through Earth. Analyzing those waves lets scientists untangle what’s happening deep below their feet.

How seismic data reveals the subsurface

"To see what’s beneath the ice without drilling, we used seismic waves from distant earthquakes," says Yang. "As these waves travel through the ice sheet, like X-rays, they change slightly when they hit different materials, including ice, sediment, or bedrock. Greenland has many seismic stations that continuously record these waves."

By integrating these records from all over the ice sheet, Yang and the team were able to build the most complete picture yet of the basal conditions in Greenland. They found that sediments were far more widespread than they expected, occurring even under the thick ice far from the coast.

Implications for future sea-level rise

The distribution of sediment also appears to vary on a small scale, meaning that a denser network of seismometers is needed to make that picture higher resolution. Yang also wants to keep digging into the data to see how the distribution of basal sediments changes over time.

Even at the current resolution, though, these findings have direct and urgent implications for predictions of sea-level rise.

"Our results suggest that thick, weak sediments could make parts of Greenland more responsive to future warming. If more meltwater reaches the bed," says Yang, "these sediments may further reduce strength, speed up ice flow, and increase ice loss to the ocean. This means some regions of Greenland may be more vulnerable to climate change than current models assume."

More information: Yan Yang et al, Seismic evidence of widespread sediments beneath the Greenland Ice Sheet, Geology (2025). DOI: 10.1130/g53653.1

Citation: Widespread sediments beneath Greenland make its ice more vulnerable to warming (2025, December 11) retrieved 11 December 2025 from https://phys.org/news/2025-12-widespread-sediments-beneath-greenland-ice.html

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