A seiche is a standing oscillation of water in an enclosed or partly enclosed basin. After landslide-generated tsunamis in Greenland's Dickson Fjord in September and October 2023, Monahan and colleagues used Surface Water and Ocean Topography (SWOT) satellite measurements to map cross-fjord differences in water-surface height. The slopes were consistent with a standing wave across the fjord. To interpret these sparse snapshots, the researchers related them to the phase of very-long-period seismic recordings and examined tidal and wind-driven alternatives. Together, these analyses supported the post-tsunami seiche explanation.

SWOT did not continuously record the oscillation: the September seismic signal lasted nine days, but the satellite provided only occasional passes. A tilted water surface in one pass alone therefore does not establish a seiche or the total seiche amplitude from SWOT snapshots alone.

Some satellite passes were affected by noise or artifacts, and relating the satellite observations to seismic phase depends on uncertain propagation estimates.

Monahan et al. (2025), Observations of the seiche that shook the world.