News from Greenland

[A colossal rockslide into Greenland’s Dickson Fjord scoured the surface of a glacier that fed the narrow channel, as shown in this image captured after the event. Wieter Boone. Science Advisor]

My eye was caught this morning by the piece in the FT at reference 1. A sort of seismic detective story which started about a year ago when seismologists around the world noticed a single-frequency hum, pulsing every 92 seconds, which lasted for nine days. On online academic message boards, the mysterious signal was ascribed to a USO, or unidentified seismic object. Now run down to '... a colossal landslide in a remote Greenland fjord that sparked tsunami waves up to 200 meters tall, the team reports today ... Like sloshing water in a bathtub, the tsunami resonated within the narrow valley, beating against the channel walls and creating the globetrotting seismic waves...'. The sort of thing we should expect as the glaciers of the world retreat - and for which there appears to be lots of precedent, both in the recent and in the remote past, in the margins of previous melting eras.

Lots of coverage of all this in the media, including the trailer at reference 2 and including BBC, but it all passed my by until today.

While the original paper in Science, reference 3, has to be paid for. A previous paper, reference 4, is in the public domain, as are pre-prints of the present paper. One from Oxford University and a rather better one from Aberdeen University - which is not double spaced and which omits the 'Confidential Pre-print' of the Oxford version stamped across every page. The start of it is snapped above. Just some of the vagaries of academic publishing. Of course, if you are a respectable person, affiliated to a respectable institution with a decent library, you will have access to the version in Science anyway and won't need to bother with a side copy.

Another taster. 'Fig. 5: Very long-period (VLP) seismic signal and comparison with simulated seiche. (A) … (C) Waveform recording from station II.BFO in Germany (29° away), showing dominant Rayleigh energy on the vertical and radial components, with weaker Love energy on the transverse. Indicative Q-values (black lines) highlight their slow, nonexponential decay. S-body waves arriving at 12:46 UTC (inset) carry the initial VLP signal. Synthetic seismogram envelopes (red lines) using the simulated seiche signal at the location of the landslide (Fig. 4E), scaled to a maximum horizontal force of 5 × 1011 N (29), match the maximum VLP amplitudes and their decay. All signals are 10- to 12 mHz bandpass filtered (D) ...'. All a bit too deep for me, but I am impressed by the detail with which one is able to model complicated events of this sort. And by the scientific cooperation across the world which makes it possible.

References

Reference 1: A seismic hum signals a new era of climate uncertainty: An enigmatic sound has shown that the frozen corners of the world are creaking — and in more ways than one - Anjana Ahuja, Financial Times - 2024.

Reference 2: A tsunami in a remote fjord rang Earth like a bell for 9 days: Scientists trace strange seismic signal to landslide that triggered sloshing, 200-meter-tall waves in Greenland - Maya Wei-Haas, Science Advisor - 2024

Reference 3: A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days - Kristian Svennevig and more than fifty others - 2024. Science.

Reference 4: Evidence of Middle Holocene landslide-generated tsunamis recorded in lake sediments from Saqqaq,West Greenland - Niels J. Korsgaard, Kristian Svennevig and four others - 2024.