William sent in this link to https://eos.org/articles/ancient-tsunami-tied-to-volcanic-flank-collapse… … which concerns the Italian island of Stromboli. It is in fact a volcano and has been periodically active since 1932 – but not on a grand scale. In the fairly recent past it has been more active – which seems to have caused the flanks of the volcano to collapse into the sea causing at least one major tsunami event to strike Naples. One of the ocassions was back in the 14th century AD – and the marine storm struck Naples in 1343. There was, it seems, three separate tsunami events (and collapses on the flanks of Stromboli) between the 14th and 16th centuries.
At https://phys.org/print469350189.html … is a story published in the journal Science (February 2019) of an earthquake in Bolivia in 1994 that was used as a data base to find mountains (or what seemed like mountains) and other topography in a layer 410 miles below the surface (separating the Upper from the Lower Mantle). To peer inside the Earth scientists used waves produced by the earthquake (seismic waves). Big earthquakes can shake the Earth. Shock waves produced by big earthquakes fan out in all directions and can travel from one side of the Earth to the other – and back again. What they found was the shock waves interacted with a barrier at the Lower/Upper mantle point, which seemed to suggest a feature as lumpy as mountains. Expect more on this in the future.