BBC story here. These data indicate a smaller collapse, but also a shallower failure plane than expected, which allowed that smaller volume to still generate a devastating tsunami.
Basically, when modelling this, different combinations of slide volume and failure angle can produce the same size of tsunami: less rock spending more time moving through shallow water can generate as big a tsunami as more rock spending less time doing so. This is an example of what in geophysics we call the ‘inverse problem’: there are many possible ways of interpreting the incomplete (and often indirect) measurements of the thing we are trying to understand, all of which reasonably ‘fit’ the data we have.
We can use our geological knowledge of how the Earth generally behaves, or how we’ve seen specific systems like this behave in the past, to rule out some possibilities, but often – as in this case – the only way to further zero in on the real solution is more data.
The important point here is that smaller landslides tend to occur more often than big ones, which increases the potential tsunami hazard posed by collapses of Anak Krakatau and other volcanoes like it.
Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.