If you are plugged in today, you've likely seen the report about a paper in this week's Nature about a ice dam-bursting megaflood scouring event that is thought to have produced the English Channel. I simply don't have the time at the moment to comment on this in any detail....so here's a few blurbs from a New Scientist report.
Half a million years ago, Britain was connected to mainland Europe by a broad chalk ridge that spanned what we now call the Dover Strait (or the Pas de Calais in French). But somehow that ridge was destroyed, forever separating England and France.
The cause was revealed by an ultrahigh-resolution sonar survey of a large chunk of the channel's bedrock. It shows the Weald-Artois Ridge, as it is called, was breached and toppled by a monumental torrent that gushed from an overfilling glacial lake that the ridge had been damming on its northern side.
Not so long ago, I posted about the Channeled Scablands of the northwestern United States.
The Imperial team calculates that 1 million cubic metres of water per second flowed for several months to carve the seafloor valleys, some of which are up to 10 kilometres wide and 50 metres deep. The flow rate was 100 times the average of the Mississippi river today, and 1000 times that of the Rhine, Gupta says.
It turns out a study in 1985 hypothesized these features and inferred processes from some much lower resolution sonar data. Must be kind of cool to see your theory confirmed with higher resolution data like that.The BBC has a good summary of the Nature paper too.