Jökulhlaups!

glacial geomorph not my field so Im talking outta my ass here.
Glacial damm breaks are pretty well documented from past events in Canadian and US geological survey reports. We call em "Glacier Bursts" (I had to look up your Icelandic term in my Int Geo Dictionary).
The catastrophic kind that would be vulcanism caused are pretty much able to describe "Glacial melt benches" or scabland deposits on maps. (Id use some LIDAR and look to use "Slope SHade models".
So Id maybe want to look at some old glacial bursts and compre where the discharges wound up nd what ptterns they described.
We always use past events to help us model future ones.
Thats all I can come up with Im sure theres other geologists on the line with more experience in this area.

If its in a glacial recessional channel, I think itd be a piece of cake. However, if its a melt burst that covers an area like the Delmarva Peninsula, youll have to look at the gravel nd sand deposits.

Why not just do a graphic model and use other past bursts to calibrate it. Thats what they do to predict meteor craters .