What about lava makes it so we can’t redirect the flow around neighborhoods with these things?
There’s footage of them saving the machinery being used to build the barriers.
Go to about 11:58 on the timestamp in the bottom right corner, you will see the lava flowing along the berm (which is doing a good job of protecting a large building) while workers with bulldozers and diggers close the gap in the berm that the road goes through.
The fissure close to the town opens up at about 12:20. The lava flowing behind the berm reaches the road at about 12:50.
See https://imgur.com/a/7WGO9M6 ; yellow are the defensive lines. Red are the fissures. Black is the lava; you can see how well it was redirected.
> Benedikt Halldórsson of the Met Office says houses are not designed to withstand lava flow.
> »... You can expect the walls to give way from the load, and the heat in the lava is such that it burns everything in its path.«
Apart from the heat, since it's molten rock it also has considerable mass, and the lava flow continues pushing from behind.
I had an opportunity to interact with lava during a Hawaii eruption, and people could run/walk across red hot and flowing lava, but it would start melting the bottom of your shoes. This lava was definitely on the colder end of the spectrum, with a consistency like bread dough.
On the the other end of the specturm, there are very hot low viscosity lavas similar in consistency to soup. If you tried to step on that, it would be like falling into a pool.