I haven't seen the details on this, but with that kind of mud, it's solid but it's supersaturated with water. Probably lots of fine clay and not much sand. You get some rain, and a little more water goes into the mud, and just a little more water, and all of a sudden it goes from solid to liquid in the blink of an eye--and then back to solid again as the water escapes, with the people caught inside.
In effect, it turns from mud with water in it to water with mud in it, then back again.
Ugh.
< After the 1995 slide, Varele said, he thought about the dangers "all the time."
"It was sort of our choice to live there. It's not that we're dumb. It's just that it's a wonderful place," he said.
No, I think you are dumb. At the very least, get out at the first sign of rain. It had been raining for days.
No way is this the gub'ment's fault.