Collapsing stone when there is no stone?

Question

I've recently undertaken some surface mining in DF, and I've having more collapses (and dead dwarves) than I ever did underground.

I have a ridge like

    ------
    xxxxxx
---------------
xxxxxxxxxxxxxxx

which I designate for digging like so

    ------
    dddddd
---------------
xxxxxxxxxxxxxxx

Somehow I'm still getting a huge collapse which is killing my miners. Is the "layer" dropping on my dwarves?

---

Legend:

• x: stone of some sort
• -: the layer
• d: designated for digging
• : open space

Answer 1

Short answer: Yes. Soil is just as deadly as stone when it comes to cave ins.

Rather than dig the ridge out from under it, go up one z-level and tell your dwarves to channel instead. They'll clear the same area, but as channeling also removes the soil floor tiles, it won't result in any cave-ins. (Though you may need to clear some trees, biome depending)

A safer alternative is to turn the hill into Upward Ramps (with R or r, I think?) and then remove the ramps with z. A two-step process, but no cave-ins, and no falling dwarves (even 1 z-level falls occasionally cause injuries).