An unsealed hole underground would have to be dug to the same depths as that crater. If you're pressurizing it, you'll probably target 1 bar to live in it, inst

An unsealed hole underground would have to be dug to the same depths as that crater. If you're pressurizing it, you'll probably target 1 bar to live in it, instead of 600 KPa. A glacier that has the pressure to melt ice, would have more than enough pressure to keep it from sublimating. A rough estimate says that a foot or so of ice could provide over 600KPa of pressure, but that doesn't account for any means of keeping the water liquid or the ice solid. However, I wouldn't expect to actually find that on Mars. You might be able to keep water that way for a while until it froze again.