How bad is this? 1/4 of the way into the long side of the house under the concrete perimeter.
Did it change or erode away due to the extra bad winter we had? I would have a foundation expert (or two) take a look at it, if anything, for peace of mind.
While you are at it, I may look into having the earthquake bracing or reinforcing done (if not already).
No, and we have pictures of this from when we purchased it 5 years ago, and I’d say that it’s actually very slowly filling up with mud rather than eroding away. Like maybe 1"-2" in 5 years.
It looks to me like either the sump pump pumped out a big hole or someone was trying to dig out that rusted pipe, but I just don’t know
On the top side - from the outside there are no cracks.
Put in a proper sump pit( they come in concrete or plastic.
Backfill around it with 3/4” crushed rock. Clean up th pump… make sure it runs properly
How bad is it to not fill it in at all? Is there a risk if a part of the concrete perimeter isn’t supported underneath?
Can’t say without a physical inspection. Obviously not a big problem if there’s no cracks or settling. The silt will clog the pump. The work I recommended will prevent that.