F Russell writes:

On Sun, 12 Jul 2020 06:19:20 +1000, Rod Speed wrote:


Depends on why it has subsided like that.


The house was built on this suburban lot about 60 years
ago.

That wouldn't make any difference.

The subsidence has been very slow. In fact it is a not an
uncommon occurrence. Concrete driveways sometimes subside
and there are companies that offer a "pump it up" solution
as a cheaper alternative to replacement.

I'm not concerned about sinkholes. I just want to know
if exposing 12-18" of the top basement wall poses any
problem.

Slow is a good sign, I'd still want to understand why that dirt left.
A 12-18 inch hole near the house should be collecting water,
that's NOT good. Fill it in. If there is a surface water issue,
dig a trench, add gravel, a perforated pipe, etc. Check YouTube
for fixing drainage issues.


--
Dan Espen