The Professor is, in my opinion, the site's authority on Old English, I'm sure he will end up popping up here soon to chime in.
You called?
@Hominid
You're referring to a couple of processes called breaking and a-restoration/retraction.
Breaking in the context of the Old English dialects is where stressed front vowels in a velar environment change to two by adding a schwa or similar:
i, e, æ to short and long diphthongs spelled
io, eo, ea when followed by
h or by
r, l + another consonant (short vowels only), and sometimes
w.
In the northern Anglian dialects, e.g. Northumbrian, Mercian,
ea (=
æa) was often retracted to
a. It's sometimes called a-restoration as the original
æ came from earlier a.
Most of our spelling and pronunciation is based on Mercian.