Hi Alan,
Eysteinn sent me some more details about 'í gegnum' in Modern Icelandic:
> "í gegnum" simply means "through", while "in through" would have to
be "inn í gegnum". But normally we often use simply "inn um" where you
would use "in through". For example, we would say "hún kom inn um
baðherbergisgluggann".
> If we said "hún kom inn í gegnum gluggann", it would sort of mean
that she smashed through the glass and all.
I think I see what you mean about 'at hausti': like we might have a
choice between "in the autumn" and "during/over the autumn", all of
which could refer to the same extended activity and mean basically the
same thing, but 'during' and 'over' emphasis extended time more,
whereas 'in' doesn't pay any particular attention to duration or
otherwise? I don't know enough to say if Icelandic makes the same
contrast with 'at' ('að') and other prepositions. Looking at Google
just now, I got 50 500 hits for 'að hausti', 741 'á hausti', 106 í
'hausti', and just 39 for 'um hausti'. I wonder what factors
(meaning, context, convention, etc.) influence people's choice of one
or the other of these, and whether this usage has changed over time.
Oh well, it'll soon be winter anyway...
LN