Morphological Gemination (MG) consists of the systematic 
gemination of a segment associated with a systematic 
change in meaning of the affected base. Any account of 
MG must deal with the following two issues:

(a) accurately model how the gemination occurs.
(b) predict where gemination occurs and which segment geminates.

As for (a), this analysis follows Lombardi and McCarthy (1990), 
recognizing the existence of a purely prosodic affix 
constituted of an empty mora. Gemination emerges 
when this affix is inserted in a base and filled by one 
of the nearby segments.

As for (b), the insertion site and the filling segment
follow from the interaction of the prosodic and syllabic 
wellformedness constraints of the language.  
It is therefore the tension between affix realization 
and prosodic well-formedness that determines 
what segment will geminate and where: the grammatical 
derivation being the one that least violates the prosodic 
and syllabic constraints while best realizing the affix.