A ten letter word for something that occurs could be an occurrence or happenings.
You are looking for the word subaqueous.The definition of subaqueous is "something that us formed or adapted for underwater use" and "something that is found or occurs underwater".An example of a subaqueous object is a submarine.
A four letter word meaning the foundation of something is base.
occurance means "how often something happens or occurs"
have
Urge
The word you're looking for is "spontaneous." It means something that occurs naturally or without external influence.
An Acrostic
lose
Improve
Own
have
shard