Not very much. The lava mostly builds up, not out, and the sides of the islands are so steep that most of what reaches the sea does not increase the shoreline by much. If the volcanos that are active on the main islands were located on a shoreline – say Italy or the west coast of America, the flow onto the continental shelf would increase area, but not out there. References :
Check out this site.
References :
http://volcano.und.edu/vwdocs/HawaiiQuest/hawaii_quest.html
Not very much. The lava mostly builds up, not out, and the sides of the islands are so steep that most of what reaches the sea does not increase the shoreline by much. If the volcanos that are active on the main islands were located on a shoreline – say Italy or the west coast of America, the flow onto the continental shelf would increase area, but not out there.
References :