This was interesting and may well have impact for cruise ships in the general vicinity of the activity.

http://www.cnn.com/2015/07/25/americas/kick-em-jenny-volcano-rumbling/index.html

"To clear its path and reduce risks, scientists set up an exclusion zone for ships around the volcano. Recreational ships must stay at least 5 kilometers (3 miles) away from the summit of the volcano. Underwater or submarine volcanoes release intense amounts of gas into the sea during eruptions -- and at times in between eruptions during a process called degassing. Such gas bubbles lower water density and can cause ships to lose buoyancy and sink."

I'm not sure about anyone else but buoyancy is a top-of-the-list issue for me when it comes to cruising.  What do you think?