I have seen in movies and studied some physics in which it is possible to have an underwater object filled with air and does not allow water in. Do caves exist underwater which exhibit this same effect (being totally submerged, but still dry on the inside)?
Underwater Caves With Air
Not likely. An underwater object that is filled with air and does not allow water in is contained in a nearly impermeable container, like steel. Rock, and especially limestones and dolomites which contain most caves are often highly permeable rocks. Air inside a cave subjected to hydrostatic pressure of water below it would quickly find its way through the microscopic pores in the rock around it to the surface. Where air pockets do exist in underwater caves the air pockets generally are above the water level found outside of the cave and are simply trapped by the water and rock, but not actually under the level of the water outside the cave. Changes in tide or dramatic changes in stream flow through the cave can open or close these trapped air pockets, but are more likely to cause them to flood than to submerge them without filling them. There are plenty of underwater caves, but not with air in them. Because sea level was once much lower than today, and because tectonic movement has lowered some parts of some continents below sea level, there are many caves that formed when sea level was below the cave and now are flooded and underwater.
