For those who love spelunking, finding caves is often a matter of discovering the openings on the surface and then working your way lower into the ground. Many caves might start out with just a small opening that is really no larger than a house or even a doorway, but there could be miles of tunnels under the ground. The caverns could be huge, with soaring ceilings that are even larger than any room you have ever stood in before. It is very fun to explore all of these areas as long as you have the right equipment so that you can stay safe.
Have you ever considered the fact that there could be more caves that are simply hidden under the ground, that do not have an entrances that people can see? These caves could be larger than the ones that you have been in before, but you would never know they were there. You could walk over the top of them without knowing what lay just twenty feet below the soles of your shoes. This is something that people are often investigating with geophysical instruments manufacturered by Advanced Geosciences, Inc. They are looking for new caverns and caves that have never been explored before.
The instruments do this by looking at the resistance in the ground to electricity. When the ground is made from one solid material, the resistance levels are going to look the same, no matter how far down the impulses go. If there are different materials, the resistance could increase or decrease accordingly; as you can imagine, the electricity will move through solid rock much more slowly than it would move through something like sand. By looking at how fast the current can travel, you can effectively see what is beneath the machine to a certain depth, mapping it all out.
The way that this could be used to find new caves is that you would simply look for large patches where the resistance dropped to nothing at all. That would indicate that the electrical current was traveling through the air. It also might not be able to travel through the air at all if it is too weak, and so the current will stop and the signal will be lost. The cave may still not be accessible, depending on how deep it is, but you can at least know where to look for new explorations.