Caves and caverns are commonly confused with each other and the two words are often used interchangeably. It is indeed true that the two are very similar but there are certain differences that separate the two. We all know what caves are; and it is not very difficult to understand what caverns are because they are very similar in their appearance. It is just that at places where we need to be more specific, it is recommended to use the word that describes the actual thing more appropriately.
The dictionary meaning of a cave refers to a hollow that is in the earth. It usually has an opening into a hill or a mountain and that opening can be horizontal or vertical. Not all caves are naturally occurring; some such openings can be made by man also for various reasons. When we look at the word meaning of a cavern, we find out that it is also a type of cave but with some specific characteristics. A cave is a cavern if it is quite large and is underground. This means that if the hollow or the opening is on the surface of the earth then it is a cave whereas if it is under the ground then it is advisable to refer to it as a cavern.
The way that caves or caverns form is similar; they usually form naturally by the weathering of rock. They can also form as a result of volcanic activity, pressure, chemical actions, water erosion as well as the activity of microorganisms over long periods of time. Then there are sea caves as well that get filled with water sometimes, and are usually found along the ocean and sea coasts. These type of caves are formed due to tidal activity which erodes and weakens the rocks located there over a long period of time. Once formed, they can extend very deep underground. Note that when we say that caverns are usually larger caves, there must be some smaller caves as well. These include sea caves, grottos and rock shelters that, on average, usually have smaller openings.
A conclusion that we can derive from the information above is that whereas all caverns are also caves, the converse is not true.
Moving on, when we say cave, we usually mean just one cave or just one opening. However, the word cavern implies that there are a series or a system of caves or cave chambers. Furthermore, the open spaces of caves connected by various passages is what cavern refers to. The connections rise as a result of the weathering of rock.
Let us look at some more differences between caves and caverns. Caves are usually indug in what one might call a mass that is above sea level or above the ground as previously mentioned. Caves can be straight, upwards or downwards. Caverns, in contrast, tend to be extremely steep towards the ground instead of being upwards. In some cases, the cavers go so far that they break the water and that is what differentiates caves from caverns.
Most of the caves and almost all caverns are made up of soluble rock. Caverns can also create stalagmites. Also, it is caverns that have the ability to form speleothems.
Summary expressed in points
1) The dictionary meaning of a cave refers to a hollow that is in the earth, it usually has an opening into a hill or a mountain that can be horizontal or vertical, not all caves are naturally occurring; some such openings can be made by man also for various reasons; from the word meaning of a cavern: it is also a type of cave but with some specific characteristics, a cave is a cavern if it is quite large and is underground
2) Whereas all caverns are also caves, the converse is not true
3) Cave: just one cave or just one opening; however, the word cavern implies that there are a series or a system of caves or cave chambers
4) Caves can be straight, upward or downwards; caverns, in contrast, tend to be extremely steep towards the ground instead of being upwards
5) Most of the caves and almost all caverns are made up of soluble rock; Caverns can also create stalagmites and have the ability to form speleothems