Here's why:

* Weathering: This is the process of breaking down rocks, soil, and minerals through contact with the Earth's atmosphere, biota, and water. In the case of caves, chemical weathering is the most important factor. This involves the dissolution of rock, often limestone, by acidic water.

* Example: Rainwater absorbs carbon dioxide from the atmosphere, becoming slightly acidic. This acidic water seeps through cracks in limestone rock, dissolving it over time, creating caverns.

* Erosion: This is the process of moving weathered material from one place to another, typically by wind, water, or ice. While erosion is important in shaping the interior of a cave, it is secondary to the initial process of weathering that creates the cave space.

In short, weathering breaks down the rock to form the cave, and erosion further shapes and modifies the cave's internal features.