This would be called a cave.
Hole
a core
A hollow or depression in the earth's surface is a basin. A basin is usually shaped like a bowl, with the sides higher than the bottom. Some are filled with water, some are empty.
A geode forms in a pocket or hollow circular shaped opening in sedimentary or igneous rock. The opening could be created by a gas bubble, a rotted organism, or by other means. Mineral filled solutions seep into the opening and gradually form crystals from the hole lining inward. If the hole completely infills, it becomes a nodule. Because the minerals that form inside the pockets are often silicate, they are resistant to weathering. This means that the rock surrounding the pocket may not be as resistant to weathering as the geode pocket. Once the surrounding rock has weathered and eroded, what remains on the surface is the geode or nodule. Once an empty circular shaped hole it is now a rock formation unto itself.
Temperature and pressure is the answer. Also, a piece of ice will melt faster when there is more surface area like with a hollow ice cube.
Hollow spheres in a limestone rock could be called pockets or geodes.
Liar A place inhabited by a wild animal, often a cave or a hole in the ground. Cave A hollow or natural passage under or into the earth, especially one with an opening to the surface.
a cavity,opening,or space within somethingwhen something is hollow t has nothing inside it (when a tree is hollow it is empty)
a cavity,opening,or space within somethingwhen something is hollow t has nothing inside it (when a tree is hollow it is empty)
Clover Hollow Natural Area Preserve was created in 2005.
The area of Clover Hollow Natural Area Preserve is 101,171.41056 square meters.
The area of Hickory Hollow Natural Area Preserve is 1,027,901.5312896001 square meters.
a valley
The volume of a square hollow bar is calculated by multiplying the length of the bar times the width of the opening times the height of the opening ( inner dimensions ).
cavity, hollow, mouth, opening
The area of Stillhouse Hollow Falls State Natural Area is 364,217.078016 square meters.
a cavity,opening,or space within somethingwhen something is hollow t has nothing inside it (when a tree is hollow it is empty)
A hollow tree is the natural home of a honey bee.