Cave Shields

The Parachute Formation is one of the most highly photographed cave shields in Lehman Caves

NPS PHOTO

Cave Shields: The Wonder of Lehman Caves

Throughout Lehman Caves, visitors may easily spot these large round speleothems. These are called cave shields, and it’s estimated that Lehman Caves contains over 500 of them. Although cave shield formation is still puzzling, it is hypothesized that cave shields form as extensions of joints or cracks in the floor, wall, and ceiling. The process begins when calcite-rich water under hydrostatic pressure moves through the joints within the bedrock. Once the water exits the joint, it loses carbon dioxide to the cave chamber and precipitates calcite on either side of the joint. This builds plates of concentrically layered calcite separated by a thin, capillary-sized crack called the medial crack. Shields grow bigger as more calcite is deposited on the outer rims of the plates. As you can imagine, the larger the shield, the longer it took to grow.