Dome Rock, a
Photo date 6/04, © S. Veatch.
Pikes Peak Granite, a plutonic rock (a rock formed at depth by crystallization of magma), was formed deep in the earth under high pressure. When the once deeply buried Pikes Peak Granite was exposed at the surface by uplift and erosion, pressure was released. Because Pikes Peak Granite is slightly elastic—just like all rocks—it expands from the release of pressure from the once overlying rocks. The expansion forms pressure release fractures (cracks) parallel to the surface of the granite and the outer layers peel off or “exfoliate”. The result is an exfoliation dome.
Water is also a part of the physical and chemical weathering at work forming Dome Rock. During the winter when water enters the cracks and freezes, the ice expands, widens the cracks, and loosens the sheets. Rainwater and groundwater contains dissolved carbon dioxide forming carbonic acid. This weak acid decomposes feldspar and ferromagnesian minerals in the granite, which also weakens the granite. The weathering of these minerals (into clay) give Pikes Peak Granite its pinkish color; other granites are much grayer.
These processes of physical and chemical weathering cause slabs of granite to break off along the pressure release fractures, forming exfoliation domes. The slabs of rock that fall off are termed exfoliation sheets. Other exfoliation domes can be seen throughout the Pikes Peak region and in other parts of the nation. Perhaps the most famous exfoliation domes in the United States are Stone Mountain, Georgia and Enchanted Rock in the Hill Country of Texas.