A photo of Rialto Beach.

Sea stacks at Rialto Beach in Olympic National Park. The coastal landscape of the Olympic Peninsula reflects the interplay between two dominant forces shaping the landscape. One force is the ongoing crustal uplift associated with regional plate tectonics as the Juan de Fuca Plate is slowly being subducted beneath western North America. This process has cause the Olympic Peninsula to rise steadily over millions of years. The second force is coastal erosion which is influenced by the rise and fall of sea levels. During the last major ice advance of the Pleistocene Epoch, sea level was more than 300 feet lower than it is today. When the continental glaciers of the last ice age started melting about 15,000 years ago, sea level began to rise (again), and shorelines migrated landward, eroding material that was exposed by the gradual tectonic uplift of the peninsula. Wave erosion is constantly carving away at the shore, leaving behind more resistant rocks as sea stacks offshore (Harris and others, 1997; Tabor, 1987).