Landscapes from the Waves—Marine Terraces of California

Authors

Marjorie Schulz, U.S. Geological Survey
Corey Lawrence, U.S. Geological Survey
Daniel R. Muhs, U.S. Geological SurveyFollow
Carol Prentice, U.S. Geological Survey
Sam Flanagan, Bureau of Land Management

Document Type

Article

Date of this Version

3-2018

Citation

U.S. Department of the Interior / U.S. Geological Survey Fact Sheet 2018–3002 March 2018

Comments

U.S. government work

Abstract

M any coastlines around the world have stair-step landforms, known as marine terraces. Marine terraces make up a large part of coastal California’s landscape—from San Diego to Crescent City. Find out how these landscapes form, why marine terraces are of interest to scientists, and where you can explore these landscapes.

Marine terraces result from the interaction of two geologic processes: uplift of the land surface and the natural rise and fall of sea level over hundreds of thousands of years. As sea level rises, waves move underwater sediment—sand and gravel—back and forth against bedrock, acting like sandpaper to hone bedrock into flat, broad platforms.

When sea level falls, wave-cut surfaces are exposed above water. Earthquakes on California’s coastal faults, along with other processes that deform the Earth’s crust, cause uplift of the land surface. When uplift is fast enough, it causes wave-cut surfaces to be preserved as marine terraces above the influence of the ocean. Where land is not uplifted high enough, wave-cut surfaces will be flooded by the rising sea. It is important to note that high marine terraces seen along the coast do not represent past shorelines at that elevation, rather, they record ongoing uplift that occurs simultaneously with fluctuating sea level. The crust steadily moves upwards and high sea-level stands erode notches into the uplifting terrain.