Taking a deep dive into the Unique Bathymetry of California’s Coast

Author

Theodore Gryn

American River College | Geography 350 | Fall 2023

Abstract

The purpose of this project was to explore the different types of bathymetric data sets and products that are available to the public from the government and private institutions that physically collect this type of data.

Introduction

The beauty of the Pacific Coast and its otherworldly underwater landscape has long been a source of fascination and wonder. The unique seafloor topography, combined with the upwelling of nutrient rich water, supports a diverse ecosystem of kelp forests, and the many different species of sea life that call the rocky coves, and sandy beaches, home. The study of the ocean floor provides us with a unique opportunity to peer into a world that is otherwise unseen by human eyes, and it is though this sort of exploration that we can gain insight into the geologic processes that form the physical world around us, and the rich ecosystems that support many communities around the planet.

Background

According to NOAA, bathymetry can be defined as the study of the "beds" or "floors" of water bodies, including the ocean, rivers, streams, and lakes. This is often facilitated by the collection of data using specialized equipment that utilizes Sonar, Lidar, and other remote sensing technologies. These efforts conducted by government agencies and privately funded research institutions have provided us with a wealth of information regarding what lies below the ocean’s surface, yet only 10 percent of the Planet’s seafloors are mapped today. Much of the data that has been collected over the decades is publicly available through online resources such as NOAA’s National Centers for Environmental Information Bathymetric Data Viewer.

Methods

The bathymetry data sets were acquired from NOAA’s National Centers for Environmental Information Bathymetric Data Viewer and consist of two Multibeam Bathymetry Mosaic’s and one Coastal Lidar dataset. The datasets were selected for three unique locations along California’s coast.

Figure 1. Project Locations

Results

The first data set is a Multibeam Bathymetry Mosaic for an area that is adjacent to the California/Oregon border. The Gorda Ridges are an oceanic spreading center which is the result of the unique plate dynamics that are occurring at this location. The are experiences frequent seismic unrest and has several areas of submarine volcanic activity.

Figure 2. Gorda Ridges and surrounding area

Several submarine canyons were evident to the east of the ridges. A few of the submarine canyons were obviously related to rivers of today, such as the Eel River and Eel Submarine Canyon. Yet, several submarine canyons were missing a modern associated river, a reminder that rivers are meandering bodies.

Figure 3. Submarine canyons south of Eureka, CA

Another feature that stood out from the data were a number of seamounts, rising from the sea floor and scattered throughout the area.

Figure 4. Seamount and depth in meters

The next location was the Monterey Canyon located on the outskirts of Monterey Bay. The submarine canyon is the largest on the West Coast, its main channel is over 292 miles long and it is 12 miles wide at its widest point. The exact origin of the canyon is still debated but several theories have been offered. The canyon, combined with currents of the Pacific Ocean are the main drivers in the upwelling of nutrient rich seawater that supports the diverse ecosystem that is present in Monterey Bay. The data set is a Coastal Lidar Mosaic and represents only a small portion of the canyon due to limitations with Lidar technology and the waters depths.

Figure 5. Monterey Canyon Coastal Lidar

The final location was Cortes Bank, a shallow seamount located approximately 110 miles from San Diego, CA in an area that is notoriously dangerous for maritime navigation due to numerous shallow shoals and the occurrence of rogue waves. The site is also home of the “Ghost Wave” which is a large open water breaking wave that can approach 80 to 100 feet in height and is surfed by a select few elite big wave surfers.

Figure 6. Cortes Bank Multibeam Bathymetry Mosaic

Analysis

Overall, the data sets were extremely easy to work with and interpret. The mosaic data sets can be easily downloaded from the Bathymetric Data Viewer and opened with ArcGIS Pro. I made slight adjustments to the shaded relief and selected appropriate color schemes to display the data sets in a way that the unique terrain features of the seafloor are easily distinguishable.

Conclusion

In conclusion, the bathymetric data sets that are available for free to the public are insightful and fun to look at. They represent a form of exploration that can be undertaken from the safety and comfort of your home because a bunch of fairly adventurous and intelligent scientists have dedicated the time and effort to head out to sea and collect this type of data. But much of the work remains to be done. Today, only 10 percent of the world’s seafloors have been mapped, as humanity continues to advance technologically, the opportunity to finally uncover what awaits below may finally become a reality.

Resources

Meldahl, Keith. Southern California’s Biggest Waves— The Story of Cortes Bank.

“Cortes Bank: The Phantom Wave of the Pacific Ocean.” Surfer Today, 7 May 2022, https://www.surfertoday.com/surfing/the-mechanics-and-history-of-cortes-bank.

NOAA. “What Is Bathymetry .” NOAA, https://oceanservice.noaa.gov/facts/bathymetry.html.

UK Hydrographic Office. “A Guide to Bathymetry .” UK Hydrographic Office, 2020.

California Gorda Ridge Photo Album. https://plate-tectonic.narod.ru/californiamargingordaridgephotoalbum.html.

Clague, David, et al. “MBARI’s 2000 Expedition to the Gorda Ridge.” Ridge Events, Oct. 2001

“Monterey Canyon: A Grand Canyon beneath the Waves.” Monterey Bay Aquarium Research Institute , 18 Aug. 2020, https://www.youtube.com/watch?v=xDbKaQOrgPo.