Giant Underwater Volcano Discovered Off the Northern California Coast

A uniquely shaped underwater volcano, towering at 3,300 feet, has been discovered 184 miles off the Northern California coast near Cape Mendocino. The seamount exhibits a smooth-sided circular tower appearance with nearly vertical sides, differing from the typical sloped sides of seamounts.

The discovery was made in February by an ocean mapping autonomous sailboat during a multi-agency survey led by the National Oceanic and Atmospheric Administration (NOAA). Dr. Aurora Elmore, the program manager for NOAA’s Ocean Exploration Cooperative Institute, explained that the seamount’s unique shape could be attributed to the volcanic activity that formed it, which may have been “super hot, and happened all at once.” Alternatively, the structure might have lost a more gradually sloped base due to an accumulation of sediment called “marine snow.”

This seamount is also an anomaly because it is not located in the area of known seamounts off the California coast, expanding the range of these geological features. The 1,200-foot-deep crater at the summit of the newly discovered underwater volcano lies about 2 miles beneath the ocean’s surface. The discovery was made possible through the use of an uncrewed sailboat, Surveyor SD 1200, operated by Bay Area ocean research company Saildrone, in collaboration with NOAA and other agencies.

Setting sail from Alameda in July 2022, the Surveyor SD 1200 mapped Alaska’s Aleutian Islands before venturing down the California coast. The sailboat, equipped with a multi-beam sonar on its hull, maps the ocean floor contours remotely controlled by pilots at the company’s Alameda base.

The discovery has excited the oceanography community, as only 50% of the U.S. exclusive economic zone—an area within 200 miles of any U.S. coastline—has been mapped in this manner. Neah Baechler, lead surveyor for Saildrone, described the seamount as resembling a “Bundt cake,” round with steep sides and a curved top that slopes into a crater in the center. While similar features have been found on the ocean floor, rarely are they this large or complete.

Seamounts are the remnants of extinct volcanoes that formed millions of years ago on the ocean floor. They have a height of at least 3,300 feet from the seafloor to their summit. Occasionally, these underwater mountains breach the water’s surface, creating island formations like Hawaii. The newly discovered seamount off California’s coast is yet to be named, with the process soon to be undertaken by the General Bathymetric Chart of the Oceans’ Sub-Committee on Undersea Feature Names.

The team hopes to deploy a remotely-operated video camera to get a closer look at the underwater tower, which stands taller than Mount Tamalpais off the California coast. The study of these unique geological formations provides valuable insights into the Earth’s geological history, biodiversity, and deep-sea ecosystems.

Seamounts are known to host a wide variety of marine species, providing rich habitats for corals, sponges, and various types of fish. These ecosystems often serve as breeding grounds, migration routes, and feeding areas for marine life, contributing to the overall health and diversity of the oceans. Studying seamounts can also help researchers identify potential threats to these ecosystems, such as the impacts of deep-sea mining, climate change, and pollution.

As technology advances and enables more detailed exploration of the ocean floor, it is anticipated that more such discoveries will be made, further enriching our knowledge of the world’s oceans and their hidden wonders.