‘Beneath La Jolla’s Shores’: Oceanography talk in La Jolla will take a dive into underwater canyons and more

To spread awareness of local geographical features above and under water, the Walter Munk Foundation for the Oceans will present a free talk next week called “Beneath La Jolla’s Shores.”

The discussion, aimed at teenagers and adults, will begin at 4 p.m. Thursday, Dec. 1, at the La Jolla/Riford Library, 7555 Draper Ave. It will be led by Munk Foundation research director Greg Sinnett, who will explain the underwater geology of the La Jolla coast and the scientific legacy of Walter Munk, a famed oceanographer and La Jolla resident who died in February 2019.

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In what is becoming an annual celebration, the Walter Munk Foundation for the Oceans honored its namesake with an event at Kellogg Park in La Jolla Shores on Oct. 15.

A traveling model of the region’s topography (forms and features of land surfaces) and bathymetry (the shape of the bottom of the ocean) is housed in the La Jolla Library’s lobby. A permanent bronze version will be installed soon at The Map of the Grand Canyons of La Jolla, an educational plaza in Kellogg Park at La Jolla Shores that also is sponsored by the Munk Foundation.

Sinnett will use the model to punctuate his talk about La Jolla’s nearshore area, the surf zone to about 100 meters (328 feet) deep.

“I hope people will ask many questions about the model map and engage with [it],” he said. “That’s what it’s meant to do.”

Sinnett said the Munk Foundation hopes to take the traveling model to schools and museums to help people learn about the local topography and bathymetry.

Sinnett, a nearshore physical oceanographer who earned his Ph.D. at UC San Diego’s Scripps Institution of Oceanography — where he met Munk and his widow, foundation President Mary Coakley Munk — said he joined the foundation a few months ago to support its mission.

He said he will incorporate many aspects of geology and oceanography into his Dec. 1 talk.

Many who visit or live in La Jolla know about its sea caves, but not many know how the caves were formed, said Sinnett, who called it an “intricate story about the geology and the Rose Canyon faults and Mount Soledad and ancient rivers.”

The Rose Canyon fault, an active slip fault that runs north-south, helped create Mount Soledad by piling up the land at its bend through La Jolla, creating topography where water can flow and forming rivers that met the shoreline and carved the underwater canyons off La Jolla Shores, Sinnett said.

It’s all a “compelling geological story,” he said.

An illustration shows the La Jolla and Scripps underwater canyons off La Jolla Shores.

(Walter Munk Foundation for the Oceans)

The local underwater canyons — La Jolla Canyon and Scripps Canyon — affect how waves are focused, creating spots like Black’s Beach that are popular with surfers.

“As waves come in to shallower and shallower water … they slow down or maintain their speed, depending on the shape of the bottom,” Sinnett said. Black’s Beach has more focused wave energy due to its proximity to the underwater canyons, he said.

“All the major surf spots are the way they are because of the way the waves interact with the bottom,” Sinnett said.

Munk’s pioneering research described how waves focus or dissipate, Sinnett said. “And where they focus, you can expect big waves [and] lots of erosion,” he added.

Knowing where waves focus matters for onshore infrastructure, Sinnett said. He noted that Munk took what he learned about local bathymetry and waves and created a map of “how wave energy is expected to impact the coastline.”

Munk’s “groundbreaking oceanography” in La Jolla was applicable in other places and helped launch his career, Sinnett said.

Since 40 percent of the U.S. population lives in coastal counties, “you want to make sure that infrastructure is built in a way that can sustain [its] environment,” Sinnett said.

Bathymetric information is a component of current efforts to stabilize bluffs under seaside railroad tracks, he said.

Mapping of wave energy has remained consistent in the decades since Munk’s work began, Sinnett said, largely due to the slow change in bathymetry over time. ◆