California Geological Survey Scientists Assess Coastal Damage After Volcanic Tsunami Across the Pacific

An underwater volcanic eruption in Tonga sent a small but damaging series of tsunami surges toward the California coast in January.

The incident prompted both an immediate response from California Geological Survey (CGS) scientists and a longer-term discussion about how to better protect lives and property on the state’s coast.

CGS produces maps and other products that help coastal communities, harbormasters, and the maritime industry plan for tsunami hazards.

Tsunamis are not as frequent as earthquakes and landslides. But they have left their mark on the state. In 2011, a huge earthquake in Japan generated a tsunami that caused roughly $100 million in damage to California.

Volcanic Eruptions Causing Tsunamis?

The Tonga event didn’t cause nearly as much damage – an estimated $10 million – but it was the cause of the event that caught scientists’ attention. The CGS maps that influence evacuation planning and harbor buttressing consider tsunamis caused by large distant quakes or landslides or, on the far north coast, local offshore quakes.

As far as scientists know, the Tonga event was just the eighth time a volcanic eruption caused a tsunami surge to cross the ocean.

Volcanic eruptions are now a possibility that may have to be accounted for in future maps.

CGS scientists were dispatched to several California ports and harbors, where the tsunami surges arrived at high tide.

One scientist saw small but strong surges roll into the Berkeley Marina, forcing a couple of boats to abandon their efforts to enter the harbor.

Another saw fishermen chased off the beach at Morro Bay as the tsunami dragged some of their gear out to sea.

The Hardest Hit: Santa Cruz and Ventura

There was flooding in Santa Cruz. Saltwater damaged the sea wall, some harbor infrastructure, and electrical transformers, knocking out power at a marina where many people make their homes.

Less severe than Santa Cruz, the damage in Ventura was dramatic.

Among other things, a harbor patrol boat was swamped by the current, bumped a sister craft, then capsized – watch the video here.

In the words of Rick Wilson, who heads the CGS Tsunami Unit: “It’s amazing how much damage even a small tsunami can do.”

Watch a short video of CGS’ post-tsunami response and field team observations from the Tonga tsunami, hosted by engineering geologist Nick Graehl.

Follow CGS on Twitter @CaGeoSurvey for up-to-date geologic information and conversations with CGS scientists.

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