Science and CSU

Tsunami – 10 surges in 4 hours at Morro Bay




‘Had it been a few hours later…’

About 10 hours after the Honshu earthquake initiated a tsunami in Japan March 11, the first surges began to reach California’s coastline, including Morro Bay at 8 a.m.

Oceanographers at the San Luis Obispo Science and Ecosystem Alliance (SLOSEA) took heed and measurements. This report comes from its executive director, Dean Wendt, who is a biology professor at Cal Poly San Luis Obispo, which coordinates SLOSEA from its Center for Coastal Marine Sciences.

It refers to the graph above, which shows a day’s worth of normal changes in tidal height, followed by 10 tsunami-generated surges over the next four hours. Note how the second surge was the biggest, causing the water level to rise about 7.5 feet in about 15 minutes. (Click graph to enlarge it.)

From Dean Wendt of SLOSEA:

“In light of today’s news regarding the 8.9 magnitude earthquake that struck off the coast of Japan, and the resulting tsunami, we at SLOSEA wanted to share with you the impacts felt here in Morro Bay.

 “…The SLOSEA water quality monitoring network captured the arrival of the Honshu Tsunami when it hit our local community at 8 a.m. (see graph). We are fortunate that its arrival coincided with low tide. Had it arrived even a few hours later, we would have seen a much larger impact to our coastal towns and communities.

“As you can see from the graph, we saw swings of almost 8 feet in tidal height within very short periods of time (about 15 minutes). This volume of water movement would normally be seen under our most extreme tides and over a six-hour period.

“In just a few hours the bay ecosystem underwent as many high and low tides as it does normally during five or more days. Observing this movement of water firsthand was both exciting and frightening.

“These data are available thanks to our research team, led by Dr. Mark Moline with Research Associate Brian Zeleke and SLOSEA Fellow Johanna Weston.

“We send our thoughts and prayers to the people of Japan and other coastal communities around the Pacific during this period of incredible tragedy and loss.”

For real-time water-quality data, visit SLOSEA’s site at .For more about this and our other SLOSEA research initiatives, send email to